Basic Principles of Cleaning and Disinfection in Food Manufacturing

DOC

BASIC

European Hygienic Engineering and Design Group

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BASIC PRINCIPLES OF CLEANING AND DISINFECTION OF FOOD MANUFACTURING EQUIPMENT*

July 2021 ©EHEDG

Cecilia Svensson Tetra Pak Processing Systems AB, Sweden

Thierry Bénézech INRA URGPTA, France

Hansruedi Mürner Halag Chemie AG, Switzerland

Thomas Johnson QleanTech Enterprises, LLC, USA

Thomas Tyborski Ecolab Deutschland GmbH, Germany

Hein Timmerman Diversey, Belgium

Frank Moerman

John Holah

Sebastien Fastrez

Katie Satterthwaite

Patrick Wouters

David Childs

Dirk Nikoleiski**

Corresponding team member:

Alexandra Velasquez

Catholic University of Leuven – KU Leuven, Belgium Kersia, UK

REALCO S.A., Belgium

Marks & Spencer, UK Cargill, NL Kersia, UK

Commercial Food Sanitation (an Intralox Company), Germany ERIES UV Systems, France

* Report prepared by the Working Group "Cleaning and Disinfection" of the European Hygienic Engineering & Design Group (EHEDG)

** Chairman

Summary

This guideline aims to provide a basic understanding of the cleaning and disinfection of food manufacturing equipment and their environment. It is intended to help stakeholders within a food manufacturing facility to make the correct choices when developing cleaning programs by offering guidance on soil characteristics, wet and dry-cleaning methods, as well as disinfection methods.

The guideline can also help designers and manufacturers of hygienic entities to understand the needs of endusers when specifying and building these entities.

Introduction

Hygienic design principles are applied to allow for effective and efficient cleaning, disinfection and sterilisation regimes inclusively, and to minimise cross-contamination risks. In turn, the application of validated cleaning and disinfection regimes belong to the prerequisite programs (PRP) required in a robust HACCP system - hazard analysis and risk assessment, based on ISO 22000 [21] - for a food manufacturing facility.

The intent of cleaning is to remove contaminants from food and beverage contact and splash zone surfaces. Contaminants take many forms, physical, chemical and microbiological. They include for example soils, lubricants, grease, blood, chemical and food residues, food allergens, and microorganisms. Once a surface has been successfully cleaned, then a disinfection step may be required. The difference between a disinfected surface and one that is sterile, is a matter of numbers. A sterile surface is one that is completely free of viable microorganisms, whereas on a disinfected surface viable microorganism may remain at a predetermined acceptable level.

Cleaning and disinfection processes are carried out to leave surfaces in a hygienic condition that is indispensable for a clean production process ensuring food safety while adding value and allowing product and resource conservation.

Objective and Scope

This guideline is intended for stakeholders within the food industry to provide a basic understanding of the principles, methods, and elements of cleaning and disinfection regimes which can be applied to food manufacturing, processing, and serving equipment, as well as the manufacturing areas these entities are placed in. It shall help to make the correct decisions about cleaning and disinfections strategies when it comes to the design and fabrication of hygienic entities, as well as implementing and improving cleaning and disinfection programs for existing installations.

Out of scope is sterilisation, and any treatment of packaging materials used to pack food.

Normative References

For the purposes of this Guideline, the latest approved version of the following referenced Guidelines and other documents shall apply, unless otherwise noted.

EHEDG Guideline Doc. 8, Hygienic Design Principles

EHEDG Guideline Doc. 28, Safe and Hygienic Treatment, Storage and Distribution of Water in Food and Beverage Factories

EHEDG Guideline Doc 45, Cleaning Validation, Monitoring and Verification

EHEDG Guideline Doc 50, Hygienic Design requirements for CIP Installations

Local food laws and regulations that require cleaning and disinfection (if deemed necessary) should be referred to as appropriate. Relevant international (ISO), European (EN) and national standards and guidelines are included in chapter 11. At the time this document was prepared, the editions listed were valid. All documents are subject to revision, and parties are encouraged to review the most recent editions of the documents indicated.

Definition of Terms

The current approved version of the EHEDG Glossary shall apply.

Complex Forming Agents

Also referred to as chelating agents or sequestrants They will keep dissolved metal ions in solution and prevent chemical precipitation. Typical complex forming agents are phosphates, EDTA (Ethylenediaminetetraacetic acid), or citrates.

Detergent

A surfactant-based formulation used for cleaning which contains water-soluble active substances. In the industry, the term is often wrongly used to describe any solution used for cleaning.

Open-Plant-Cleaning, OPC Cleaning (automated or manual) of exposed surfaces, which may or may not include dismantling to improve accessibility.

Oxidisers

Also referred to as oxidising agents that induce an oxidation reaction by gaining electrons from other atoms or ions. Due to this reaction, the oxidising agent is converted to another substance. Typical oxidisers used for cleaning and disinfection are peroxides, peracids, or hypochlorite.

Pressure washing (low, medium, high)

Pressure washes are used to wash down equipment or an area with the intention to remove surface deposits. Depending on the pressure applied systems are divided into low, medium, and high-pressure washers.

• Low pressure: 3x105 -10x105 Pa

• Medium pressure: 10 x105 -40x105 Pa

• High pressure: > 40 x105 Pa

Sequestrants

See Complex Forming Agents.

Surfactant

Short form of ‘surface active agent’. The hydrophobic end of a surfactant molecule is attracted to fat/oil and the hydrophilic end to water. Dissolved in water a surfactant surrounds hydrophobic soil and forms aggregates with the hydrophobic end getting away from the water and the hydrophilic end staying next to the water (‘micelles’). Most surfactants can be used as wetting agents.

Surfactants are classified as anionic (traditional soaps), cationic, non-ionic and amphoteric, depending on their ionic charge in solution. Their properties will depend upon the ratio of hydrophilic/hydrophobic portions, pH, and the temperature conditions.

Visually Clean

Visible cleanliness confirmed by visual inspection conducted by a trained inspector. Acceptance criteria is the absence of any visible residue after cleaning.

Wetting Agents

Substances that reduce the surface tension of water. Reduced surface tension weakens the cohesive properties of water and thus the penetration of a solution into the soil is improved.

General Considerations

The current version of the EHEDG Document 8, Hygienic Design Principles and Doc. 34, Integrating Hygienic Entities” shall apply, unless otherwise noted herein with additions, clarifications, exceptions, modifications, or exclusions,

Along with Good Manufacturing Practices (GMP) and relevant prerequisite programs (PRP), cleaning and disinfection forms parts of every HACCP based food safety system. It generally begins with an effective cleaning procedure (dry and/or wet) which may be immediately followed by an effective disinfection procedure to produce hygienically clean surfaces.

A cleaning process can be considered to consist of the removal of organic and/or inorganic soil from the surface, the dispersion of the soil into the cleaning medium (wet cleaning) and the prevention of soil re-deposition back on to the surface.

Disinfection is the reduction, by means of chemical agents and/or physical methods, of the number of microorganisms to a level that does not compromise food safety or suitability (see also EHEDG glossary).

Cleaning and disinfection are carried out for multiple reasons (list not exhaustive):

• To minimise food safety risks such as allergens, pathogenic microorganisms, chemicals (e.g., lubricants) and physical hazards (e.g., glass, stones etc.).

• To minimise food spoilage risks

• To protect brand integrity such as preventing transfer of one meat species (e.g., pork) to another meat product (e.g., beef), or inclusion of animal proteins in a product labelled as ‘suitable for vegetarians’.

• To avoid flavour carry-overs.

• To control genetically modified organisms (GMO), which may be a requirement.

• To comply with legal requirements and specific customer requirements or standards (e.g., GFSI recognised standards such as BRC, IFS), Codex Alimentarius, and for products which may be exported to the U.S., compliance with the Food Safety Modernisation Act (FSMA) with enforcement of all of its criteria which came into effect January 1st, 2017, and the FDA Food Code.

• To maximise productivity of each process run, i.e., whether cleaning and disinfection breaks are required during production runs (e.g., every 4 hours), or when cleaning and disinfection takes place at the end of a production run.

• To re-clean and disinfect after a maximum idle time of cleaned equipment (the time between completion of cleaning and disinfection and when equipment will be put back into operation again).

• To clean and disinfect after commissioning and maintenance interventions

• To minimise the risk of pest infestation.

• To minimise risks to any operators, e.g., from slips (safety).

• To prevent product defects because critical product quality parameters are not met (e.g., colour appearance, taste, size).

• To improve and maintain the operational performance of a production line (efficiency).

• To maintain positive first impressions for staff, visitors, auditing bodies, customers, etc.

• To maintain equipment life cycles.

• To ensure the water for production and all ingredients and food components of the process are controlled in a reasonable manner to prevent any intentional adulteration.

To allow for effective and efficient cleaning regimes, hygienic design should be considered a pre-requisite, such as:

• Access to all surfaces or the hygienic entity can be easily dismantled to enable effective cleaning, disinfection, and inspection routines (disposable parts may be used for components that are not cleanable).

• Use of product contact surface materials that are compatible with the recommended cleaning agents and disinfectants, their concentrations, temperatures, contact times and pH.

Operational elements of a robust cleaning and disinfection programme should include for example:

• Established procedures (SOP) detailing the cleaning and disinfection activities and responsible individuals.

• Validation, verification, and monitoring schemes to confirm the effectiveness of the cleaning regimes applied (see EHEDG Doc. 45).

• The required frequency for routine and periodic cleaning and disinfection protocols to ensure safety while optimising run time efficiencies.

Soil Characteristics

The soiling layers (soils) encountered when cleaning within the food industry can vary widely in composition and structure, giving rise to differences in cleaning mechanisms and their behaviour during cleaning. One way of classifying soil between different food industry processes, with the aim of finding similarities and possibilities of comparison, is to assess fouling mechanisms. Fouling mechanisms described are [20]:

• Reaction fouling - the deposit result from a reaction of some of the components within the food matrix.

• Biological fouling - adhesion and accumulation of microorganisms on surfaces laying a foundation for the propagation of biofilms (for details on biofilms see Appendix 5).

• Crystallisation or precipitation fouling – when a component in the fluid has reached its maximum solubility limit, for example calcium carbonate (CaCO3) when boiling water.

• Particulate fouling – adhesion of particles.

• Corrosion fouling – resulting from the corrosion of a surface.

A combination of the mechanisms mentioned above may result in a more complex fouling process. Examples are protein and calcium phosphate fouling within milk applications and also protein aggregate deposits, which are both a combination of reaction fouling and particulate fouling.

In considering fouling / bio-fouling layer properties, the adhesion and cohesion strengths appear to be the key factors in defining an effective cleaning (and subsequent disinfection) strategy. Hence, an alternative way of categorising soil is by the methods that they are removed during the cleaning process. Fryer and Asteriadou (2009) presented a map of encountered soil within the food industry, their complexity and the method of wet cleaning required for their removal (figure 1).

On the x-axis the complexity of the soil is described, ranging from low to high viscosity fluids. Low viscosity fluids are similar to water in their properties and exemplified with emptying of pipes and tanks containing beer or milk. High viscosity fluids leave layers on the equipment walls, for example, thick starch containing sauces or yoghurts. Cohesive solids are soils behaving like a solid, but their deposits can have very different properties like soft protein gels or hard solid scales from equipment running at ultra-high treatment (UHT) temperatures. The removal of these deposits can be carried out with different cleaning fluids ranging from ambient water, right through to hot water then hot chemicals.

The graph shows three different typical food soils. Type 1 are viscous soils which can be rinsed from a process surface with water (e.g., yoghurt). Type 2 are soils which can be removed by a combination of both water and chemicals (e.g., microbial and gel-like films such as biofilms and polymers). Type 3 are solid-like soils formed during thermal processing (e.g., pasteurisation and evaporation), which mostly require chemicals to be removed. When designing a cleaning program for a specific food production process, it is important to understand the chemical composition of the soil and to select the correct chemicals for its removal. It is important to understand, if the deposited soil is water soluble or not, if it is organic or inorganic, and does it comprise of any protein, fat, minerals, or carbohydrates.

Proteins

Proteins, especially when denatured by heat or an acid, are often difficult food soil types to remove. To dissolve protein deposits, caustic or sodium hydroxide are the most commonly used chemical type. The concentrations required to remove the deposits vary a lot and depend on the origin of the proteins and also the process history. Usually, however, a concentration in the range 0.5-2% w/v Sodium Hydroxide (NaOH) is used.

The addition of wetting agents increases the wettability and suspendability of the protein-based soil. For enhanced cleaning, the use of caustic incorporating oxidising agents (e.g., peroxides or chlorine) which hydrolyse proteins, may be required. However, compatibility with materials used in the processing equipment should be checked prior to use, since some of these chemicals may be corrosive to some materials. Recent attempts to move towards more eco-friendly cleaning strategies have been proposed using enzymes obtained from biotechnological sources.

Figure 1 - cleaning map; a classification of wet cleaning problems based on soil type and cleaning chemical used [20]

Fat / Oil

Fat and oil-based soils are not water-soluble. However, they can be melted and rinsed away to some degree with hot water at temperatures above the melting point of the fat. Cleaning soils that contain fat is most commonly done with alkaline chemicals. When processed at high temperatures over a longer time, a fat-based matrix might change in its consistency due to oxidation, polymerisation or hydrolyzation. This makes the soil more tenacious to remove. Fat and oil can hydrolyse under alkaline conditions. This reaction is called saponification. It results in a solution that has a lower surface tension, better wettability, and increased cleaning effectiveness. This reaction provides the alkaline solution with a lowered surface tension. This is an advantage, however, too much soap generates foam, which may require the use of defoaming agents, especially when using reusable cleaning solutions [7].

Carbohydrates

Simple carbohydrates (e.g., sugar) are soluble in warm water and relatively easy to remove, while for more complex carbohydrate matrices, like starches, mild alkaline or acid cleaners are required. Starches associated with protein or fats require high alkaline chemicals. For starch-based soils often a cleaning sequence commences with an acid and is then followed up by an alkaline solution in a second cleaning stage.

Minerals

Some minerals or inorganic soils are water soluble and can interact with the food matrix during processing. When heating a dairy based product, for example, milk, minerals interact with milk proteins, making the soil more tenacious to remove. Also, inorganic particulate matter may precipitate onto food contact surfaces, especially if surfaces areheattreated(e.g.,mineralscaleinareas withhard water supplies).Toremove mineraldeposits, both organic acids and non-organic acids like nitric acid are very effective. Alkaline cleaning agents may contain sequestering agents, like phosphates and/or polyphosphates, and/or chelating agents (like EDTA,NTA, GLDA, IDS) to avoid the formation of mineral scale deposits. These single stage alkaline products can beused to reduce the frequencies of acid cleans.

Microorganisms

Unwanted biological fouling occurs on the surfaces of heat exchangers, cooling water towers, valves, tubes, sensors, etc. thus increasing the resistance to flow and heat transfer, inducing/enhancing corrosion, which may lead to the contamination of food products [33] For example, in a pasteuriser, some heat resistant bacteria and spores may survive the thermal heat treatment process and adhere to the internal surfaces further downstream. If they are not cleaned correctly or to the correct frequency, then these microorganisms may become very tenacious to remove, especially when biofilms are formed

Two of the microbial species relevant to food contamination are Bacillus cereus and Bacillus subtilis, which are known to develop within foods during storage and have often been responsible for foodborne diseases [31]. They also have a significant ability to adhere to various materials and were found to be resistant to heat and chemicals in milk product processing lines [18], they were also able to survive a CIP procedure. Furthermore, the water used in cleaning operations may itself carry some microorganisms to the equipment surfaces and thereon contribute to the build-up of biofilm.

Therefore, if a surface is not cleaned and disinfected correctly during CIP, microorganisms may contaminate product. During CIP devoted to the whole processing line, biofouling must be removed with the other fouling layers. Caustic detergents are known to be effective for biofilm removal. Previous work has proposed some removal kinetics modelling [28] demonstrating the respective roles of mechanical versus chemical action on biofilm removal [19]. In some cases, alkaline cleaners are insufficient for removing cells and extracellular polymeric substances (EPS - sticky glue-like substances that bind biofilms together and protect microbes from contact with cleaning and disinfection chemicals). In those instances, the use of enzymes can be a good method to break down the EPS structure and thus remove biofilms from surfaces [30].

Wet Cleaning

General

Wet cleaning is usually a matter of applying a solution of a chemical product in water, at a certain temperature, for the required time necessary to dissolve or loosen soil deposits, and the mechanical action of the cleaning fluid aids in the removal these residues. This is visualised by the Sinner Circle (figure 2).

The critical factors that determine cleaning effectiveness are the controllable variables of time of exposure to cleaning solutions, chemical concentration, and thermal energy. Typically, the mechanical action is either given by the design (CIP) or by manual cleaning (hard to control). While a deficiency in one of the energy components may be partially compensated for by an increase in one or more of the other factors, all four are vital to the total cleaning operation. In many cases the chemistry required to effectively remove the soil may be well known, it might not be easy to determine the correct balance of all the cleaning parameters. There is no universal recipe for all cycles and soil types, even if an increase in chemical exposure time, cleaning temperatures or chemical concentrations positively impacts the cleaning effectiveness

The critical factors that determine cleaning effectiveness are the controllable variables of time of exposure to cleaning solutions, chemical concentration, and thermal energy. Typically, the mechanical action is either given by the equipment design and flow rate (during CIP) or by manual cleaning (hard to control). While a deficiency in one of the energy components may be partially compensated for by an increase in one or more of the other factors, all four are vital to the total cleaning operation. However, it might not be easy to determine the correct balance of all the cleaning parameters, as there is no universal recipe for all cycles and soil types

The selection of a cleaning method and the correct cleaning chemical is determined by the soil characteristics, it is therefore critical to understand all influencing factors relative to the soils and cleaning chemicals used. In addition, environmental, effluent treatment and occupational safety aspects should be considered.

All materials of construction shall be compatible with the cleaning chemicals used. Any safety risks when mixing incompatible chemicals, which may occur, should be considered. When designing wet cleaned equipment, it is recommended that equipment manufacturers are working closely together with cleaning chemical suppliers and the end user.

Cleaning Agents

Cleaning agents can range from the use of bulk chemicals, such as sodium hydroxide (also referred to as lye or caustic) and nitric acid, to more complex formulated cleaning products. The use of bulk chemicals is particularly applicable to large food manufacturers and for cleaning less complex, easily removable soils (e.g., raw milk, beer, etc.).

The main active component of all formulated cleaning products is often an alkali or an acid and occasionally enzymes can be used [8]. Additional components such as wetting agents, chelating agents (builders, stoichiometric and threshold sequestrants) and oxidisers can be incorporated to enhance the cleaning efficiency. It is always important to ensure that the dosage and temperature recommendations provided by the chemical supplier are followed and that chemical agents are not used past their expiry date.

Figure 2 – parameters that influence the cleaning performance (Sinner’s Circle)

Bulk chemicals

Bulk chemicals (also referred to as industrial grade chemicals) commonly used are caustic soda (sodium hydroxide, NaOH) and nitric acid (HNO3).

Caustic soda (NaOH) is available in liquid and concentrated form between 30 and 50% w/w and as pellets. 50% w/w sodium hydroxide solutions crystallise at 10-12 °C and are therefore not suitable for storage in cool environments without the appropriate temperature controls (figure 3).

NaOH has excellent properties for the removal of fatty-type soils and protein deposits. As a result of the chemical reaction, water-soluble product residues are formed in e.g., the hydrolysis of fat or the peptisation of proteins. However, as the food soil becomes more complex or more difficult to remove, the cleaning ability of NaOH may need to be enhanced by the addition of other cleaning agents. This is due to the fact that NaOH has a very low impact on the reduction of the surface tension and in the case of high protein residues, high alkalinity can cause the coagulation of proteins at low temperatures.

NaOH based detergents can have a corrosive effect on surfaces, e.g., aluminium, galvanised metal and other soft metal surfaces.

Nitric acid (HNO3) is a strong inorganic acid commonly available as 25 – 60 % w/w solution. It has a low effect on organic soils under normal usage conditions, however it successfully dissolves minerals in deposits originating either from the food itself or as a result of water hardness.

Formulated cleaning chemicals

Formulated cleaning chemicals are prepared by using blends of components to enhance cleaning effectiveness (table 1). Instead of using single formulated products these different components may also be added to a raw chemical on-site.

Figure 3 – phase Diagram NaOH

Components

Examples

Oxidiser hypochlorite, hydrogen peroxide

Complex Formers (Chelatant) EDTA (tetrasodium ethylenediaminetetraacetic acid), GLDA (tetrasodium glutamate diacetate), NTA (trisodium nitrilotriacetate), MGDA (trisodium methyl-glycine diacetate)

Corrosion Inhibitors silicates, amines, carboxylates

Solvents water, alcohols

Surfactants

cationic: quaternary ammonium compounds (QACs), anionic: alkylbenzene sulfonates, non-ionic: ethoxylated aliphatic alcohol, amphoteric: alkyl-betaines

Builders sodium silicate

Enzymes protease, lipase, amylase, cellulase

Most alkaline detergent formulations use NaOH (sodium hydroxide) as the basic ingredient. KOH (potassium hydroxide) can be used in more specialised applications, e.g., to prevent corrosion or to make it easier for the detergent to be rinsed from surfaces.

Acids, including nitric acid (HNO3), phosphoric acid (H3PO4), sulphuric acid (H2SO4), and organic acids (e.g., citric acid) are usually used to dissolve mineral salts, to remove scale formed after an alkaline cleaning cycle and in some cases to aid the removal of mild corrosion on some surface types.

Surfactants, also referred to as wetting agents, are acting at the interface of water-based cleaning solutions and surfaces (residues or material to be cleaned) lowering the surface tension. They also ensure that highly hydrophobic residues, such as oils and fats, are penetrated to facilitate their removal from surfaces. There is a wide range of surfactants available with a diversified range of properties, including the ability to foam, inhibit foam formation, moisten, disinfect, emulsify, or dissolve.

Depending on the charge of their hydrophile group, surfactants can either be cationic, anionic, amphoteric, or non-ionic (figure 4).

cationic

anionic

amphoteric

non-ionic

hydrophile group

Anionic surfactants have high foaming properties, which may be useful in open plant cleaning. Non-ionic surfactants are most frequently used in formulated cleaning chemicals for CIP because they foam less. Cationic surfactants have rather low detergency properties but have high biocidal properties.

Builders (also referred to as dispersants) keep detached residues in suspension and prevent them from settling elsewhere. Builders alone have minimal cleaning performance. However, in combination with other components, such as surfactants, they are capable of enhancing the cleaning effectiveness.

Table 1 - Components in formulated chemicals

Figure 4 – schematics of various surfactants depending on the charge of the hydrophile group

hydrophobe group

Sequestrants and chelating agents prevent the formation of scale. The sequestrant level built into a detergent must be matched to the water hardness and also to any mineral salts that may be present within the soil matrix. They can also have corrosion-inhibiting properties, diffusion, and wetting properties.

Oxidisers convert insoluble organic compounds into soluble polarised ones, which can then be dissolved in the water-based cleaning solution. Oxidisers are also often used when a bleaching effect is required, or where stubborn residues or odours must be eliminated.

Water-insoluble organic substances such as proteins or long-chain polysaccharides (e.g., starch and cellulose) can be easily removed by addition of certain complex formers in the alkaline pH range. Complex formers also dissolve mineral residues and prevent water hardness from having a negative impact on the performance of the cleaning agent.

Corrosion inhibitors, e.g., metasilicates, may have to be incorporate into the cleaning agents, to provide some degree of protection of soft metal surfaces (e.g., aluminium) from corrosion.

Solvents may be aqueous (water) and non-aqueous based. The most common solvent used is water. It may make up the largest percentage of liquid formulated cleaning products. Water adds to the detergency of cleaners as it breaks up the soil matrix, supports the suspension, prevents re-deposition of soils and dissolves watersoluble components, such as sugars.

Non-aqueous solvents such as ethanol and iso-propanol are primarily used for dry cleaning. They have both detergent and disinfectant properties. Other polar solvents may be used for removal of greases and difficult to remove polymerised oils.

Enzymes can hydrolyse organic residues for specific applications, typically in closed equipment (e.g., pasteuriser, pipes, crossflow filtration, and industrial washing machines). Proteases, amylases, and lipases hydrolyse proteins, starch, and lipids, respectively.

Hydrolysation degrades soil into smaller and more soluble fragments. Formulated enzyme-based detergents may contain a blend of different enzymes in combination with other active substances. They are available as powders, liquids, or gels.

The effectiveness of enzymatic cleaning is determined by many factors, such as pH, ionic strength, temperature, composition, and time. Typically, enzyme containing detergents are applied at concentrations of 0.05 - 1% and require pH 7-11 with temperatures of 35-55°C. As enzymes are proteins, they can induce allergic reactions when inhaled and thus may pose a risk for operators, therefore a suitable risk assessment should be carried out before their use.

Concentration of cleaning chemicals

The chemical concentration should be set according to the type of soil and the most difficult part of the processing line or process equipment to clean. Typically, an alkalinity corresponding to 0.5 - 2% w/w NaOH is used for most applications, but higher levels might be required for some applications.

Excessive levels of sodium hydroxide may induce denaturing of components within the food matrix, making them even harder to remove.

Common acids for cleaning are nitric acid and phosphoric acid and are typically used in the concentration range 0.5-1.5% w/w. Higher acid concentrations should be considered with caution, since they may attack polymerbased materials e.g., seals.

Chemical concentrations should be frequently checked to ensure they are being dosed correctly. Under-dosage may lead to poor cleaning performance, over-dosage may not improve cleaning performance and presents a health and safety issue, may lead to equipment surface damage and will also not be cost-effective.

Formulated cleaning chemical concentrates are to be considered as a 100% formulation and the composition of the individual components in the formulated cleaning chemical is usually not revealed by the manufacturer, due to proprietary formulations.

Water Quality Requirements

General water quality requirements are described in EHEDG Doc. 28. Product water shall be of potable quality if the water used is in direct or indirect contact with foodstuffs. At the point of use, the water should meet drinking water requirements. This includes water used for food preparation (washing of food, water as an ingredient), cleaning, disinfection/sanitising, sterilisation, and also hand washing/showering.

The water used should always be fit for the intended purpose. The risks in all steps during storage and distribution should be clearly assessed using HACCP methods. There should be no connection between product (potable) water circuits and circuits holding other non-potable water qualities.

Potable Water is used without additional chemicals for the initial pre-rinse, the detergent rinse, and also the final rinses and may be used for blending with caustic or acid solutions for the cleaning stages. Water acts as a universal solvent for all types of soils, as it is able to dissolve, disperse or suspend inorganic and organic soils. It carries chemicals, energy, and mechanical action to the soils.

The hardness of water used for cleaning is a very important factor to consider. Internationally, hardness is expressed in different units and typically refers to equivalents of Calcium Carbonate, CaCO3, (table 2). For cleaning, disinfection/sanitising and sterilisation, diluent water ideally should be soft. However, the use of too soft water or condensates (e.g., zero mg/l CaCO3 total hardness) is not advisable since it can aggressively leach mineral ions from wetted metal surfaces leading to pitting and corroding. Water with 5-10 mg/l total hardness is ideal and the recommendations provided by the chemical suppliers should be followed.

If hard water is supplied, it may be economical to soften the water. This can be achieved by reverse osmosis systems, zeolite filtration, or other softening systems.

Table 2 – Water Hardness Conversions

Temperature of Cleaning

In general, the higher the temperature of the cleaning solution, the more effective is the cleaning action. However, high temperatures may have an adverse effect if soil characteristics are not considered appropriately. Excessively high temperatures may have a negative impact on the physical and chemical stability of the soil. For example, many proteins are denatured at temperatures above 80°C and potentially much lower, resulting in difficult to remove films. This is especially the case if cleaning is performed at a temperature higher than the temperature used during processing, because in these cases denaturation can be induced during the cleaning stages

Depending on the equipment, the soil and also the cleaning chemical used, cleaning may take place from ambient up to 85ºC. Higher temperatures (e.g., 100–140ºC) are used for example during the alkaline cleaning of parts of UHT plants, such as the holding tube.

Typical cleaning temperatures are:

• Manual clean 40-45 ºC

• Wash-down 50-60 ºC

• Tray Wash 60-80 ºC

• CIP 65-85 ºC

• Boil out 100 ºC

Acid cleaning is usually performed at around 60–70ºC for closed systems and up to 50°C for open plant cleaning. Enzyme based cleaning products cannot be used above the temperature at which the enzyme will be denatured, which often takes place at >55°C [32]

Hot water assists in the emulsification of fats, thus fat melting points should be considered for fat-based soil, for example:

• Lamb 45 – 55 °C

• Beef & Pork 40 – 45 °C

• Poultry > 30 °C

• Butter > 30 °C

• Mayonnaise > 30 °C

• Egg & Blood cold

Mechanical action

Mechanical action is provided by the kinetic energy of the cleaning fluids. The mechanical action dramatically enhances the ability to remove both organic and inorganic materials from wetted surfaces. There are many forms of kinetic energy (described below). Combining these, typically has an incremental benefit to cleaning efficiency when compared to only using one type over a constant period of time.

One form of kinetic energy is friction, such as that created when a surface is scrubbed with a brush, a pad or other abrasive tools during manual cleaning. Another example is liquid jets generated by rotating nozzles or spray balls regularly employed as components of cleaning-in-place (CIP) systems to distribute cleaning solutions and rinsing liquid around the walls of tanks, reactors and other process vessels. Spray nozzles are used for open surface cleaning. Because aerosols can be formed and also water splashing may occur due to the high pressure or wrong nozzle selection, measures to avoid cross-contamination should be taken.

In closed pipe-work systems, the mechanical action is provided by an increase in wall shear stress. It was shown that the soil removal from a surface requires the contribution of both the fluctuating component and the mean value of shear rate [24]

The use of pulsed flow (mainly used for membrane cleaning), where a significant change in velocity is imposed on a steady flow either intermittently or continuously, allows significant changes in the average wall shear stress improving the cleaning effectiveness. Oscillating forces can induce weakening and breaking of the bonds between the soil particles and surfaces [38], [42].

Another mechanical form of kinetic energy is ultra-sonication. It’s a different method used to get “friction” to surfaces not capable of being reached with a brush It’s been demonstrated that ultrasonic pulse waves at one or more frequencies are better than steady state frequencies. Tiny ultrasonic pressure waves create molecular cavitation, with formation and subsequent implosion of micro and nano bubbles at the interface between substrate and foreign contaminant, creating microscopic friction throughout the fluid column. Ultrasoundcleaning was successfully applied to clean crates and small equipment parts. In-place cleaning of conveyor beltmaterials using ultrasound in a thin layer of water is also possible [2]

Using compressed air injection in pipelines has been used for a long time in the dairy industry for large diameter pipes that are too difficult to fill completely during CIP [46]. This method based on a two-phase liquid/air system could be considered as an internal foam cleaning process. Air injection may be done in pulses, in order to increase the mechanical action through a controlled liquid hammering.

Recently, systems have been developed which combine the injections of air to clear and clean pipes, with minimal use of water and chemicals. These systems enhance pipe clearing and product recovery and reduce downtimes during changeovers. Cleaning by injection of small quantities of water into the spinning air stream and subsequent drying by a heated air is possible, with minimal alteration to existing pipework.

Cleaning Agent Contact Time

The cleaning duration is usually set according to empirical criteria (soil characteristics, amount of soil, production run length, surface condition after cleaning, residual contamination when resuming production, etc.). For example, within the dairy industry, it is recommended to clean 40 minutes with an alkaline detergent and 15 minutes with an acid detergent, because thick fouling layers in the heating zones can result in drastic increase in resistance to heat transfer [3]. The cleaning times can even reach several hours for an evaporator clean or a fryer boil out clean [1]

Shorter contact times may require compensating with other parameters (temperature, mechanical action, chemical concentration), e.g., automated tunnel washers.

A simple two-phase model was found to be suitable for describing biofilm removal kinetics during cleaning-inplace of pipes [4]. The first bacterial removal phase would probably correspond to a quick 2-log removal of biofilm matrix and embedded cells lasting less than 3 minutes, while the second phase accounts for removal of cells directly attached to the steel surface. After 25 minutes less than 1-log removal was observed during the second phase. So, most of the cleaning occurs in a very short period of time when compared to the empirical cleaning time in practice. For more information on biofilms see Appendix 5

Selecting the right cleaning agents

The choice of cleaning agents should be made carefully to ensure that soil removal and its dispersion into the cleaning medium, while preventing redeposition on to the cleaned surfaces, are fully achieved. Also, environmental, and operational impacts should be considered.

Detergents can be evaluated as suitable, if the desired level of cleanliness can be achieved (taking into account type of soils present and the manner in which the soil is formed) and if the chemical is compatible with the plant materials, equipment design and the cleaning methods available. In order to do that, the formulation of the cleaning agents should be closely scrutinised using product specification, written documentation, and technical knowledge.

The most objective method for testing the suitability of detergents is to trial them through a standardised, laboratory approach. This involves applying relevant soils to coupons made of the same material as that found in the process equipment and then measuring the cleaning effect by visual inspection, weight loss (pre- and post-clean) and/or by Total Organic Carbon (TOC) analysis. Once this is complete, it is possible to test the remaining prospective formulations in the factory on difficult to clean processing equipment in order to get realistic, industrial scale results. After this point, and as the final part of the decision-making process, operational aspects like cleaning efficiency versus cost and after sales service levels should be considered.

Cleaning-in-Place (CIP)

CIP can be defined as the cleaning of internal surfaces of closed equipment, complete items of a plant or pipeline circuits without dismantling or opening of the equipment and with little or no manual involvement from an operator. The process involves the jetting or spraying of surfaces or the circulation of cleaning solutions in a closed loop of the plant under conditions of increased turbulence and flow velocity.

The critical parameters that are impacting cleaning performance as per the Sinner’s cycle shown in figure 2 should be determined for each circuit individually. A fully automated CIP system control set points for flow, temperatures, concentrations, and duration of each CIP step.

The mechanical action inside pipelines is provided by shear forces from the flow of the fluid. As a rule of thumb, the flow must be turbulent, and the mean flow velocity should be at least 1.5 m/s to achieve an adequate mechanical force.

Due to variables, such as soil characteristics, conditions of the surface to be cleaned, the set points of the other cleaning parameters, etc., higher velocities might be required to achieve good CIP results. However, lower velocities also could be sufficient. This should be evaluated during the cleaning validation process.

The mechanical action required for tank cleaning is provided by the spray devices (spray balls, rotary spray or jetting devices).

CIP processes within the fermentation and brewery industries are mainly based on acid cleaning practices, as carbon dioxide generated during the fermentative process will rapidly convert the NaOH (caustic) present in alkaline cleaning agents to Sodium Carbonate (Na2CO3). This Na2CO3 can quickly precipitate as processgenerated scale, while the loss of CO2 can create an under-pressure within the fermenter, increasing the risk for reactor implosion.

For more details refer to EHEDG Doc. 50.

Open-Plant- Cleaning (OPC)

General

Foam cleaning is the preferred method for effective and efficient cleaning of large accessible areas, such as interior and exterior surfaces of machines, walls, and floors. Typically, a low/medium-pressure foam process is applied, which generates foam by pushing a concentrated detergent solution, water, and air through a nozzle.

Cleaning by means of a low/medium-pressure foam processes provides many advantages in comparison to high-pressure cleaning. High-pressure cleaning processes are not recommended for the food industry, since they generate aerosols, which can spread pathogens, spoilage organisms, soil and cleaning agent residues. These aerosols may contaminate exposed product within the manufacturing environment.

The low/medium-pressure foam process reduces aerosol formation, protects mechanically sensitive materials, ensures a safe working environment for operators, and leads to successful hygienic results.

When foam is generated the volume of the liquid phase is increased by approximately 500 times the initial volume of the detergent concentrate. This is done by injecting air into the solution of cleaning agents. Depending on the detergent formulation, various foam qualities can be produced for the various applications. In principle, cleaning foams can be divided into five categories of foam types, selectable based on a range of different requirements (table 3):

• Classic foam.

• Quick break foam - a stable, slow draining foam detergent which reduces soil deposition and disperses easily on rinsing.

• Gel foam - on dilution with water, a “thixotropic” gel is formed which adheres strongly to surfaces and so increases the contact time for penetration of heavy soils. Can be applied as an aerated gel (foamgel) or as a conventional gel.

• Long cling (LC) foam - advanced stable foam to provide enhanced cling to vertical and smooth surfaces.

• Thin film cleaning (TFC) foam – a foam designed for tenacious soils and applied as a thin layer of foam.

Table 3 - Comparison of Foam Cleaning Systems

Criteria Classic foam Quick break foam Gelfoam Long cling foam Thin film foam

Degree of soiling medium medium medium high tenacious high tenacious

Requirements for prerinse (medium to high soiledsurfaces) thorough thorough thorough short short

Typicalcontact time(no visible foam on treated surfaces after application) 10-30 minutes

Releaseoftheactive, liquidcleaning phase fast fast slow continuously slowed down continuously slightly slowed down

Object/surfacearea small to medium small to medium preferable large preferable large small to medium

Rinseproperties fast very fast extended slightly extended fast

Suitabilityforcentralised, prediluted systems? yes yes no yes yes

Suitability for automatic cleaning (e.g., conveyors, filler) yes yes no no yes

Various systems are available for foam generation. They are divided into centralised pressure systems, decentralised foam stations and mobile foam systems.

Centralised pressure systems

Centralised cleaning systems allow a factory or site to have access to low, medium or high pressure wash down facilities fed from a single area (figure 5). This reduces operator misuse and allows strict control of detergents and disinfectants, making them ideal for high-hygiene areas. This type of system is typically supplied from bulk chemical tanks or intermediate bulk containers (IBCs). The detergents and disinfectants are pre-diluted within a dedicated area, typically located away from food manufacturing areas, and the pump supply the pressure to distribute rinse water and diluted detergent and disinfectant to several satellites which are strategically located around the factory. The chemical satellites have a compressed air feed for foam generation and for operating actuator selection valves on the satellites. The operator selects the correct nozzle for the rinsing, foaming or the application of disinfectant

The system allows different departments and several operators to clean simultaneously and thus eliminates the requirement to have concentrated chemical containers within manufacturing areas. This type of system also simplifies chemical concentration checks as they only need to be checked at the point of dilution. A centralised system requires individual lengths of pipework for rinse water, detergent, and disinfectant, therefore making it a significant investment.

Decentralised pressure systems

A decentralised system installation involves installing less pipework (figure 6). Detergents and disinfectants are diluted at the point of use within individual chemical satellites. The system is pressurised from a central point (a booster satellite) and the installation only requires a ring main pipework system to distribute water to every point across the site, which involves less capital expenditure when compared to a centralised pressure system. Compressed air is still required at every satellite point for foam generation and the operation of the air operated actuator selection valves.

This type of system does have a greater degree of flexibility, when compared to a centralised system. If the site decides to change their detergent or disinfectant at the point of use, only the point of use need to be flushed through with clean water, rather than the entire system.

Figure 5 – centralised system (courtesy of System Cleaners)

Figure 6 – decentralised system (courtesy of System Cleaners)

Portable Foam Application Systems

There are several portable foam application systems available on the market (figure 7 and 8). These systems require significantly less investment when compared to the centralised and decentralised systems.

The portable systems can be pressurised with compressed air or they can be non-pressurised, where the air supply drives an on-board pump. With these types of portable systems, the reservoirs are filled with pre-diluted foam detergent solution and are then connected to a compressed air supply. The consistency of the foam can be adjusted with simple adjustment valves.

There are also options for medium- and high-pressure water ring main supply sites. For medium-pressure water ring main systems, a portable unit can be connected to chemical containers filled with foam detergent held within the main body of the unit. Portable systems require compressed air and an electrical supply for the booster pump. The compressed air and the booster pump increase the outlet water pressure.

For high-pressure systems, foam can be generated via the use of stainless-steel injectors and a separate foam lance. The chemical strength of the diluted detergent foam is controlled by the insertion of an orifice plate into a chemical inlet side on the injector. The high-pressure lances draw air through the lance to help create the foam.

A further distinction is made between static CIP foam systems where cleaning is carried out using nozzles in a fixed position and semi-automatic processes (those described above). For static CIP foam systems (e.g., used for beverage fillers or conveyor belts) the cleaning is carried out with little involvement of personnel. Specific nozzles are available for the different cleaning steps and application areas. This includes rinsing nozzles and foam nozzles with different flow capacity and spray angle.

Figure 7 – examples of various portable systems

Working Principle

Of the four basic components of the Sinner circle, only time and chemicals are relevant during the foam stage. The heat transferred from foam to large surfaces is negligible. Any cleaning effect and chemical reaction takes place at the temperature of the surface being cleaned. This can be a severe limitation in refrigerated environments e.g., in meat or seafood processing, where fatty residues cannot be melted. The only mechanical influences come from the slow movement of the foam structure on vertical surfaces and the local effect of collapsing foam bubbles. Dwelling time is commonly around 20 minutes for each foam application step. Shorter time spans are usually not sufficient to loosen the soil structures. Longer interaction leads to drying, which can re-arrange and re-solidify the residues. Reorganisation can lead to more tenacious soiling than originally encountered.

Rinsing removes the soil weakened by the chemical attack from the foam components. Here, mechanical and temperature effects play an important role. To achieve sufficient impact, overall application pressure can be increased. But it is more common to switch to specific nozzles and to remain at the same system pressure. The increased mass flow during the rinsing allows for the transfer of enough heat to partially melt fatty residues and when mixed with the detergent from the foam, this helps to emulsify and remove fats.

Chemicals that enhance the cleaning properties are formulated within the detergent base for the foam. These active ingredients consist of the same chemical classes as discussed in chapter 6.2 (e.g., alkali, acids, complexing agents, enzymes). As with all other cleaning techniques, the properties of the soil to be removed determine the choice for the most effective active ingredients. The interaction between detergent system, active cleaning ingredients, nozzle design, water quality and air pressure determine the foam properties.

The ideal foam cleaner is stable in concentrated form for several years at ambient temperatures. Ideally, the foam generated (figure 9) upon use

• will be stable

• will have good visibility to indicate that it has been applied evenly and on to the whole surface

• adheres strongly even to vertical structures

• does not dry out over the dwelling time (typically 10 - 20 minutes).

After use, the foam should allow for being rinsed off easily, should exhibit only minimal foaming tendencies within the effluent process and should be capable of being easily degraded within the wastewater treatment plant.

Figure 8 - foam application using a mobile system (courtesy of Ecolab)

The reactivity of active cleaning agents (e.g., the combination of strong alkali and active chlorine) severely restricts the choice of any suitable surfactants. The structures formed can be described in the terms of bubbles (the loose parts) and gels (the denser parts). Depending on application, the properties of more dense or looser foams can be advantageous. A standard foam of a 500 litre volume typically consists of 1 kg of concentrate, 49 kg of water and 450 litres of air This volume allows the effective cleaning of 170-250 m2 of surface area.

The foam bubbles, which disintegrate dynamically during the reaction time, provide the liquid active phase to the surface. The cleaning effect of the foam first takes place at the interface between the cleaning phase and the impurity. Subsequently, the cleaning solution penetrates into the residue. Overall, the reaction time is significantly increased compared to spraying processes. The dissolved impurities can then be finally rinsed off from the surfaces.

Cleaning Procedure

A cleaning and disinfection programme that has been appropriately validated and implemented will be effective at reducing or removing hazards (microorganisms, chemical residues, physical contaminants, and allergens) to an acceptable level.

The cleaning programme needs to be scheduled correctly to ensure hazards are effectively removed or reduced to an acceptable level from the food manufacturing environment, rather than being moved from one surface to another (e.g., from the floor to food contact surfaces) by, for example, aerosols from cleaning sprays.

The cleaning programme should also be documented on a cleaning instruction card or standard operating procedure (SOP) and this should be trained out to all personnel who are involved with the cleaning.

To obtain an excellent standard of cleanliness, the food processor should employ a structured cleaning and disinfection protocol and consider the following sequenced activities when developing a procedure for open plant cleaning. Depending on design of the object to be cleaned and the expected level of cleanliness not all cleaning and disinfection steps might be required (table 6): 1.

8.

Detailed guidelines on OPC procedures can be found in Appendix 3.

Figure 9 - foam structure, classical foam cleaner

7

Cleaning-out-of-Place (COP)

Some parts of equipment cannot be cleaned in situ and thus require partial or complete dismantling for cleaning them out of place. Out-of-place cleaning systems include for example equipment washers (for process equipment and containers), soaking tubs/tanks, sinks, mould/crate washers, cabinet washers, and ultrasonic cleaning devices. COP operations may be fully automated, semi-automated, or done manually. Common to all these systems is that the same factors and parameters discussed in the previous chapters, such as temperature, chemical action, mechanical actions and time, are critical for the cleaning effectiveness. Though theoretically COP operations also comprise dry cleaning as well, it is commonly referred to as a wet cleaning method.

Depending on the user’s hygiene requirements it is necessary to evaluate and decide if re-circulation of wash water or the re-use of rinse water is appropriate. As with CIP, some COP systems collect and re-use the final rinse water for the next pre-rinse or wash. This can become quite a challenge if the washing efficacy is not optimised. In this case, the rinse water may contain microorganisms and/or allergens that are carried over to the next batch. Therefore, it is important to continuously check the quality of the pre-rinse / wash water.

For manual operations (e.g., soak tank, scrubbing in a sink) parameter values are not automatically controlled and recorded. However, for automatic or semi-automatic systems (e.g., mould washers, COP equipment washers with or without circulation, figure 12 and 13) these are usually equipped with sensors and transmitters for pausing /holding the system or raising alarms, if critical parameter values are not met and for capturing data. The lower the level of automation, the more the cleaning effectiveness depends on the skills of the cleaning personnel. Thus, thorough training of operators is critically important and depending on the sensitivity of products manufactured, validation, verification and monitoring programs of the cleaning effectiveness may be required. When using COP, the complete coverage with mechanical action from the cleaning fluid on all the areas to be cleaned is critical. If not hygienically designed, systems may lack appropriate coverage with mechanical action resulting in poor cleaning effectiveness. Placement objects within the equipment washer also impacts the degreeof coverage with mechanical action on the surfaces to be cleaned. For example, an object may be placed onto racks with appropriate nozzles distributing the cleaning fluids through hollow equipment (figure 10) or placed on shelves (loose or fixed, figure 11).

Racks are typically cleaned along with the equipment, thus eliminating the risk of cross contamination of cleaned equipment from a “dirty” rack.

Table 6 – Typical standard cleaning protocols

The basic steps for a manual operation may include:

• Dismantling

• Gross debris removal (recommended)

• Low pressure pre-rinse

• Soak and physical agitation with a suitable cleaning agent

• Post-rinse to remove residual cleaning chemicals.

• Drying (optional)

• Conduct pre-operational inspections (optional disinfection)

• Re-assemble the equipment.

• Disinfect the re-assembled equipment (optional).

The basic steps for an automated operation may include:

• Dismantling

• Gross debris removal (recommended)

• Low pressure pre-rinse (optional)

• Loading of objects to be cleaned into equipment washer

• Selection of wash programme according to procedure

• Drying (optional)

• Conduct post-cleaning inspections (disinfection optional)

• Re-assemble the equipment.

• Disinfect the re-assembled equipment (optional)

Figure 10 - Rack with fixtures and nozzles for process equipment

Figure 11 - Rack with weighing equipment on shelves

Dry Cleaning

General

Dry cleaning refers to methods where no aqueous detergent solutions or aqueous suspensions are used It is common practice to also include methods which allow for the use of a limited amount of water, such as wet wipes or dry steam (see 7.2.7). This method is also referred to as controlled wet cleaning to distinguish from wet cleaning using unlimited amounts of cleaning fluid (also referred to as wash down). For controlled wet cleaning, critical limits should be established for the amount of water used based on a hazard analysis. However, it is vital that any residue of moisture is removed completely before the equipment is put back into service.

Typically, dry equipment cleaning is the method of choice for low moisture products with a water activity of aw < 0.6, where even small amounts of moisture may cause microbiological, quality, or operational issues and thus wet cleaning may result in food safety risks. On the other hand, very often fine dust is formed during the manufacturing process of low moisture products, which might be not easy to remove from product contact areas and the exterior of equipment. This fine dust can be a safety concern in the presence of an ignition source that can trigger an explosion. When selecting the appropriate dry-cleaning method, not only effective and efficient removal of soil and debris should be considered, but also safety aspects are critically important e.g., ATEX certificated vacuum cleaners. [34], [35].

Figure 12 - Examples of COP baths

Figure 13 - Example of a COP Equipment Washer / Disinfector

Techniques and Tools

Wipes

Wiping or sweeping is commonly used to remove loose soil deposits from a surface. Suitable colour coded disposable wipes with sufficient strength and absorbency should be used as opposed to the multiple use of rags. Wiping should only be done on relatively small surfaces and for minor spillages as it is very labour intense. Thus, it is typically done after gross soil removal by means of scraping or brushing.

For keeping the surface completely dry, alcohol (e.g., isopropanol) based wipes should be applied. Even if destroying a wide spectrum of bacteria is not required, alcohol is a good solvent and facilitates cleaning and drying.

Scrapers

Scrapers work on the principle of dragging a firmly pressed scraper over a surface and lifting dried or baked-onsoils from the surface by friction.

Care should be taken that the scraper blade is made of a compatible material which does not become damaged or which may damage the surface being cleaned (scratching). Ideally the scraper should be moulded into one single piece, made of solid plastic, e.g., polypropylene (figure 14).

Brushes

Brushes work on the principle of dragging bristles over a surface and lifting the soil deposits from them by friction between the brush bristle and the surface. The effectiveness of the mechanical removal of loosely adhered soil and debris depend on the length and type of the bristles, as well as the mechanical force an operator can provide. Brushing may create clouds of dust, which can be minimised, if the brush head is being pulled towards the operator (rather than pushed away from them). Brushing should not be applied in areas with a high risk of explosion. Also, loose bristles may result in foreign material contamination risks, therefore, bristles should be sealed into the brush head to ensure they are secure and to also enable the item can be fully cleaned and disinfected (figure 15).

Figure 14 – metal scrapers may damage surfaces and should not be used. Scrapers moulded in one piece are preferred (photo on the right courtesy of Vikan)

Compressed air cleaning work principle is that it removes soil from surfaces by providing kinetic energy, after which it can move from one area or environment to another, where it may resettle. Removed soil needs to be picked up using a brush and dustpan or vacuum system.

As the pressure of compressed air in a plant can be up to 10x105 Pa, only appropriately designed air guns, taking health and safety risks into account (risk of injury, noise level) should be used. In environments with dust explosion risk (e.g., flour mills) compressed air should not be used.

As compressed air disperses soil and debris which may lead to microbiological, physical (foreign materials), or chemical (allergens) airborne contamination risks, its use should be limited to contained areas. Also, compressed air can hinder cleaning by blasting debris further into the equipment. For those situations compressed air should not be used.

If the use of compressed air cannot be avoided, the quality of the air should meet the same level as defined by the plant air for food contact based in ISO 8573-1 [23]. In particular, attention should be paid to the degree of drying of the compressed air to ensure there is no moisture in it. Drying to a dew point of e.g., 20°C below the lowest temperature the compressed air lines should be exposed to is thought to be sufficient to prevent moisture condensing in air lines.

Vacuum Cleaning

Vacuum cleaning works on the principle that it removes loosely adhered soil from a surface by suction. Light and moderate accumulations (dirt, dust) can be lifted from both smooth and irregular surfaces and transferred via a vacuum hose into the central system or portable collection unit (figure 16). Specially designed portable units are also capable of collecting wet dirt or even water.

Compressed Air

Figure 15 – hygienic brush (courtesy of Vikan)

Figure 16 – central vacuum cleaning system (courtesy of Daxner international) and a portable unit (courtesy of Nilfisk-Advance, Inc).

Vacuum cleaners and their parts, (tools, nozzles, brushes, hose, pipework, etc.) should be dedicated to the hygiene zones present in the factory. Vacuum cleaners should be cleaned regularly and well maintained to avoid

any contamination risks. Keeping a central system in a good condition is usually more challenging than a small portable system.

Vacuum cleaners are typically equipped with a multi-stage filtration system. Filters should be changed regularly to achieve a constant airflow. Exhaust filters meeting the HEPA/ULPA standard may reduce the risk of dust explosion and microbiological contamination.

Dust and dirt should be collected using dust containers or dust bags. The disposal of dust should be managed in a controlled way so that re-contamination risks are minimised. Regular cleaning of vacuum systems to prevent pest infestation is also recommended.

Dry Ice

Dry ice is the solid state of carbon dioxide (CO2) which can be used for the removal of baked-on or caked-on residues. The cleaning effect is due to the impact of carbon dioxide pellets hitting the surface at temperatures of -43°C to – 26°C at very high speeds which penetrate into the soil and finally loosen the soil by friction and sublimation of the CO2 from a solid into a gas (figure 17). This sublimation process proceeds with an explosive change in volume, lifting and loosening the residue from the surface being treated. The conversion of solid into gas (carbon dioxide) is a process partially taking the energy needed from the surface treated and these surfaces will then cool down.

Dry ice cleaning is a very effective, non-toxic method for removing hard to clean non-elastic soils. Even grease, glue or paint can be removed. However, safety aspects need to be taken into consideration. The process can be very noisy, and the operating temperature is very low (gloves are required for hand protection). Masks should be worn to protect the eyes and nose in dusty areas. The area where dry ice cleaning is applied requires effective ventilation to vent the CO2 gas formed, so it might be that this method has limitations in small, confined spaces.

As with compressed air cleaning, soil is spread around, and the removed soil needs to be collected after the application of dry ice. Minor amounts of condensation may occur, and any moisture should be removed immediately. The abrasive method may alter the surfaces of equipment, so care should be taken that this method is compatible with the materials of construction.

Dry Steam

Dry steam cleaning works on the principle that when heated under pressure of approximately 10x105 Pa to a high temperature (e.g., 180°C) steam becomes superheated. The moisture level at this temperature/pressure will be at approx. 3 - 5% due to condensation on the surfaces treated. The steam travels from the heater through an insulated hose at its tip. Only the temperature at the tip is high and will loosen the dirt and soil on the surface, which must be wiped or vacuumed off.

Dry steam cleaning can be an alternative for cleaning equipment or areas that do not allow for wash downs. Mobile devices are available with different tools as well as stationary belt cleaners. It can be operated without chemicals (de-greaser might eventually be sprayed onto the surface before dry steam is applied) and very little moisture, which can be removed by integrated vacuum cleaners. It is very useful for small, slotted profiles, shaped surfaces, crevices, seams, etc., which are usually difficult to access.

Figure 17 - dry ice blasting cleans and removes most soils from product contact and non-product contact surfaces when the working distance is less than 200 mm (courtesy of Blackwell’s Inc.)

Dry steam cleaning can also reduce microbiological loading.

Heavily soiled areas require scraping and/or brushing before the dry steam cleaning process is applied.

Push Through / Purging

Material flushing can be applied for closed manufacturing equipment and is typically done during product change overs of low moisture or dry products. A predetermined, validated quantity of flushing material is pushed through the system. The flushing material can be the subsequent product following the previously run product or an inert material compatible with the product produced after the flushing procedure, usually materials used as part of the recipe. For dry material handling systems abrasive materials, like sugar, salt, rice, might be the right choice. Material flushing can be used in pneumatic conveyance systems or within closed pipework where the product is just pumped. It needs to be considered that the cleaning effectiveness is not comparable to wet cleaning, as some residue (e.g., allergens) always remain within the system. This method is rather a dilution down to an acceptable level method of cleaning.

‘Pigging’

When pigging is employed, solid plugs (‘pigs’) are used to clean pipelines. This method is considered as a drycleaning method but is also often used in combination with CIP (then solid plugs or crushed ice is used) and material flushing for recovery of product. Pigging may also minimise the mixing of phases. It may also be used for separating batches of products.

Conventional pigging is limited in the pipeline design to which it can be applied, as it typically requires a certain radius of bends, very smooth internal surfaces, and a constant inner pipe diameter slightly larger than the plug throughout the section of the pipework to be cleaned.

The plugs should be solid and made of one-piece, contoured rubber. Besides the plug, a pigging system requiresa device to launch and send the plug and a receiver to catch it. Fully automated systems are able to send the plug back to the launch device and the plugs are equipped with a magnetic core to detect it. The launch deviceneeds to provide the media that pushes the plug through the pipeline. This media may be compressed filtered air, another inert food grade gas, or a compatible material used for material flushing. Cleaning of the sending and receiving devices, as well as the plug itself need to be considered when designing and operating these systems.

Disinfection

General

Though effective cleaning may significantly reduce the microbial load, disinfection is applied subsequently to reduce levels further to a point that is considered safe from a product safety (pathogens, toxin forming microorganisms) and product quality (spoilage organisms) perspective. Disinfection should only be initiated on visually clean surfaces. Remaining deposits may hinder the accessibility of microorganisms by the disinfectant solution. Residues may also react with the active ingredients of the disinfectant. In this case, active substances are no longer able to eliminate microorganisms and the disinfecting efficacy may be greatly reduced. Hence, meeting hygienic design criteria detailed in EHEDG document N° 8 are critically important to achieve effective cleaning and disinfection results.

Disinfection should only be used based on a risk assessment. If disinfection is deemed to be necessary, then the following areas should be considered:

• Food contact surfaces (direct/indirect)

• Human machine interface surfaces (HMI)

• Cleaning materials and equipment

• Hands, footwear and gloves

• Environmental air

• Drains, troughs, floors

• Condensate drip pan and drain lines from refrigeration coils

• Wheels on racks, carts and forklifts

Disinfection methods can be divided into chemical and physical disinfection.

Chemical Disinfection

Chemical disinfectants, also called biocides, are defined by their mode of action, and can be broadly split into two groups, oxidising, and non-oxidising.

Oxidising disinfectants such as hypochlorite solutions, peracetic acid, and hydrogen peroxide attack all cellular material and stop the micro-organism from functioning.

Non-oxidising disinfectants such as Quaternary Ammonium Compounds (QACs), Biguanides and Amphoterics or Triamines penetrate the cell wall and disturb the phospholipid molecules which make up the bacterial cell membrane; they then block metabolic pathways required for the organism to survive and /or cause it to leak vital cellular content. Either way the organism dies.

Ideally chemical disinfectants should be automatically dosed via a compatible dosing unit to ensure that they are used at the correct strength. If disinfectants are used correctly at their required strengths, contact times, and applied correctly in accordance with the manufacturer’s instructions, there is no scientific evidence that microorganisms develop resistance to biocides. Rinsing significantly reduces the level of chemical residues remaining on cleaned and/or disinfected surfaces, and therefore the likelihood that these residues may subsequently enter the food. Rinsing of food contact surfaces post disinfection/cleaning is a recommended approach to ensure minimisation of food contamination, no matter the make-up of the cleaner, disinfectant, or material in question.

Legal Requirements

Europe: The Biocide Regulation (EU) No 528/2012

Biocides are by definition of the European Parliament preparations containing one or more active substances which are intended to destroy or inactivate harmful organisms by chemical or biological measures. On September 1st, 2014 the biocide directive (EU) No 528/2012 of the European Parliament and of the Council came into force. The biocide regulation represents a milestone for the evaluation of disinfectants, as they are also used in food processing. Primarily, there are two objectives in focus: the protection of human health and the environment. Biocides that don’t meet these requirements may no longer be marketed in the future. The European Chemicals Agency (ECHA) coordinates this new European approval process ('Union authorisation').

In selecting appropriate test methods for disinfectants that are to be used in the fields of food processing, the choice for the manufacturers of biocides as to which microbiological test methods can be used is not optional. The biocide regulation demands that the effectiveness of biocidal products must be demonstrated against defined target organisms. For that purpose, microbiological European standards (EN-Test methods) for disinfectants were developed in collaboration with the European national standards bodies. These standards takeintoaccount influences due to differences in the effectiveness of biocides under real and practical conditions.These specific European test methods highlight the current state of technology.

In the European standard tests, the biocides undergo multistage test phases. The effectiveness tests are designed so that high safety margins for possible application errors are provided. The addition of the term ‘low organic load’, even under "clean conditions", is taking into account that even with good cleaning small residues can be left on the surfaces. If disinfectants are used on not completely cleaned surfaces (e.g., for combined detergent-disinfection regimes), they should be examined by the EN standards under "dirty conditions".

The tests are carried out respectively towards defined, different test organisms, so-called reference strains, which are chosen for their known resistance to disinfectants. By using examples of different microbial species with high disinfection resistance, it is assumed that the results from disinfectant tests using these reference strains are applicable to all microorganisms in their broad category (bacteria, fungi, viruses etc.) which are likely to be found in food processing environments. The EN standard includes different test phases to provide decisive evidence of the effectiveness of a disinfectant. These laboratory tests are conducted under practical conditions. Here different exposure times and test temperatures are tested with and without organic loads:

• EN 13704 - Testing of sporicidal activity of disinfectants used in food areas against bacterial spores [11].

• EN 1276 - Testing of bactericidal activity of disinfectants used in food areas against bacteria [12].

• EN 1650 - Testing of fungicidal activity of disinfectants used in food areas against yeasts and moulds [13].

• EN 14476 - Testing of virucidal activity in the medical area against viruses [9].

Furthermore, a surface test of high significance is defined particularly to demonstrate disinfection efficacy in open systems. This simulates the effectiveness on contaminated surfaces in practice:

• EN 13697 - Quantitative non-porous surface test for the evaluation of bactericidal and/or fungicidal activity of chemical disinfectants used in food [10].

The practical consideration of "protein error" by the addition of a low soil condition even in the so-called "clean conditions" is obligatory for these tests. With these tests, the irreversible inactivation of non-dried and dried-on microorganisms on surfaces is covered.

United States

United States Food and Drug Administration (US FDA)

The FDA is a scientific regulatory agency responsible for the safety of food in the United States, either domestically produced or imported. Specifically, the FDA is the federal agency responsible for ensuring that foods are safe, wholesome and of high quality. The FDA also supervises the safety and effectivity of human and veterinary drugs, biological products, medical devices, cosmetics, as well as electronic products that emit radiation. Products must be honestly, accurately, and informatively represented to the public. US FDA regulations are found in Title 21 of the publicly available Code of Federal Regulations (CFR). The FDA “does not register or issue certificates of authorization, or approvals of any kind, for specific products intended to be marketed as food additives in the US”. Their role in the regulatory process is to review the safety and issue regulations stipulating conditions of safe use for chemicals intended to be components of food.

United States Environmental Protection Agency (US EPA)

The US EPA is a regulatory agency with the mission to protect human health and the environment. As part of this mission, it is responsible for reviewing and registering pesticides sold in the United States in accordance with the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). Disinfectants are listed under pesticides and examples of pesticides subject to FIFRA registration also include, but not limited to, no rinse food contact surface sanitiser chemicals and preservatives. Only those products sold in the US that make pesticide claims have a registration with the US EPA. US EPA regulations are found in Title 40 of the CFR.

NSF International

NSF International is a not-for-profit, non-governmental organisation (NGO) and undertakes standards development, product certification, education and risk-management for public health and safety. NSF International launched its Non-food Compounds Registration Program in 1999 to re-introduce the previous authorisation program administered by the USDA. Unlike the USDA program it is a voluntary program and is available to manufacturers across the globe. Products eligible for NSF Registration under this program include all compounds used in and around food establishments, such as disinfectants, lubricants products used for preprocessing of food like fruits, and the disinfection of vegetables. In addition, NSF Registered products are permitted to carry an NSF Registration Mark on the product label and are identified in the publicly available NSF White Book™ Listing of proprietary substances and non-food compounds.

Canada

Canadian Food Inspection Agency (CFIA) is “dedicated to safeguarding food, animals and plants, which enhances the health and well- being of Canada's people, environment and economy.” It was created in 1997 and is the Canadian counterpart of the USDA’s FSIS. The CFIA enforces the policies and standards set by Health Canada (which is responsible for establishing policies and standards related to the safety and nutritional quality of all food sold in Canada). The assessment for use of non-food chemicals within food processing and preparation operations generally falls under the purview of the CFIA (in the cases of those Federally registered and inspected operations) and the Chemical Health Hazard Assessment Division of the Bureau of Chemical Safety – Health Canada. The assessment performed by the Bureau of Chemical Safety takes into consideration the potential for incidental contamination of food by the use of the proposed product and given the known or presumed toxicological profile of the material, whether that presents an acceptable risk. Manufacturers of nonfood chemicals submit the information on their products along with the proposed use and receive – if found acceptable – a letter of no-objection (LONO) from the Bureau. This letter, publicly available on the internet, indicates that the product can be sold in Canada for the uses listed in the submission.

International/national legislation dealing with removal of chemical disinfectants

There are regional differences, but in general it can be advised that all chemicals should be rinsed from surfaces after use. Rinsing significantly reduces the level of chemical residues remaining on cleaned and/or disinfected surfaces, and therefore the likelihood that these residues may subsequently enter the food. The reduction is further increased if warm water is used. Rinsing of food contact surfaces post disinfection/cleaning is a recommended best practise approach to ensure minimisation of food contamination, no matter the make-up of the cleaner, disinfectant or material in question. The remaining residuals that may contaminate or adulterate food contacting cleaned surfaces are expected to be minimal, or negligible, following a potable water rinse. Therefore, the potential ingestion of residues resulting from the approved use of these types of products does not represent a significant health hazard under the intended conditions.

The Codex Alimentarius – section 6.1.2 – General Principles of Food Hygiene states that disinfection must be followed by rinsing unless the manufacturer’s instruction (product label) indicates on a scientific basis that rinsing is not required. Some countries have legal requirements for registering a disinfectant and need to mention this on their labels (e.g., EU).

In France for instance, the law specifies which surfaces (food contact or non-food contact) in which applications need rinsing after final disinfection, but other countries (e.g., Belgium, the Netherlands, and Italy) don’t specify these surfaces, so everything needs to be finally rinsed, unless otherwise stated, with a specific non-rinse claim.

The UK did not have legislation that requires the registration of disinfectants (before final Biocidal Products Directive, BPD, implementation) and subsequently regarding this, suppliers do not have to mention anything on their labels.

The Control of Substances Hazardous to Health (COSHH) mentions that the operators should follow the directions on the labels.

In the UK rinsing is not routinely undertaken in the manufacture of ready-to-eat food products. In these food processing operations, the balance of residue absorbance into food products is thought of as less of a risk than the addition of water to surfaces during rinsing (which may contain microorganisms) and the associated additional time for the food processing equipment to thoroughly dry (wet equipment encourages pathogen growth and spread), together with the potential benefit of residual, surface antimicrobial activity. In such circumstances, disinfectants are also tested to ensure that any residues left on surfaces are unlikely to cause organoleptic changes in subsequent food products processed on the line.

The FDA (US) disallows a rinsing step after final disinfection for non-rinse disinfectants if they are registered as such with the US Environmental Protection Agency (EPA). EPA sanitisers are no-rinse in the US.

Oxidising Disinfectants

Sodium Hypochlorite (NaOCl)

NaOCl is the most common form of chlorine disinfectant available.

Today sodium hypochlorite is almost only produced using the so-called electrolysis process. The hypochlorous acid generated on the anode side is alkalized with sodium hydroxide solution, whereby NaOCl is formed. When used correctly, NaOCl belongs to the group of the most suitable biocidal actives for the food industry.

The most important reaction of sodium hypochlorite is the oxidation of organic and inorganic compounds with the formation of oxidation products and chloride ions. The oxidation causes about 99% of the active chlorine to react to form chloride ions. The oxidation of organic material forms the basis for the disinfectant effect of cleaning agents or disinfectants based on sodium hypochlorite. A much lower percentage also results in the halogenation of organic compounds, which can be recorded as AOX (Adsorbable Organic Halogen Compounds). Sodium hypochlorite is therefore a strongly oxidising compound that forms various reaction products when used, that finally end in wastewater.

NaOCl enables the oxidation of proteins, which are an integral part of the structure of most microorganisms such as bacteria, fungi, yeasts and viruses. For industrial use NaOCl can be blended with surfactants to provide prolonged contact times when using it as foam or to improve the wetting properties.

NaOCl is very effective even at low concentrations on clean surfaces. When using NaOCl-containing biocides, care should be taken that the previous cleaning was successful. As with many disinfectants, microbiological efficacy is influenced by organic dirt residues.

Due to the high oxidation potential, the resistance of materials of construction must be considered. The manufacturers of biocides based on NaOCl can reduce harmful influences on materials by adding inhibitors or by adjusting the pH to 9-10. Particular attention must be paid to the risk of pitting corrosion (table 7). NaOClbased biocides should not be left on food contact surfaces and should be rinsed off after its recommended contact time. Advantages and disadvantage of NaOCl are listed in table 8.

*DIN 11 483 Part 1: "Dairy plants; Cleaning and disinfection; Consideration of the influences on stainless steel "

Advantages Disadvantages

Wide activity spectrum

Effective at low concentrations

Resistant to hard water

Efficiency at low temperature

Easy to analyse (concentration used and remaining after rinsing)

Could be used for foam free disinfection

Can be blended with surfactants for foam application or to improve wetting

Other Chlorine Donors

Reduced effectiveness in the presence of organic matter

Corrosion risk to some materials, e.g., pitting

Toxic by-products (AOX, Chlorate, Chlorite)

Irritation, toxic gas formation when mixed with acids

Short shelf life of only (~ 6 months for undiluted solutions; the shelf life for diluted solutions is much lower).

Another way to achieve disinfection using chlorine is in concentrated tablet form. Typically, these tablets consist of di-chloroisocyanurate (DCC), a chlorine donor, giving approx. 33% available chlorine. Tablets provide a safe and reliable method of making up an effective working solution for small applications.

Chlorine Dioxide (ClO2)

It is a relatively small, volatile, and highly energetic molecule, and a free radical even while in dilute aqueous solutions. It disinfects by oxidation; however, it does not chlorinate. ClO2 is mainly used for the disinfection of water systems but can be applied to food contact surfaces by using one of several different blends of chemicals (specialised dosing system):

• Chlorine with chlorite.

• Acid with hypochlorite and chlorite.

• Acid with chlorite.

• Stabilised form of ClO2 with a low pH acid activator.

• Peroxydisulfate with chlorite.

Used as a gas for room disinfection a typical chlorine dioxide decontamination cycle at ambient temperature(25–30°C) consists of three phases in a one-step process:

• Humidification to 70–90%

• Decontamination, where the gas is generated in situ from dry sodium chlorite and chlorine gas in a nitrogen carrier, and is injected into the room at a concentration between 0.5–30 mg/L

Table 7 - Recommended max. concentrations of NaOCl media and contact times considering the risk of pitting corrosion on stainless steel (AISI 316: 1.4401/1.4436; AISI 304: 1.4301; AISI 316Ti: 1.4571)*

Table 8 – Advantage and Disadvantages of NaOCl

• Aeration by neutralisation of the gas with sodium bisulphite to a concentration below 0.1ppm.

Hydrogen Peroxide (H2O2)

H2O2 works in the same manner as NaOCl but may not be as effective against as many micro-organisms. It is low foaming and ideal for CIP systems. Used at elevated temperatures, H2O2 becomes more effective. Efficacy also depends strongly on the pH: effective in alkaline conditions, while highly stable under acidic conditions. At higher concentration it is used for aseptic processes.

Vaporised hydrogen peroxide can be used as a low-temperature anti-microbial vapour to decontaminate sealed and closed manufacturing areas. VHP is produced from a solution of liquid hydrogen peroxide and water, by generators specifically designed for the purpose. These generators initially dehumidify the ambient air, then produce VHP by passing aqueous hydrogen peroxide over a vaporiser and circulate the vapour at a programmed concentration in the air, typically from 140 ppm to 1400 ppm depending on the infectious agent to be cleared.

After the VHP has circulated in the enclosed space for a pre-defined period of time, it is circulated back through the generator, where it is broken down into water and oxygen by a catalytic converter, until concentrations of VHP fall to safe levels (typically <1 ppm). Alternatively, the VHP is vented to the outside air, in cases where recapturing of the VHP is not needed.

Hydrogen peroxide may attack aluminium, zinc, tin, or their alloys.

Peracetic Acid, PAA (CH3CO3H)

Peracetic acid (PAA) is also known as peroxyacetic acid (POAA). Peracetic acid (PAA) is an excellent antimicrobial agent that is very effective against a variety of microorganisms and can be used for various disinfection applications. It can be used for closed systems as well as for open surfaces in the food and beverage industry.

PAA is a low-residue biocide with a very broad spectrum of activity. The use of PAA to disinfect surfaces and circuits within the food industry is widespread. The degradation products created during disinfection are harmless (acetic acid, oxygen and water), which minimises risks to the environment and human health when PAA is used.

The United States Environmental Protection Agency (EPA) describes peracetic acid as an ideal antimicrobial agent due to its high oxidation potential on the outer membrane of bacteria, endospores, fungi, viruses and yeasts. The oxidation mechanism of PAA is based on the transfer of electrons from the oxidised form of the acid to the microorganisms, thereby killing or inactivating them. PAA even remains effective at low temperatures.

High biocide capacity and the broad spectrum of activity tolerate the presence of organic residues significantly better than other oxidative media such as NaOCl or Electrochemical activated water (ECA-water, see Appendix 4).

With suitable surfactants, the wetting behaviour can be improved, and foaming disinfectants can be formulated. Acid is added in some PAA-containing disinfectants, so that it is possible to carry out phase separations in CIP systems using conductivity.

Due to these characteristics and benefits, PAA-based disinfectants are used in a wide variety of industries such as meat processing, canning and dairy operations, beverage industries, as well as fresh and/or frozen vegetable, meat, fish industries. In many areas, PAA is the first choice of disinfectant in closed systems. It is used to disinfect CIPs, pasteurizers, tanks, surfaces, or fillers. It can also be used in carbon dioxide environments, for example in fermentation tanks, aging tanks or carbonators, among others in the beer, wine and bottling industries.

The latest generation of peracids also contain peroctanoic acid in addition to PAA. Due to the lipophilic properties of peroctanoic acid, the phospholipid layers of the microorganisms can be penetrated considerably faster. This significantly increases the microbiocidal performance. As a result, application concentrations can be reduced and application times shortened, which protects the production systems and makes the disinfection process even safer and more economical.

Advantages and disadvantages of Peracetic Acid are listed in table 9.

Advantages

Wide activity spectrum

Wide temperature range of activity

No formation of critical by-products

Easy to analyse (application and remaining)

Easy to rinse off

Tolerates organic dirt better than chlorine

Toxicologically and ecologically safe

Applicable for CIP

Can be blended with surfactants for foam application or to improve wetting

Iodophors

Disadvantages

Smell of the concentrate and in open applications

Corrosive to some materials

Not suitable for manual disinfection, e.g., wiping

Low wetting properties

Requires separate storage per Globally Harmonized System (GHS)

Iodophors are expensive but very effective disinfectants having both detergent and disinfectant properties. They are produced by dissolving iodine in an acid medium together with surfactants. Iodophors have several advantages including:

• The ability to kill a wide range of organisms at low temperatures.

• Short contact time.

• The ability to cope with soiling/hard water.

However, even at the correct concentration they can cause taint if left on a surface without rinsing. They may also turn some plastics brown and should not be used on soft metals. Iodophors are very effective in dirty applications such as drive-over disinfectant mats.

Ozone

Ozone (O3) is an oxidizing agent with a slight but characteristic odour. It provides rapid antimicrobial activity and is effective against a broad spectrum of microorganisms, though less effective against spores. Ozone oxidises organic material within bacterial membranes, weakening the cell wall and leading to cell rupture, with immediate death of the cell as result.

Ozone spontaneously decomposes rapidly to oxygen (half-life at ambient temperatures is about 10-20 min).

O3 applied as a gas successfully penetrates into many geometric shapes, with the potential to decontaminate product contact surfaces, as well as air handling systems and process areas. However, experiments have shown that the efficacy of O3 decreases with increasing loads of adsorptive and proteinaceous soil. Also, higher room humidity is required to obtain increased antimicrobial activity, especially because dormant microbial cells in a dry environment are extremely resistant to gaseous O3. Gaseous O3 loses bactericidal effect at ≤ 50% RH, requiring an increase in humidity (RH, 70-80%) in the area before starting the disinfection process [25]

Due to its reactive, unstable nature, ozone must be produced at the point of use. This is done on-site by ultraviolet irradiation of air or by passing a high-voltage discharge through air. Ozone generators effectively pass air through the high-energy source within the equipment and the resulting physicochemical reaction leads to the formation of ozone gas that can be used to decontaminate the area or surface. It is relatively expensive and specialized equipment. It should be realised that ozone is able to oxidise some types of materials such as neoprene, nylon, Buna N, natural rubber, some plastics (LDPE and polyoxymethylene), silicone grease and

Table 9 – Advantage and Disadvantages of Peracetic Acid

even some metals. It must not be used in an area where operators are present because of health and safety concerns [21],[26]

A typical ozone decontamination cycle consists of three phases in a one step process:

1. Humidification: for maximum antimicrobial activity of ozone, the area being decontaminated needs to be humidified to 70 to 80%.

2. Decontamination: the ozone initially reacts with any volatile organic compounds present in the atmosphere of the area being decontaminated, a process known as ozone debt absorption. Once overcome, the ozone concentration builds rapidly to a concentration between 8–25 ppm, and the ozone generator maintains the optimum biocidal level by adapting to changing environmental conditions for the minimum time needed for maximum kill.

3. Aeration: the ozonised room space must be fully ventilated before factory operatives are able to reenter. Some ozone generation companies have developed systems to chemically ‘quench’ the ozone rather than waiting for levels to reduce naturally. It destroys the remaining ozone leaving the room clean, safe and fresh for immediate re-occupation (OSHA permissible exposure limit: 8-hour time weighted average 0.1 ppm, immediately dangerous to human life or health at 5 ppm).

Cycle times vary depending on the area volume, desired level of decontamination and area contents, but are typically between 2-4 hours.

Non-Oxidising Disinfectants

Alcohols

Where there is a requirement for cleaning and disinfection in an essentially ‘dry’ area, such as a bakery, then the use of an alcohol-based spray/wipe product becomes very useful. This is typically a blend of alcohol (3080%) and surfactant to provide good disinfection in lightly soiled conditions therefore reducing the amount of water used. The alcohol evaporates quickly after application, making undesirable wipe-dry operations unnecessary. Care must be taken because of the flammability of the commonly used alcohols such as ethanol and propanol. Alcohol disinfectants have also been adapted for use as post wash hand disinfectant.

Amphoterics

Amphoterics are excellent disinfectants that also can be impregnated into wipes, but they can be expensive. They have low toxicity, are relatively non-corrosive, tasteless, odourless and are used at approximately 1% v/v. Amphoterics are formulated from surfactants and therefore they are high foaming and unsuitable for use with machines and high velocity sprays (e.g., CIP). Formulations often have similar co-formulants to QAC based products, and the same sets of efficacy and taint tests are usually required.

Water chemistry can have a major influence on their biocidal properties, and they are not as robust as triamine derived products (9.2.3.3). At low pH (below ~ pH4) they are cationic and excellent biocides. If the pH is increased, their biocidal performance is reduced.

Triamines

Triamine based disinfectants are often confused with amphoteric disinfectants (9.2.3.2). They are quite different in their chemical structure and their biocidal activity is associated with two primary amine (NH2) groups.

At a high pH they are uncharged, but when the pH reduces, they become positively charged, resembling QAC based disinfectants. Both amine types (uncharged and charged) have excellent biocidal properties. They are excellent disinfectants that can also be impregnated into wipes; however, they can become more expensive as compared to QAC based disinfectants (9.2.3.4). Triamines are also like amphoterics, being relatively noncorrosive, tasteless and odourless when used in accordance with manufacturer’s instructions at concentrations, typically at 1% v/v. As with amphoteric disinfectants, triamines are also high foaming.

Quaternary Ammonium Compounds, QAC’s

QAC’s (or QUAT’s) are effective against gram positive bacteria and yeast but less effective against gram negative bacteria, spores, and moulds. In a properly formulated spray/wipe product this obstacle can be overcome. QAC based disinfectants are stable and generally taint free. They may be inactivated by hard water, organic material and some plastics. To improve the effectiveness of QACs, formulations often include sequestrants and non-ionic detergents. QAC’s should not be used for CIP application due to their foaming behaviour.

Didecyldimethylammonium-chloride (DDAC) and benzalkonium chloride (BAC) are quaternary ammonium compounds that deliver a biocidal effect against microorganisms. These substances are commonly formulated into disinfectants used in the food Industry for hard surface disinfection, both for food contact and non-food contact surfaces, and also may be used in other applications throughout the food chain. In Europe, as of 12th

November 2014, specific maximum residue limits (MRLs) for DDAC and BAC in food and feed are set at 0.1 mg/kg for all food commodities as defined by regulation (EC) No. 1119/2014 amending Annex III of regulation (EC) No. 396/2005. For baby food manufacturers the max. residual limit in the EU is 0.01 mg/kg of product. Recently, concerns regarding the use of QAC’s were raised in Europe, as their use may support the formation of antibiotic resistance (Swiss Expert Committee for Biosafety, EFBS).

Effectiveness of Chemical Disinfectants

Unlike antibiotics, disinfectants do not act according to the key-keyhole principle, in which the active ingredient attacks the metabolism of the cells at very specific locations. The mechanism of action of disinfectants is nonspecific, determined by many factors and uncompromising.

Disinfectants can act on microorganisms in different ways, such as action on the bacterial cell wall, the nucleus, the metabolism, or the DNA. Typically, mode of actions depends on the type of organism and includes destruction of enzymes and proteins within the cell or cell membrane. Among others, the following mechanisms are responsible for irreversible damage to the cells:

• Inactivation of cellular respiration or catabolic and anabolic reactions.

• Disruption of replication.

• Loss of membrane integrity with the leakage of essential intercellular components, such as potassium ions, inorganic phosphates, pentoses, nucleosides, and proteins.

• Destruction of the cell membrane, dissolution of cells (lysis).

• Damage to the transmembrane proton movement leads to the disturbance of the oxidative phosphorolysis and inactivation of the active transport through the membrane. The regulation of biological processes in the cell is irreversibly impaired.

• Coagulation of intercellular material.

Studies have shown that here is a descending order of microbial tolerance to disinfectants [44]:

• Spores

• small non-enveloped viruses

• gram-negative bacteria

• Fungi

• large non-enveloped viruses

• gram-positive bacteria

• enveloped viruses

With respect to the effective use of disinfectants, the information provided by the manufacturer such as concentration, contact time and temperature (all based on recognised microbiocidal standard tests), should be followed.

Disinfectants for food processing plants are used at concentrations far above the inhibitory effect. Thus, the microorganisms are destroyed to a microbially acceptable level as long as the surface has been sufficiently cleaned first, is sufficiently drained of rinse water and that the manufacturer’s instructions have been followed. Compliance with the recommended exposure times of the disinfectant solution at completely wetted surfaces is important.

The performance of a number of common food industry disinfectants, at a recommended contact time of 5 minutes, is compared and contrasted in table 10 below.

Disinfectant Type Typical Use Concentration

Chlorine Compounds 50 – 1000 ppm Av. Cl.

Hydrogen Peroxide 100 – 1000 ppm

Peracetic Acid

Iodophors

QAC

50 – 200 ppm

10 -100 ppm

200-1000 ppm

Amphoterics 1000ppm

Triamines 1000ppm

Alcohol 60 -70%

Physical Disinfection

Steam, hot water

Thermal disinfection is a method of disinfection which relies on heat to kill bacteria and viruses by exposure to a specific temperature for a set amount of time and can be applied to disinfect food processing surfaces. The high-temperature disinfection process can destroy the proteins in viruses and bacteria by coagulation and rendering the microorganisms as dead or inert.

Hot water or steam can be used for disinfection of equipment. Using hot water is an excellent method of destroying microorganisms. However, it is mainly used within enclosed machines such as tray and dish washers and not for open plant disinfection due to the risk to personnel. Plastics are good heat insulators and often short treatment times do not provide microbiological safety.

Thermal disinfection is only effective if all contact surfaces are subjected to the required temperature and time combination.

Steam, using steam jets can be used within food factories for disinfecting equipment, and is typically performed on a small scale. One advantage of steam is that surfaces are self-drying. However, it can have an adverse effect on certain materials e.g., some plastics and the removal of food grade lubricants from equipment. Also, condensation on adjacent colder surfaces can be an issue in areas with poor air extraction.

Moist heat is more efficient than dry heat for inactivation of microorganisms. For circulating systems moist heat in the form of hot water can be used for disinfection. Where heat disinfection is used, the process must be regularly monitored using a robust preventive maintenance programme to ensure that the correct parameters of temperature and time are being met.

The basis of thermal disinfection (other than in aseptic processing) is to provide a pasteurisation treatment, defined as a 6-log reduction of vegetative food pathogens. This is typically seen as a 70°C for 2 minutes process. There is a relationship between process temperatures and times for most food pathogens, and as a conservative estimate, for every 7°C rise or fall in temperature, there is a 10-fold reduction or increase in contact time respectively. So, the following temperatures and times are the equivalent to a 70°C 2 minutes process:

• 63°C for 20 min (1200 seconds)

• 70°C for 2 min (120 seconds)

• 77°C for (12 seconds)

• 84°C for (1.2 seconds)

Table 10 –Typical disinfectant types used in the food industry; actual concentrations depend on application (per advice by the chemical supplier) and local regulations

All the above times/temperatures are theoretical and only apply when the temperature for all the equipment surfaces has approached the target temperature. In practical terms, longer times should be applied (e.g., 85°C/1 minute).

Thermal disinfection has an excellent bactericidal and fungicidal effect, except for very heat resistant moulds. However, it has no effect on bacterial spores under open plant conditions.

Thermal disinfection does not leave any chemical residues and no additional rinsing with water is required. Since heat is used for disinfection, the equipment may need to be cooled prior to the start of production, which can require additional time. Thermal disinfection has a very good penetration effect and is not as sensitive to the presence of organic matter as a chemical disinfectant. Thermal disinfection is not corrosive to the equipment, as long as the quality of the water is within the specifications (see 6.3). The energy consumption required for thermal disinfection can be quite significant, when compared to chemical disinfection, which can negatively impact the environmental performance of the manufacturing site.

Dry heat

This involves disinfection of surfaces using dry air at a high temperature and as the name suggests, it involves no use of steam or water. Dry heat destroys microorganisms by oxidation of the cell proteins and other components present within the microorganisms. For example, items of equipment or dismantled parts are placed into a hot air oven.

Dry heat disinfection takes more time than moist heat disinfection. For example, a study using dry heat to thermally inactivate Listeria innocua on deli slicer components found out that dry thermal treatment at 80°C and times up to 15 h were not sufficient to achieve a 5-log reduction of residual Listeria innocua having survived improper cleaning and disinfection of the deli slicer. However, a three-hour treatment at 80°C gave a 2 or 3 log reduction, which would likely be adequate for a machine that had been cleaned and disinfected prior to heating. Dry thermal heating overnight could be a suitable decontamination method to reduce microorganisms to an acceptable level in the worst-case scenario of an inadequately cleaned and disinfected slicer [16].

Some strains of Salmonella spp. are super resistant to dry heat [36] as shown in table 11:

* all organisms have a 6-log reduction – i.e.,

UV-C Radiation

Ultraviolet (UV) rays are part of the natural sunlight and are known for its antimicrobial effect. UV rays with wavelengths between 200 and 280 nanometres (nm), known as UV-C light, have a maximal germicidal effect on bacteria, viruses, yeasts, moulds, and algae at a wavelength of 253.7 nanometres (nm). Maximum absorption of UV-light by DNA occurs at this wavelength. At shorter wavelengths (e.g.,185 nm), UV-C light also generates ozone, hydroxyl and other free radicals that also contribute to the germicidal effect.

Typical applications for disinfection in the food manufacturing industry include (figures 18-21):

• Air decontamination (Air Handling Units, AHU)

• Surface decontamination (for example conveyor belts, tables, etc.)

• Decontamination of packaging material just before packing

• Water treatment (potable water, wastewater)

Table 11 – Resistance of Salmonella spp. in liquid to dry heat*

UV-C light damages the cellular DNA of a microorganism and its replication will be inhibited, if microorganisms are exposed at the lethal dose needed (table 12). The dose (expressed as mJ/cm² or mW.s/cm²) is the mathematical product of intensity (mW/cm2) of the source and the time in seconds (s) the microorganism is exposed to the source. The lethal dose needed to ensure a microbial cell loses its reproductive capability, is inactivated and will not self-repair varies depending upon the type of microorganism.

kill

Microorganism

Algae 300-600

To increase the efficacy to 99% (2-log reduction) the dose must be doubled. To increase the efficacy up to 99.9% (3-log reduction), it needs to be tripled. The lethal dose required to obtain the expected log reduction rate of the targeted microorganisms is an important parameter in the design and selection of suitable UV-C radiation sources.

UV-C rays are usually produced with low-pressure mercury vapor arc lamps (low electrical power from 3 to 175 W) or by medium pressure arc tubes (electrical power from 0.5 to 5 kW). To avoid foreign body contamination risks the lamps should have a protective sleeve or be covered with a film, transparent for UV-C rays.

Figure 19 - Unit with 4 low-pressure mercury vapour lamps for room and surface treatment (courtesy of ERIES)

Figure 18 - Decontamination of pots before the filling step (courtesy of ERIES)

Figure 20 - UV-C treatment of a conveyor belt (courtesy of ERIES)

Figure 21 - UV-C application in an air-duct (courtesy of ERIES)

Table 12 - lethal dose (in mJ/cm²) necessary to

90% (1-log reduction) of the respective microorganisms

The intensity of lamps decreases over time. To ensure that their effectiveness does not drop below an acceptable level the time of use needs to be monitored and included in the facility’s preventive maintenance program along with the equipment necessary for the proper operation of the UV-C device. Typically, a lamp’s life is 9000 h of running (some models achieve 16000 h). They should be replaced as per the manufacturer’s advice at the end of their life.

Human eyes and skin may be injured if exposed to UV-C rays. Suitable personnel protection equipment (PPE), such as gloves, arm sleeves, and protective sunglasses or clear plastic face shields should be worn by operators in the proximity of the UV-C source.

UV-C rays effectively reduce the level of microbial contamination on clean surfaces or in media (air, water), if it can strike unprotected cells. Shadowing effects caused by the topography of surfaces or the geometry of the design (spots that cannot be reached by the UV-C light) lower the disinfection efficacy significantly. Notice that UV-C light may not pass through certain fluids and transparent materials. A transparent acrylic glass panel for example is transparent to visible light, but impervious to UV-C rays. The turbidity in fluids may significantly reduce the penetration depth and prohibit that the sufficient dose is delivered. In water applications, algae formation or scale deposits on lamp housings can also reduce the efficacy.

Ionisation

Air, that naturally contains moisture, is passed over ionising tubes emitting a high voltage discharge, such as a corona, to produce positively and negatively charged ions (e.g., super oxide anions O2●-), as well as radicals (e.g., hydroxyl radicals OH●). These reactive species interact with the naturally charged airborne microorganisms in the air to inactivate and remove them.

Some commercial units combine non-thermal plasma and UV catalysis to deliver a continuous supply of hydroxyl radicals destroying microorganisms both in the air and on surface contact. The hydroxyl radicals that come into contact with contaminated surfaces can kill the bacteria within hours. This technology can be adapted to specific environments and applied as portable stand-alone units or incorporated into HVAC systems.

Vapours and gases have several advantages as they can effectively penetrate every part of a room, including sites that are difficult to access with conventional liquids or to manual disinfect.

Selection of Disinfectants/Methods of Disinfection

In the selection and application of disinfectants site-specific conditions should be considered. Disinfection procedures should be used according to the specific requirements, for example, after a batch, after a defined production run time daily, weekly or during special occasions. Efficacy testing results help to identify the most appropriate biocide. An overview of advantages and disadvantages of selected disinfectants and methods of disinfection is shown in Appendix 6.

The following factors should be taken into account when choosing a method of disinfection:

• Microorganisms to be destroyed (effectiveness)

• Impact of soil residue left on surfaces

• Contact time and concentration

• Type of surfaces to be disinfected

• Material compatibility

• Sensitivity of the food production process

• Risk of food adulteration (e.g., taint issues)

• Toxicity of disinfectant, and effect on personnel

• Safety for personnel

• Environment, including effluents and effluent treatment

• Method of application (liquid, spray, aerosol; label requirements, etc).

• Application temperature range

• Stability, shelf life and its impact on dilution ratio’s

• Water quality (hardness, chlorine level, etc.)

• Cost Effectiveness

Modes of Application

Circulation (CIP)

Disinfection solutions are circulated in closed systems after thorough cleaning. Usually, as the penultimate stage in a CIP-sequence before the final rinse with potable water and at ambient temperature. Further information on CIP-installations is detailed in EHEDG document N° 50. Use concentrations are typically 0.5-1% w/w, depending on the formulation. Non-foaming formulations (without detergents) are preferred in order to achieve thorough

wetting of all surfaces. For the same reason, disinfectants with active ingredients that have inherent foaming tendencies (e.g., QAC) are not recommended in CIP-applications.

Spray Disinfection

Spray disinfection is the most common method for applying disinfectant to surfaces. It is versatile, provides good coverage and is an economic means of applying disinfectant solution.

It can be carried out by using a variety of different applicators (figure 22). The most common are

• Small, hand-held trigger sprayers,

• Pump-up sprayers incorporated into a rucksack type design.

• Compressed air driven sprayers

• Via a medium-pressure system, such as a System Cleaners Unit (mobile or static).

Soak Disinfection

This is probably the most effective means of disinfection as the item to be disinfected is fully immersed in the disinfectant solution, providing an excellent contact time to all surfaces. It is important that items are effectively rinsed before disinfecting as detergent residues or debris deactivate the disinfectant.

Ideally soak disinfection should be separated from the rinsing and detergent cleaning steps and a 3-compartent sink (typically, the third compartment is used for disinfection) should be effectively controlled to avoid crosscontamination.

This type of disinfection method is usually confined to small items such as utensils, knives, blades, small machinery parts, cutting boards, etc.

The disinfectant solution in the sink can be made up by using a wall-mounted plunger dosing unit or a proportioning unit.

Foam Disinfection

The foam disinfect is usually a surfactant-based biocide applied with the same equipment used for foam cleaning. The use concentration is typically 0.5 - 1 % w/w (1-2 % v/v) depending on the used formulation. Air is brought into the solution.

The foam application allows better visibility of the product, allowing the operator to see the surfaces which have been covered

Fogging

Fogging is done by using

• a static, purpose-built system, in an area of a factory, with strategically placed nozzles in production areas larger than 300m³.

• various types of mobile units appropriate for rooms up to 300 m³ (figure 23).

Figure 22 - various types of sprayers: backpack Sprayer; low-pressure system; dispenser (courtesy of Halag Chemie and Holchem)

The systems work by supersaturating the atmosphere with a fog of disinfectant chemical. The area that can be covered varies depending on the application system.

The fogging takes approx. 30-45 minutes to complete, followed by a settling period of about 45-60 minutes. Personnel should only enter the fogged area after thorough aeration. It might be required to protect sensitive equipment (e.g., checkweighers, metal detectors, printers etc.).

Fogging is only effective if sufficient chemical is deposited onto all food contact and other surfaces in the environment. This is a function of both the volume of disinfectant fogged (the larger the volume, the better the disinfection) and the particle size of the fogged particles. Particles of > 25 µm quickly fall to the floor or exposed horizontal surfaces at a lower level of the room, whilst particles <10 µm may remain suspended in the air for considerable lengths of time. Particles within this range, circulated with an air velocity at the nozzle of 100 m/s, remain airborne long enough to settle on surfaces. However, there is little or no contact with underside surfaces. Larger particle sizes can be used if the air velocity is increased or fans are used to assist the distribution of the droplets.

Research has suggested that fogging with a suitable disinfectant is effective in reducing airborne microbial populations by 2-3 log orders in 30-60 minutes. A 6-log reduction can be achieved on horizontal surfaces in 60 minutes, but the effect is minimal on vertical surfaces. There is also little or no effect underneath equipment.

To ensure that fogging has been successful and has reached the hardest to access air spaces, it is good practice to locate disinfectant test strips (e.g., QAC test paper for quaternary ammonium compound-based disinfectants, PAA test strips for peracetic acid-based disinfectants or non-pathogenic microorganism strips) in these areas.

Due to the non-uniform disinfection effect of fogging, it should never be used as alternative to surface disinfection. Fogging should only be conducted, if cleaning and disinfection of all food contact surfaces has taken place.

Whole Room Disinfection

End of production cleaning and disinfection is selective to food contact surfaces, but microorganisms may survive in the wider environment, particularly in hard-to-reach areas and surfaces at higher level within the food processing facility.

Whole room disinfection allows the entire environment to become saturated with a specific chemical disinfectant in order to achieve disinfection of all areas – food, non-food and those harder to reach areas.

This technique can be used on a routine basis or as part of periodic cleaning and disinfection procedures, or it may only be used for decontaminating an area after a pathogen contamination incident.

The degree of disinfection a whole room disinfection system can achieve should be considered. Some systems achieve partial decontamination of all exposed room surfaces, such as exposed vertical and horizontal surfaces; some may achieve complete decontamination (food processing equipment, ceilings, walls and floors), while others may also include some penetration into equipment to contact indirectly exposed surfaces. They may also provide disinfection of the air in the area being treated.

The range of techniques include:

• Chemical fogging (typically PAA, QAC, Amphoteric)

• Vaporised hydrogen peroxide

• Ozone

• Chlorine dioxide

Figure 23 - fogging device (courtesy of Halag Chemie)

• Ultraviolet light

• Ionisation.

Cleaning Programmes

A plant specific cleaning programme must ensure that GMP conditions and local regulatory requirements in the food manufacturing environment will be met. It comprises effective and efficient cleaning of the equipment as well as all manufacturing areas of the site. A written programme should include

• GMP rules for the staff conducting the cleaning and disinfection.

• Requirements for managing cleaning tools, to prevent cross-contamination.

• Cleaning protocols detailing what, how and when equipment and areas are to be cleaned

• Validation, Monitoring and Verification activities.

• Training for personnel involved in the cleaning and disinfection to develop skills and capabilities.

Typically, the accountability for the development and supervision of such a programme is with the Quality department. The related tasks of the Quality department include writing effective and efficient cleaning procedures, providing cleaning schedules, training of the personnel (internal or external) conducting the cleaning and self-inspections, and undertaking validation, monitoring and verification activities.

Good Manufacturing Practices (GMPs)

All personnel involved in cleaning and disinfection activities should comply with the same facility specific GMP requirements laid down for food manufacturing. These requirements should be written in documents available to all personnel at all times. General GMP requirements should consider and address:

• Personnel practices and prohibited acts

• Clothing and personal equipment

• Hand wash and disinfection

Incremental GMP requirements as regards cleaning and disinfection should be developed and communicated, and may include for example:

• Hygienic use of spray devices to avoid that water/solutions splash from the floor or from unclean surfaces onto cleaned surfaces.

• Measures required to prevent cross-contamination during cleaning activities at lines in close proximity to other lines with exposed product/product contact areas.

• Preventing water/cleaning solutions from flowing from areas where cleaning is conducted into areas where product is being produced.

• Preventing placing dismantled equipment on the floor to be cleaned.

• Preventing floor-based items, e.g., drain parts, being placed on food contact surfaces for cleaning

• Preventing cleaning equipment in contact with the floor, e.g., hoses, passing over food contact surfaces

Cleaning Tools

Tools (utensils and equipment) used during cleaning and disinfection operations should be hygienically designed and used in a manner so as to prevent biological (e.g., microbial, insects), chemical (e.g., allergens, cleaning and disinfection chemicals) and physical (e.g., foreign bodies) contamination risks. This includes materials of construction which should be compatible with the cleaning regime, and a tool design that does not allow for any harbourage areas.

Tools used for product contact should be segregated from tools for non-product contact areas, as well as areas with different microbial or allergen risk profiles defined as per the zoning assessments. Clear identification of all reusable tools can be done by colour coding. To manage contamination risks, colour coding can be applied to dedicate tools to separate

• product contact surfaces

• external surfaces of equipment that are close to the floor

• floors

• drains

• general production environment (e.g., ceilings, walls)

• allergen containing surfaces and zones

• toilets/rest rooms

After use, tools should be cleaned and disinfected (if necessary) and stored in dedicated areas as per their colour code scheme. Wet cleaned tools should be stored in a way as to allow for draining and drying. Before each use, cleaning tools should be routinely inspected for damage and replaced as necessary.

Standard Operating Procedures (SOPs)

For conducting effective and efficient cleans, the application of validated cleaning and disinfection procedures is key. SOPs are procedures detailing what to clean, how to clean, how often to clean, and the records used for verification and monitoring. They may refer to parts of equipment or an entire production line/process. SOPs may also be used as the basis when developing training materials.

Clear, relatively simple language in an easy-to-read format should be used. Any ambiguity and long instructions should be avoided. Including pictures or sketches is very powerful for illustration. Notes for clarification should be included only, if needed (e.g., for identifying specific hazards)

As SOPs should be available on-site when the cleaning is undertaken, copies of the documents needed for cleaning should met GMP requirements (e.g., water-proof documents).

An SOP for cleaning and disinfection should contain:

• Title of the document (name of the procedure) with version number, document reference number and effective date

• Page numbers

• Objective & Scope (equipment to be cleaned and its location)

• Responsibilities for dismantling, cleaning, and inspection

• Personal Protection precautions (protective workwear, such as for example rubber suits, rubber boots, gloves, goggles)

• Instructions for disassembling/re-assembling

• Frequencies of the cleaning tasks (routine cleaning, deep cleaning, periodic cleaning)

• Numbered sequence for the completely described cleaning and disinfection steps

• Relevant parameter values: chemicals to be used (type, brand, name, concentration), temperature and time conditions for each step

• Tools and utensils to be used for cleaning and disassembling

• Particular monitoring and verification activities (for example: visual inspections post-cleaning, ATP measurements, etc.)

• Key inspection points (photos are recommended)

• Corrective and Preventative Action (CAPA) requirements in case of deviations.

• Record keeping requirements.

• Referenced documents and checklists (e.g., monitoring and verification)

• Revision log with signature & date lines for the SOP content and updates

A template for a SOP is available for free downloaded [45].

Validation - Monitoring - Verification

Validation, monitoring and verification should not be understood as programmes and activities in isolation, but rather as one concept with different activities occurring during different stages in a food manufacturing environment, with the objective to demonstrate that a cleaning regime shows effective and consistent results. Though the terms are often used interchangeably, the three activities have very different meanings. General definitions of validation, monitoring and verification are provided with the Codex Alimentarius and the EHEDG glossary.

In brief the 3 activities comprise:

• Validation: Is the cleaning regime as described effective?

• Monitoring: Is the SOP adhered to?

• Verification: Was the SOP adhered to?

EHEDG document N° 45 gives in detail recommendations on how to implement cleaning validation, monitoring, and verification protocols.

Training

For each food manufacturing facility, a tailored training program should exist to ensure that the personnel (including contracted cleaning companies) undertaking the cleaning of the equipment, as well as the validation, monitoring and verification activities have the correct level of skills and competence.

Competency should be assessed after the training, and refresher training should be undertaken as required.

Supplementary Reading

[1] Alvarez, N., Daufin, G. & Gésan-Guiziou, G. (2010). Recommendations for rationalizing cleaning-in-place in the dairy industry: Case study of an ultra-high temperature heat exchanger. Journal of Dairy Science, 93 (2), 808821.

[2] Axelsson, L., Holck, A., Rud, I., Samah, D., Tierce, P., Favre, M. & Kure, C.F. (2013). Cleaning of conveyor belt materials using ultrasound in a thin layer of water. J. Food Protection, 76 (8), 1401-1407.

[3] Augustin, W. & Bohnet, M. (2001). Influence of a pulsating flow on fouling behavior of heat transfer surfaces. Chemie Ingenieur Technik, 73 (9), 1139–1144.

[4] Bénézech, T. & Faille, C. (2018) Two-phase kinetics of biofilm removal during CIP. Respective roles of mechanical and chemical effects on the detachment of single cells vs cell clusters from a Pseudomonas fluorescens biofilm. Journal of Food Engineering, 219, 121-128.

[5] Blel, W., Bénézech, T., Legentilhomme, P., Legrand, J. & Le Gentil-Lelièvre, C. (2007). Effect of flow arrangement on the removal of Bacillus spores from stainless steel equipment surfaces during a cleaning in place procedure. Chemical Engineering Science, 62 (14), 3798-3808.

[6] Blel, W., Legentilhomme, P., Bénézech, T. & Fayolle, F. (2013). Cleanability study of a scraped surface heat exchanger. Food and Bioproducts Processing, 91 (2), 95-102.

[7] Blel, W., Mehdi, D. & Sire, O. (2015). Effect of a new regeneration process by adsorption-coagulation and flocculation on the physicochemical properties and the detergent efficiency of regenerated cleaning solutions. Journal of Environmental Management, 155, 1-10.

[8] Boyce, A., Piterina, A.V. & Walsh, G. (2010). Assessment of the potential suitability of selected commercially available enzymes for cleaning-in-place (CIP) in the dairy industry. Biofouling, 26 (7), 837-850.

[9] CEN (2013 +A2:2019). EN 14476 Chemical disinfectants and antiseptics. Quantitative suspension test for the evaluation of virucidal activity in the medical area. Test method and requirements (Phase 2/Step 1), European Committee for Standardization, Brussels, Belgium, 43 p.

[10] CEN (2015). EN 13697 Chemical disinfectants and antiseptics - Quantitative non-porous surface test for the evaluation of bactericidal and/or fungicidal activity of chemical disinfectants used in food, industrial, domestic and institutional areas - Test method and requirements without mechanical action (phase 2, step 2), European Committee for Standardization, Brussels, Belgium, 42 p.

[11] CEN (2018). EN 13704 Chemical disinfectants - Quantitative suspension test for the evaluation of sporicidal activity of chemical disinfectants used in food, industrial, domestic and institutional areas - Test method and requirements (phase 2, step 1), European Committee for Standardization, Brussels, Belgium, 44 p.

[12] CEN (2019a). EN 1276 - Chemical disinfectants and antiseptics - Quantitative suspension test for the evaluation of bactericidal activity of chemical disinfectants and antiseptics used in food, industrial, domestic and institutional areas - Test method and requirements (phase 2, step 1), European Committee for Standardization, Brussels, Belgium, 44 p.

[13] CEN (2019b). EN 1650 - Chemical disinfectants and antiseptics - Quantitative suspension test for the evaluation of fungicidal or yeasticidal activity of chemical disinfectants and antiseptics used in food, industrial, domestic and institutional areas - Test method and requirements (phase 2, step 1), European Committee for Standardization, Brussels, Belgium, 44 p.

[14] Chee, M.W.L., Ahuja, T.V., Bhagat, R.K., Taesopapong, N., Wan, S.A., Wigmore, R.L. & Wilson, D.I. (2019). Impinging jet cleaning of tank walls: Effect of jet length, wall curvature and related phenomena. Food and Bioproducts Processing, 113, 142–153.

[15] Christensen, B.E., Trønnes, H.N., Vollan, K., Smidsrød, O. & Bakke, R. (1990). Biofilm removal by low concentrations of hydrogen peroxide. Biofouling, 2 (2),165-175.

[16] Crandall, P.G., O’Bryan, C.A., Martin, E.M., Pendleton, S., Shannon, E., Marcy, J. & Ricke, S.C. (2010). Dry Heat Thermal Inactivation of Listeria innocua on Deli Slicer Components. Food Protection Trends, 30 (9), 588-592.

[17] Flemming, H.-C., Neu, T.R. & Wozniak, D. (2007). The EPS matrix: the “House of biofilm cells”. Journal of Bacteriology, 189 (22), 7945–7947.

[18] Faille, C., Fontaine, F. & Bénézech, T. (2001). Potential occurrence of adhering living Bacillus spores in milk product processing lines. Journal of Applied Microbiology, 90 (6), 892-900.

[19] Faille C. T., Bénézech G., Midelet-bourdin Y., Lequette M., Clarisse G., Ronse, G., Ronse, A. & Slomianny, C. (2014). Sporulation of Bacillus spp. within biofilms: a potential source of contamination in food processing environments. Food Microbiology, 40, 64-47.

[20] Fryer, P.J. & Asteriadou, K. (2009). A prototype cleaning map: a classification of industrial cleaning processes. Trends in Food Science and Technology, 20 (6), 255-262.

[21] Holah, J. T. (2014) Cleaning and disinfection practices in food processing. Chapter 9. In L.M. Lelieveld, J. Holah and D. Napper (Eds.), Hygiene in Food Processing. Principles and practice. 2nd ed., Woodhead Publishing, Cambridge, pp. 259-304).

[22] ISO/TC 34/SC 17, ISO 22000, Management systems for food safety.

[23] ISO/TC 118, Subcommittee SC 4, ISO 8573-1:2010. Compressed air – Part 1: Contaminants and purity classes.

[24] Jensen, B.B.B., Friis, A., Bénézech, T., Legentilhomme, P. & Lelièvre, C. (2005). Local wall shear stress variations predicted by computational fluid dynamics for hygienic design. Transaction of the Institute of Chemical Engineers, Part C. Food and Bioproducts Processing, 83 (1), 1-8.

[25] Jones, I., Cullen, P.J. & Greene, A. (2012). Using PAT to support the transition from cleaning process validation to continued cleaning process verification. Journal of Validation Technology, 18 (1), 50-56.

[26] Kim, J.-G. & Yousef, A.E. (2000). Inactivation kinetics of foodborne spoilage and pathogenic bacteria by ozone. Journal of Food Science 65(3), 521-528.

[27] Kolari, M. (2003). Attachment mechanisms and properties of bacterial biofilms on non-living surfaces. Academic Dissertation, University of Helsinki, Finland, 79 p.

[28] Lelievre, C., Faille, C. & Bénézech, T. (2001). Removal kinetics of Bacillus cereus spores from stainless steel pipes under CIP procedure: influence of soiling and cleaning conditions. Journal of Food Process Engineering, 24 (6), 359-379.

[29] Lelièvre, C., Legentilhomme, P., Gaucher, C., Legrand, J., Faille, C. & Bénézech, T. (2002). Cleaning in place: effect of local wall shear stress variation on bacterial removal from stainless steel equipment. Chemical Engineering Science, 57 (8), 1287-1297

[30] Lequette, Y., Boels, G., Clarisse, M. & Faille, C. (2010). Using enzymes to remove biofilms of bacterial isolates sampled in the food-industry. Biofouling, 26 (4), 421-431.

[31] Luby, S., Jones, J., Dowda, H., Kramer, J. & Horan, J. (1993). Large outbreak of gastroenteritis caused by diarrheal toxin-producing Bacillus cereus. Journal of Infectious Diseases, 167 (6), 1452-1455.

[32] Majoor, F.A. (2003), ‘Cleaning-in-place’, Ch. 11, in Lelieveld, H.L.M., Mostert, M.A., Holah, J. & White, B. (eds.), Hygiene in Food Processing, 1st ed., Woodhead Publishing, Cambridge, England, pp. 197-219.

[33] Melo, L.F & Bott, T.R. (1997). Biofouling in water systems. Experimental Thermal and Fluid Science, 14 (4), 375-381.

[34] Middleton, K.E., Holah, J.T. & Timperley, A.W. (2003). Guidelines for the Hygienic Design, Selection and Use of Dry Cleaning Equipment, Guideline N° 44, Campden & Chorleywood Food Research Association, Chipping Campden, Gloucestershire, United Kingdom, pp. 1-41.

[35] Moerman, F. & Mager, K. (2016). Cleaning and disinfection in dry food processing facilities, Ch. 35, in: Lelieveld, H.L.M., Holah, J. & Gabric, D. (Eds.). Handbook of Hygiene Control in the Food Industry, 2nd ed., Duxford-Cambridge, United Kingdom, Woodhead Publishing/Elsevier, pp. 521-554.

[36] Phinney, D.M., Goode, K.R., Fryer, P. J & Heldman, D. & Bakalis, S. (2017). Identification of residual nanoscale foulant material on stainless steel using atomic force microscopy after clean in place, Journal of Food Engineering, 214, 236-244.

[37] Potter, L., Limburn, R., Gaze, J., Ballard, C., & and Leadley, C.E. (2017. Development of low Aw food and environmental decontamination: inactivation kinetics, R&D report no. 422, Chipping Campden, Gloucestershire, United Kingdom

[38] Schöler, M., Föste, H., Helbig, M., Gottwald, A., Friedrichs, J., Werner, C., Augustin, W., Scholl, S. & Majschak, J.-P. (2012). Local analysis of cleaning mechanisms in CIP processes. Food and Bioproducts Processing, 90 (4), 858-866.

[39] Stanga, M. (2010). Sanitation: cleaning and disinfection in the food industry. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 589 p.

[40] Stoodley, P., Sauer, K., Davies, D.G. & Costerton, J.W. (2002). Biofilms as complex differentiated communities. Annual Reviews in Microbiology, 56, 187-209.

[41] Tamime, A.Y. (2008). Cleaning-in-Place: Dairy, Food and Beverage Operations. 3rd ed., ISBN: 978-1-44430225-7, Blackwell Publishing, Oxford, United Kingdom, 250 p.

[42] Weidemann, C., Vogt, S. & Nirschl, H. (2014). Cleaning of filter media by pulsed flow - Establishment of dimensionless operation numbers describing the cleaning result. J. of Food Engineering, 132, 29-38.

[43] Wildbrett, G. (2006). Reinigung und Desinfektion in der Lebensmittelindustrie Auflage 2, Behr Verlag, Hamburg, Deutschland, 490 p.

[44] Mc Donnell, G., Denver Russell, A., Clinical Microbiology (1999). Antiseptics and Disinfectants: Activity, Action, and Resistance1999; P. 147-179

[45] Commercial Food Sanitation, SSOP in ‘General Documentation’ https://commercialfoodsanitation.com.

[46] Plett, E.A. & Graßhoff, A. (2007). Cleaning and Sanitation. Chapter 14 in Heldman, D.R. & Lund, D.B. (Eds.). Handbook of Food Engineering. 2nd Edition. CRC Press, Boca Raton. pp. 929-975.

Appendix 1: Key Learning Points

• Understanding differences in soil compositions and structures resulting in different behaviours during cleaning.

• Understanding of critical parameters required for effective wet cleaning based on the Sinner Circle.

• Basic understanding of cleaning agents and disinfection types available.

• Understanding most common wet and dry-cleaning techniques and tools

• Understanding most common disinfection methods

• Understanding key elements required for effective cleaning programmes.

Appendix 2: Certification Requirements

The equipment or processes described in this Guideline are not eligible for Certification.

Appendix 3: OPC Procedure Guidelines

1. Prepare the area to be cleaned:

i. Ensure the cleaning time window is adequate

ii. Ensure the appropriate resources are available:

- appropriate number of cleaning staff,

- correct chemicals at the right dilution,

- dedicated colour coded cleaning equipment, well cleaned and disinfected and in a good condition,

- chemical supply and dosing equipment, clean and in good working order,

- water temperatures correct for the cleaning process and the chemicals in use,

- correct clean personal protective equipment (PPE) available and in a good condition

iii. PPE should be selected in accordance with the information contained within the chemical supplier’s safety data sheets (SDS) and product information documents, and after the completion of a ‘control of substances hazardous to health’ (C.O.S.H.H) assessment by a suitably trained person. It is good practice to have dedicated PPE to each area so that cross-contamination risks are reduced.

iv. Assess the production to cleaning/disinfection handover to ensure the area is prepared for cleaning (product and packaging removed and stored away in their dedicated storage areas, production documentation and specifications are removed and stored safely, waste is removed to dedicated waste handling areas, equipment is cleared of high levels of gross debris).

v. Decontaminate materials, tools, and utensils when transferred from basic or medium hygiene to high hygiene areas.

vi. Place warning signs at the appropriate entrance points to highlight that cleaning is taking place.

vii. Switch off and isolate equipment electric or compressed air supplies.

viii. Remove items which require cleaning in washrooms (e.g., trays, euro bins) to their dedicated dirty equipment storage area.

ix. Parts derived from equipment that require dismantling according to applicable SOPs should be placed onto dedicated ergonomically and hygienically designed devices (e.g., trollies), tables or clean lined plastic pallets. This ensures that all surfaces are exposed to the cleaning agents and disinfectants.

x. Assign tasks to the hygiene personnel

2. Remove gross solids:

i. Remove gross debris from all surfaces, including dismantled parts and catch trays, using suitable colour coded cleaning equipment (e.g., scrapers, brushes, squeegees). Work from top to bottom to reduce spills of debris onto the floor. Place the debris into dedicated waste vessels.

Figure 12 - Personnel Protection Equipment, PPE (courtesy Halag Chemie)

ii. Collect any floor waste using colour coded floor cleaning utensils and place the debris into dedicated waste vessels.

iii. Remove the waste bags and containers from the area and place them into the dedicated waste handling area.

iv. Return waste vessels to the washroom facilities for cleaning.

v. Move the dismantled parts into the washroom facilities for cleaning.

vi. in accordance with the recommendations given by the original equipment manufacturer (OEM), use appropriate disposable disinfectant wipes to wipe over electrical and other water sensitive equipment requiring protection. Subsequently cover with clean protective covers.

vii. To avoid clogging of drains an assigned, experienced and well-trained operator should check and empty drain baskets before commencing the rinse stage.

3. Pre-rinsing:

i. Pre-rinse all equipment and adjacent wall surfaces, working from top to bottom. Working as a team, all personnel should rinse together, while taking care not to direct debris to the drain. The water temperature should be appropriate to the nature of the soil type being removed.

ii. When using rinse nozzles, ensure the correct nozzle is used for an efficient, effective and sustainable clean process.

iii. Ensure all dismantled parts are rinsed in a controlled environment e.g., washroom. No parts should come into contact with the floor.

iv. Check and empty the drain baskets into a dedicated waste vessel. This task should ideally be undertaken by an assigned, experienced and well-trained trained operator who is wearing dedicated colour coded PPE and using dedicated colour coded cleaning equipment.

v. Gently flush the drain parts and gullies with fresh water or rinse with low-pressure water. Place drain parts into a dedicated colour coded container, to ensure that the parts do not come into contact with the floor or other surfaces within the area.

4. Detergent Clean:

i. An assigned, experienced and well-trained operator using dedicated colour coded cleaning equipment should clean the drain components and drain channels with a dilute solution of detergent (as recommended by the chemical supplier) applying mechanical action. Return drain components.

ii. Working together as a team, apply foam detergent (as recommended by the chemical supplier) from bottom to top. Apply foam detergent onto walls, floors, drain covers and manufacturing equipment, and ensure that all areas are covered with an even layer of detergent. Where applicable, select the correct nozzle for an efficient, effective and sustainable cleaning process. Allow for ~20 minutes contact time (with regard to the appropriate contact times, follow recommendations given by the chemical supplier). Do not allow the detergent to dry onto surfaces, and therefore take care when applying detergent foam to warm surfaces (consult the chemical supplier).

iii. Mechanical action might have to be employed for critical items of equipment or where, historically, there have been issues with difficult to remove tenacious soil types. Also, floor surfaces should be scrubbed with detergent

iv. Clean dismantled parts with a suitable detergent, in a controlled environment (e.g., washroom).

5. Detergent Rinse:

i. An assigned, experienced and well-trained operator should gently flush the drain parts and gullies with fresh water or rinse with low-pressure water, while taking care that the parts do not come into contact with the floor or other surfaces within the area.

ii. Rinse all equipment and adjacent wall surfaces. Work as a team (all personnel rinsing together), from top to bottom.

iii. When using rinse nozzles, select the correct nozzle for an efficient, effective and sustainable rinsing operation.

iv. Rinse all dismantled parts.

v. Using dedicated colour coded small handheld squeegees to remove any pooling water from the equipment. This step is essential to prevent potential dilution of the disinfectant during the final disinfection stage.

vi. Using dedicated colour coded ceiling squeegees, remove any condensation on pipes/ceiling.

6. Monitoring & Inspection:

i. Carry out cleaning verification checks (e.g., visual assessment, ATP, etc.).

ii. Re-clean any areas if required.

iii. If required, an assigned, experienced, and well-trained operator should reclean the drains (washing hands and change of PPE should be considered)

7. Disinfection (and rinse, if required) & Reassembly:

i. Disinfect drain parts (at the recommended concentrations as advised by the chemical manufacturer) and reassemble drains.

ii. Working as a team, apply disinfectant (at the recommended concentrations as advised by the chemical supplier) to all exposed surfaces, working from top to bottom. Include walls and floors. Ensure disinfectant is in contact with surfaces for the appropriate length of time.

iii. When using disinfectant nozzles, select the correct nozzle for an efficient, effective and sustainable disinfection process.

iv. Ensure all dismantled parts are thoroughly disinfected

v. Reassemble equipment and re-disinfect surfaces after reassembly.

vi. Fogging can be used if required.

vii. Squeegee floor surfaces dry.

8. Prepare the area for hand back to production:

i. Remove any plastic sheeting from electrical and other water sensitive equipment, and re-wipe surfaces if they could have been cross-contaminated.

ii. Take cleaning equipment to the washroom, then clean and disinfect all items and leave to dry

iii. Clean and disinfect PPE and leave to dry.

iv. Complete final verification checks (e.g., microbiological swabbing, due diligence documents).

Appendix 4: Electrochemical Activation of Water Containing Sodium Chloride

On-site production of Hypochlorous Acid and Sodium Hydroxide using Electrochemical Activation (ECA)

Electrolysis, an electro-chemical method, transforms NaCl and H2O by passing a direct electric current through them. As a result, a solution of sodium hydroxide, hypochlorous acid, and various other chlorine compounds will be generated depending on the electrolysis conditions. This solution is also referred to as electrochemical activated water (ECA). The solution with the ionic species of sodium hydroxide is a catholyte and the solution with the species of hypochlorous acid with the other chlorine compounds is an anolyte. Keeping both solutions separate they can be used individually as either a cleaning agent (catholyte) or a disinfectant (anolyte). However, corrosivity must be considered for the anolyte disinfectant owing to its high chloride content. The catholyte cleaner generated is non-foaming and non-corrosive, though high concentrations can discolour nonanodized aluminium and live stone. The use of ECA generated solutions requires soft, purified water to ensure that there are no impurities that otherwise form side reactions, thus lowering the efficacy. Further, there are great differences in electrolytic cells and differences in the anolyte and catholyte that they produce. The most advanced systems produce an anolyte that remains stable for six months to a year, unlike anolytes produced by artefact ECA cell technology. Thus, ECA water is typically produced on-site.

SALTWATER SOLUTION

Negative chlorine and hydroxyl ions flow toward the anode

Positive hydrogen and sodium ions flow toward the cathode

The acidic and the alkaline solutions are stored in separate tanks, where they can be used as a cleaning agent or a disinfectant

HYPOCHLOROUS ACID SOLUTION DISINFECTION

SODIUM HYDROXIDE ALKALINE SOLUTION CLEANING

Figure 27 – Production of ECA water

Appendix 5: Biofilms

What is a biofilm?

In natural aquatic environments bacteria are predominantly not free floating but grow as multi-species communities attached to submerged surfaces (Kolari, 2003). A biofilm can be defined as a surface attached community of microorganisms growing embedded in a self-produced matrix of extracellular polymeric substances (EPS). The biofilm can be called a city of microbes and the EPS represents the house of the biofilm cells (Flemming et al 2007). The biofilm matrix is very difficult to remove once it is formed. Mechanical force is the best way to get rid of a biofilm matrix.

Figure 28 - The formation of a mature biofilm proceeds in several steps: 1. Transport to the surface and reversible adsorption; 2. Irreversible attachment to the surface; 3. Multiplication and production of EPS; 4. Maturation of the biofilm; 5. Detachment of bacteria from the biofilm (Stoodley et al., 2002).

The first step is the transportation to the surface (1) and initial adhesion which is reversible, and the bacterial cells can leave the surface and become planktonic (free-swimming) again. Contacting the surface initiates a complex differentiation program resulting in the synthesis of extracellular polymeric substances (EPS). In the second phase, the cells attach irreversibly (2) to the surface with the excreted EPS. The EPS is a mixture of polysaccharides, proteins, and DNA.

Once the bacterial cells are irreversibly attached to the surface they start to multiply (3) forming microcolonies. Specific genes are activated that promotes the building of the biofilm matrix (EPS-matrix) (3). The cells in the biofilm start to communicate with each other through cell-to-cell communication via chemical signals called quorum sensing.

As the biofilm matures (4) into a multilayer structure the quorum sensing gets more important. All the cells must be able to sense what is happening within the biofilm community and participate in the building of the biofilm structure. A mature biofilm is also three dimensional and often has a mushroom-like structure. To support the biofilm inhabitants with nutrients in the three-dimensional structure a transportation system within the biofilm must be established. The water content in a biofilm is about 85-95%. The EPS-polymers are highly hydrated and retain water in the biofilm (Flemming et al., 2007). For a biofilm, to reach full structural maturity it can take up to 10 days or more. Little is known about how much time is needed for the different steps in the biofilm formation.

In the 5th and last stage, a mature biofilm releases bacteria into the liquid phase (5). Release of bacteria from a surface can be seen in dairy systems long before a mature biofilm has been formed. This release could be due to the fact that the biofilm formation is still in the first reversible state or early in the second stage where all bacteria are not irreversibly attached to the surface.

How to get rid of biofilms

Thorough cleaning and disinfection of surfaces generally prevents the formation of biofilms. So as the major control, all surfaces should be cleaned. Biofilms tend to form in areas that are physically difficult to clean (e.g. beyond the easy reach of the cleaning operatives) or are inherently difficult to clean e.g. because of poor hygienic design.

Bacteria growing in a biofilm on a surface are generally more resistant to many anti-microbial agents, than the same bacteria growing in a free-swimming (planktonic) state (Kolari, 2003). In the food industry, biofilms may cause malfunctioning of equipment, reduce the efficiency of heat exchangers, and decrease the quality or safety of the end-product.

Once a mature biofilm is formed on the surface, it is very difficult to get rid of. Ordinary cleaning regimes usually kill the bacteria in the biofilm but are not able to remove the biofilm matrix. Mechanical force is the most efficient way to remove a biofilm matrix, but this is not possible in a closed system like pipes and heat exchangers. Oxidising chemicals like hydrogen peroxide or chlorine are often needed to remove biofilm matrix formed on surfaces (Christensen et al., 1990). But these compounds are often corrosive to the materials used in processing equipment. Enzymes, like different kinds of proteases, polysaccharidases and DNAse can also be used to remove the biofilm matrix (Lequette et al 2010).

Hypochlorite

Halogens

Oxidisers/ Peroxides

+ gram -

Appendix 6: Properties of Chemical Disinfectants

General Properties

Most effective at pH 6-7.5

Advantages

Relatively inexpensive; broad germicidal spectrum; reacting (short contact times) No decrease in effectiveness hard water Iodophors

Effective at pH ≤ 4 and at low temperature; not effective > 50°C and pH > 7

Effective at low concentrations and low temperature over a broad pH range

Effective at very low concentrations (< 0.4%) and low temperature over a broad pH range

Most effective at pH 8.5

Effective in the presence of soil (disinfection mats); no decrease in effectiveness in hard water

Broad germicidal spectrum; effect of hard water

Broad germicidal spectrum; fast (short contact times); limited effect of hard water; residuals decompose slowly to acetic oxygen and water;

Bbroad germicidal spectrum; reacting fast (short contact no formation of by-products; tainting than chlorine; little negative impact of high organic loads/hard water

Effective at low concentrations. For surface disinfection, ozonized water

Effective over broad pH range; not effective > 50°C

Effective at low concentrations

Cleaning and disinfection properties; enhanced effectiveness if QAC or diamines are present

Environmentally friendly, no residuals (decomposes to oxygen)

Taint free, non-corrosive, non irritating, heat stable

Taint free, non-corrosive

Only no-rinse disinfectant globally; facilitates drying of wet cleaned surfaces

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