The flavour of a food is one of its most important qualities. Edited by two leading authorities in the field, and with a distinguished international team of contributors, this important collection summarises the wealth of recent research on how flavour develops in food and is then perceived by the consumer. The first part of the book reviews ways of measuring flavour. Part II looks at the ways flavour is retained and released in food. It considers the way flavour is retained in particular food matrices, how flavour is released during the process of eating, and the range of influences governing how flavour is perceived by the consumer. Flavour in food guides the reader through a complex subject and provides the essential foundation in both understanding and controlling food flavour.
Taints
and off-flavours in foods
(ISBN 978-1-85573-449-4)
Taints and off-flavours are a major problem for the food industry. Part I of this important collection reviews the major causes of taints and off-flavours, from oxidative rancidity and microbiologically derived offflavours, to packaging materials as a source of taints. Part II discusses the range of techniques for detecting taints and off-flavours, from sensory analysis to instrumental techniques, including the development of new rapid, on-line sensors.
Colour in food – Improving quality
(ISBN 978-1-85573-590-3)
The colour of a food is central to consumer perceptions of quality. This important collection reviews key issues in controlling colour quality in food, from the chemistry of colour in food to measurement issues, improving natural colour and the use of colourings to improve colour quality.
Details of these books and a complete list of Woodhead’s titles can be obtained by:
• visiting our web site at www.woodheadpublishing.com
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Contents Contributor contact details
1 Modifying flavour: an introduction .
A. J. Taylor and J. Hort, University of Nottingham, UK
1.1 Introduction.
1.2 References.
2 Flavouring substances: from chemistry and carriers to legislation
D. Baines, Baines Food Consultancy Ltd, UK
2.1 The importance of olfaction in the appreciation of flavour.
2.2
2.3
2.5
G. Cravotto, University of Turin, Italy and P. Cintas, University of Extremadura, Spain
3.1 Introduction.
3.2
3.3
3.4 Continuous subcritical
3.5
3.6 Microwave-assisted extraction (MAE) .
3.7 Extraction in the analysis of flavours.
3.8 Drying methods and solvent distillation.
3.9 Conclusion.
3.10 Acknowledgements
3.11 References.
4 From fermentation to white biotechnology: how microbial catalysts generate flavours
R. G. Berger, Leibniz University of Hannover, Germany
4.1 Introduction.
4.2 Flavour formation along known pathways.
4.3 Flavours from complex substrates
4.4 White biotechnology
4.5 Future trends.
4.6 Sources of further information.
4.7 References.
5 New developments in yeast extracts for use as flavour enhancers .
B. Noordam and F. R. Meijer, DSM Food Specialties, The Netherlands
5.1 Introduction.
5.2 Developments in yeast extracts
5.3 Materials and methods.
5.4 Results and discussion.
5.5 Conclusions
5.6 References.
S. Serra, C.N.R. Milano, Italy
6.1 Introduction.
6.2 Chiral flavour – synthesis
6.3 Chiral flavour
6.4 Key flavour compounds.
6.5 Sources of further information and advice.
6.6 References.
7 Formulating low-fat food: the challenge of retaining flavour quality
J. Hort and D. Cook, University of Nottingham, UK
7.1 Introduction.
7.2 Lowering the fat content of food: what happens to the flavour?
7.3 Strategies for replacing fat in foods and the implications for flavour
7.4 Why is fat so hard to replace?
7.5 Representation of fat in the brain
7.6 Future trends.
7.7 References.
8 New pungent and cooling compounds for use in foods
C. C. Galopin, Givaudan Flavors Corporation, USA
8.1 Introduction.
8.2 History
8.3 Fundamental differences between chemesthetics and flavours.
8.4 Physiology
8.5 Common pungent chemicals and their activity
8.6 Common cooling compounds and their activity.
8.7 Future trends.
8.8 Conclusion.
8.9 References.
9 Controlled release of flavour in food products
G. Reineccius, University of Minnesota, USA
9.1 Introduction.
9.2 Industrial approaches for protecting flavourings from deterioration
9.3 Industrial approaches to achieve controlled release of flavourings.
9.4 Needs in flavour encapsulation/controlled release
9.5 Advice
9.6 References.
10 Developments in sweeteners
S. Kemp, Cadbury Schweppes, UK and M. Lindley, Lindley Consulting, UK
10.1 Introduction.
10.2 Mechanism of sweetness perception
10.3 Novel sweeteners
10.4 Sweetness potentiators.
10.5 Sweetness inhibitors.
10.6 Future trends.
10.7 Sources of further information and advice.
10.8 References.
11
J. B. Marcus, Kendall College, USA
11.1 Umami: what it is, what it does and how it works. .
11.2 Culinary history of umami in flavour enhancement .
11.3 Scientific background of umami in flavour enhancement.
11.4 How the culinary aspects and science of umami interact.
11.5 Asian condiments that impart umami taste and tasteactive components
11.6 Western foods that impart umami taste and tasteactive components
11.7 Other umami taste-activators.
11.8 Taste-active components and umami synergy
11.9 Umami formed in ripening, drying, curing, ageing and fermenting
11.10 Practical aspects of umami in consumer acceptance.
11.11 Consumer applications of umami.
11.12 Food technology applications of umami.
11.13 Umami applications that maximise flavour, food acceptance and food preference.
11.14 Umami applications for the development and enhancement of recipes and products.
11.15 US umami initiatives
11.16 European umami initiatives
11.17 Future trends.
11.18 Conclusion.
11.19 Sources of further information and advice.
11.20 References.
12 Bitter blockers in foods and pharmaceuticals
R. McGregor, Linguagen Corporation, USA
12.1 Introduction.
12.2 Why reduce bitterness in foods and pharmaceuticals?.
12.3 Current approaches to reducing bitterness.
12.4 Advantages to bitter blocked pharmaceutical formulations.
12.5 The science of taste perception
12.6 Identifying compounds that decrease the perception of bitterness.
12.7 Future trends.
12.8 Sources of further information and advice.
12.9 References.
13 Masking agents for use in foods
M. Gascon, Wixon Inc., USA
13.1 Introduction.
13.2 How masking agents work
13.3 Ingredients used to formulate masking agents.
13.4 What to consider when working with masking agents . .
13.5 Masking agents: when to use or not to use.
13.6 Outlook and perspectives
13.7 References.
14 Selecting the right flavourings for a food product
K. B. de Roos, Givaudan Nederland B.V., The Netherlands
14.1 Introduction.
14.2 Creation of the desired flavour profile
14.3 Stability of the flavouring
14.4 Solving flavour release problems
14.5 Solving flavour stability problems in products.
14.6 Future trends.
14.7 Sources of further information and advice.
14.8 References.
Contributor contact details
Chapter 1
A. J. Taylor
Professor of Flavour Technology
Division of Food Sciences
University of Nottingham
Sutton Bonington Campus
Loughborough
LE12 5RD
UK
e-mail: Andy.Taylor@nottingham. ac.uk and J. Hort
Lecturer in Sensory Science Division of Food Sciences
University of Nottingham
Sutton Bonington Campus
Loughborough LE12 5RD
UK
e-mail: joanne.hort@nottingham. ac.uk
Chapter 2
D. Baines
Baines Food Consultancy Ltd 22 Elizabeth Close Thornbury Bristol BS35 2YN UK
e-mail: db@bfc.demon.co.uk
Chapter 3
Giancarlo Cravotto*
Dipartimento di Scienza e Tecnologia del Farmaco University of Turin Via P. Giuria 9 I-10125 Torino Italy
e-mail: giancarlo.cravotto@unito.it and
Contributors
Pedro Cintas
Departamento de Química
Orgánica
Facultad de Ciencias
University of Extremadura
Avenida de Elvas s/n e-06071
Badajoz Spain
e-mail: pecintas@unex.es
Chapter 4
R. G. Berger
Leibniz University of Hannover Centre of Applied Chemistry Institute of Food Chemistry
Wunstorfer Strasse 14 D-30453 Hannover Germany
e-mail: rg.berger@lci.uni-hannover. de
Chapter 5
B. Noordam and F. R. Meijer
DSM Food Specialties
R&D/FTD/Application PO-box 1 2600MA Delft
The Netherlands
e-mail: Bert.Noordam@DSM.COM
Frank.Meijer@DSM.COM
Chapter 6
S. Serra
C.N.R. Istituto di Chimica del Riconoscimento Molecolare, presso
Dipartimento di Chimica
Materiali ed Ingegneria Chimica del Politecnico
Via Mancinelli 7 20131 Milano
Italy
e-mail: stefano.serra@polimi.it
Chapter 7
J. Hort* and D. Cook Division of Food Sciences University of Nottingham Sutton Bonington Campus Loughborough LE12 5RD
UK
e-mail: joanne.hort@nottingham. ac.uk
Chapter 8
C. C. Galopin
Givaudan Flavors Corporation Research and Development 1199 Edison Drive Cincinnati OH 45216
USA
e-mail: christophe.galopin@pmusa. com
Chapter 9
G. Reineccius
Dept. Food Science and Nutrition
University of Minnesota 1334 Eckles Ave
St. Paul MN 55108
USA
e-mail: greinecc@umn.edu
Chapter 10
S. Kemp
Head of Global Sensory and Consumer Guidance
Global Science Centre
Cadbury Schweppes
The Lord Zuckerman Research Centre
Pepper Lane
Reading RG6 6LA
UK
e-mail: sarah.e.kemp@rssl.com and M. G. Lindley
Lindley Consulting 17 Highway Crowthorne
Berkshire RG45 6HE UK
e-mail: mikelindley@btinternet.com
Chapter 11
J. B. Marcus
Kendall College School of Culinary Arts 900 N. North Branch Street Chicago Illinois 60622 USA
e-mail: JMarcus@Kendall.edu
fitfoodpro@aol.com
fitfoodpro@sbcglobal.net
Chapter 12
R. McGregor Linguagen Corp. 2005 Eastpark Boulevard Cranbury NJ 08512-3515 USA
e-mail: richard.mcgregor@ linguagen.com
Chapter 13
M. Gascon Wixon Inc. 1390 East Bolivar Avenue St Francis WI 53235 USA
e-mail: mariano_gascon@wixon. com
Chapter 14
K. B. de Roos De Eelinkes 37 7101 PZ Winterswijk The Netherlands
e-mail: k.b.de.roos@hccnet.nl
1
Modifying flavour: an introduction
A. J. Taylor and J. Hort, University of Nottingham, UK
1.1 Introduction
Modifying the flavour of foods by adding other materials is an ancient practice. The use of salt as a preservative, and as a flavour enhancer, has been practised for hundreds, if not thousands, of years. Similarly, the use of heat to cook food has its roots in antiquity and presumably made the food easier to eat (compare the texture of cooked meat versus raw) and more digestible (native starch is hard to digest compared with gelatinised). It also reduced the load of food poisoning organisms on the food and increased food safety while adding more volatile compounds to the flavour profile through chemical reactions such as caramelisation and the Maillard reaction. Today, we cook foods for all these reasons but we are more interested in the flavour aspect, as the other issues are no longer of primary importance, at least for that part of the world that has an adequate supply of food. Chefs routinely use herb and spice flavourings to complement the natural flavours of staple foods such as meat, fish and cereal products, and many popular dishes owe their characteristic flavour, not to the major ingredients, but to the minor added flavours. Thus modifying food flavour is a longstanding practice that has developed in response to various human factors, starting with our initial attempts to ensure survival of the human race but now focused more on the hedonics of food.
Food production and consumption patterns have changed markedly in Western society over the past few decades, with a move away from home cooking using basic ingredients, to mass-produced foods that can be ‘cooked’ at home simply by reheating in an oven. Convenience foods and preprepared meals form much of the average person’s diet and the scale and scope of food manufacture create different preparation techniques
compared with traditional cooking in the home, or restaurant cooking, both of which serve only a relatively small number of people. For example, scaling up the dishes prepared by development chefs is notoriously difficult as the whole time and temperature conditions of cooking can change. A good example is sauce manufacture where the come-up time (the time to reach the desired temperature) of a 2 tonne batch cooker is of the order of 60 min. This is followed by a cooking time and then further holding times during packing, meaning that products can be held at elevated temperatures for several hours. This change in thermal processing has a significant effect on the chemistries that produce or destroy flavour compounds, with the result that the flavour of a 2 tonne batch will not necessarily resemble the flavour of the 200 g sample from the development kitchen. One way of addressing this situation is to use the flavourings produced by flavour houses. They can be added to the batch late in the cook and the level of dosage can be varied to produce the desired flavour intensity. Another example of a mass manufacture challenge, is the necessity to maintain the flavour of foods during shelf-life and/or during the reheating cycle. The flavour industry has developed special forms of flavour to address the shelflife issue (e.g. encapsulated flavours) and has the knowledge to select flavour compounds that will perform better in reheating scenarios than the naturally occurring flavours. Added flavourings are also essential ingredients in the production of goods such as confectionery, beverages, cakes, biscuits and snack foods. In all these examples, the flavour of the base composition is modified in some way to deliver the desired properties to the foods. Although mass-produced foods are very popular, in some parts of the world, the food and flavour industry is facing a new challenge as consumer organisations raise questions about the quality of the mass-produced products. In an open society, this is a valid topic that should be debated in an open way. However, the tone taken by many of the consumer groups (and the media) is quite aggressive and is based on the premise that the food and flavour industries are providing unhealthy food and that they are only out to make money. In the United Kingdom, at least, rational discussion is largely missing from the newspaper and television coverage and, in these authors’ opinion, the interviewers rarely challenge the representatives of the consumer groups as to their credentials and their motives since, after all, many of these people are also making money and creating careers out of the situation. The message that consumers receive from these sources is that any food component considered synthetic must be bad and that anything natural must be good. Although irrational, this is a deeply rooted belief and is illustrated by a recent UK government pronouncement that ‘natural’ remedies can make health claims without going through the extensive testing procedures required for synthetic drugs (MHRA 2004).
Although the issues described above are non-technical and, although the assertion about unhealthy food and profit making is largely untrue, these issues have had a major effect on the attitude of consumers and also the
approach taken by food and flavour manufacturers. Some companies are changing product formulation so that all ingredients can be declared as natural. Other companies are exploring an approach that decrees that their products will be made using only ingredients that could be found in ‘the kitchen store cupboard’. Additives are thus excluded and only ingredients recognised by the consumer (e.g. salt, wheat flour, butter) can be used. These consumer-driven changes impact on the flavour industry in two ways. First, they are required to produce greater quantities of natural flavourings and, second, the debate about whether mass-produced natural flavourings will be considered as ‘kitchen store cupboard’ ingredients (and therefore accepted by consumers) remains to be settled. In this latter case, maybe the common domestic usage of flavourings such as vanilla extract will lead to a certain level of acceptance. Another current, associated concern is the problem of obesity in many Western countries. There is considerable pressure on food manufacturers to produce foods with reduced amounts of fat, salt and sugar to address the nutritional guidelines issued by governments. However, the new products have to taste just as good as the originals or the population will not consume them and therefore will gain no nutritional benefit.
The paragraphs above largely describe the market factors that influence flavour production and marketing, commonly called ‘market pull’. There is also a complementary, research-led ‘push’ which influences flavour production and it is interesting to examine how research findings have influenced the way that flavours are developed commercially. Such an examination is subjective and the following topics are the editors’ interpretation of research progress since 1995.
The most notable development is our increased understanding of the flavour receptors in the nose and mouth. Buck and Axel received the 2004 Nobel prize in Physiology and Medicine for their work on olfactory receptors, an award that raised the profile of flavour research worldwide. Parallel work on the taste receptors, and the associated transduction mechanisms, have increased our knowledge of the way tastants act on the system. These advances have resulted in some direct applications, for example, the Senomyx and Linguagen companies in the United States are using knowledge of the taste receptors, coupled to molecular biology techniques, to screen compounds for various taste activities, such as the ability to block bitterness or to enhance flavour. Other potential applications will need more knowledge on the systems biology of the taste and smell systems. Examples of these applications are an understanding of aroma interactions at the receptor level (i.e. how does one odour molecule affect the binding of a different odour), the dynamics of binding, the potential interactions between neural signals as they are processed at the different levels in the brain and, the ultimate goal, an understanding of why a particular mixture of aroma and taste compounds produces such strong emotions when sensed.
Knowledge of the mechanisms and kinetics of the Maillard reaction have also advanced, thanks to the application of new analytical and data processing tools. The pathways of reactants can be followed using labelling techniques such as CAMOLA (Schieberle, 2005) while on-line monitoring of the process can be achieved (Channell and Taylor, 2005; Pollien et al., 2003). Models of the Maillard reaction, which predict the products from different reactant levels and different processing conditions, are also being developed (Martins and Van Boekel, 2005). There are obvious applications for these techniques in optimising thermal flavour production or in controlling the amounts of undesirable products such as acrylamide and 3-chloro-propan1,2-diol (MCPD).
The way in which flavour components modify the perceived flavour of foods has also advanced from a stage where we were simply aware of the situation, to an understanding of the interactions involved at a qualitative and quantitative level. Many examples exist in the literature but the observation that the perceived flavour of a solution decreases as viscosity increases, illustrates the point well (Pangborn and Szczesniak, 1974). One of the original explanations for this behaviour was that viscosity hindered the release of aroma from the sample when eaten and caused a decrease in aroma signal. This hypothesis was disproved (Hollowood et al., 2002) and, coupled with work from other laboratories, reinforced the idea that flavour was a multi-modal construct in which cross-modal interactions were significant. The seminal work of Dalton et al. (2000) who showed that subthreshold levels of benzaldehyde and sweetener interacted cognitively to produce a perception, has been complemented by data from our laboratory on taste – aroma and taste – viscosity – aroma interactions in sweet and savoury flavour (see for example Davidson et al., 1999; Pfeiffer et al., 2005). We now know that tastant release is altered in viscous solutions and the change in sensory properties is caused by a reduced taste–aroma interaction. Commercial examples of this knowledge are now evident, such as the recently launched chewing gum in the United States with the ‘ridiculously long-lasting flavour’ (Cadbury Adams, Stride gum). The prolonged flavour sensation seems to work by delivering sugar over a longer time period to enhance the sensation of mintiness as suggested previously (Davidson et al., 1999). Other, not so obvious, applications are in confectionery and reduced fat foods. The result is that the principles of multi-modal flavour perception have been established through fundamental research and are now being used by industry to address real needs; this is the ultimate goal of applied scientific research and is gratifying to see the loop being closed. With the ready availability of analytical methods to monitor flavour release in vivo (Linforth and Taylor, 2003) and for brain imaging to investigate cognitive interactions between taste and aromas (Verhagen and Engelen, 2006), further progress in our understanding is envisaged.
For the reasons outlined above, the manufacture, development and uses of flavourings are driven by a very wide range of economic, scientific, legal
and social factors. The current needs for modifying flavour are therefore different from those experienced by the industry in the mid-1990s and the content of this book attempts to address some of the issues that are relevant at the current time. The flavouring industry has used technology to develop a range of pleasant flavours with high flavour potency that can be used to modify the overall flavour of a product. The development of those technologies has formed the basis for R&D in flavour houses across the world and has led to novel and improved ways of modifying the flavour of foods to meet the needs of industry and consumers.
The book starts with an account of how the flavour industry has developed its technology over the past century or so (Chapter 2; Baines). The initial focus on chemical synthesis of the flavour compounds found in nature created an innovative industry which improved the flavour, and the general quality, of foods from the turn of the 20th century. This was followed by the adoption of the newly discovered separation and identification techniques in the 1960s to extract new flavour compounds from natural materials and then synthesise analogues to overcome the problems associated with natural sources, such as seasonality and variations in flavour content. The current trend is for ‘natural’ flavours and ingredients and, in some countries, this is being pursued to a very high level. Baines finishes his chapter by pointing out that the current EU legislation is likely to favour the development of new flavours in markets outside the EU, owing to the costs and complications of clearing new flavouring compounds for use in the EU.
With the consumer pressure for natural food ingredients, the next two chapters tackle the production of natural flavours (Chapters 3 and 4). This could be considered as modifying the form in which the flavour is delivered, i.e. using natural means to manufacture the flavours rather than organic chemical syntheses. Chapter 3 is concerned with the extraction of natural flavourings from plant materials and how the new extraction techniques can provide high-quality materials while also meeting the additional needs of protecting the environment and ensuring sustainability. The use of solvents such as supercritical carbon dioxide and pressurised water has many environmental attractions as they are natural and non-toxic agents. Like many potential solutions to the problems of energy and environment, the full impact of these techniques has not been fully considered, e.g. although CO2 is environmentally friendly, how much extra energy do we spend extracting, compressing, transporting and applying CO2 in the extraction of flavours? It will need a bigger book than this to fully discuss these issues but the adverse energy requirements of bioethanol production have already shown the potential problems of these ‘green’ technologies. Chapter 4 describes new advances in biotechnology to produce natural flavours in a vast array of microorganisms, using our advanced knowledge of metabolic pathways which can now be expressed in most any organism through genetic modification. It is ironic that while genetically modified food is not acceptable to
some sections of Europe, drugs and flavours produced by these means are totally acceptable.
The extraction of tastants from yeast is described in Chapter 5. Yeast extracts are well known for their meaty and savoury (bouillon) flavour properties but new methodology delivers yeast extracts with little or no savoury flavour and with very interesting enhancing properties. This is an exciting development as the components of these yeast extracts seem to exert a cross-modal effect on some unexpected sensory attributes, e.g. the mouthfeel of a low-fat dairy product.
The next set of chapters represents some of the more fundamental research work that will provide the future scientific knowledge for further innovations by the flavour industry. Chapter 6 describes fundamental work on the chirality of flavours and it has long been recognised that stereoisomers of certain compounds have different odours, with menthone being the classic example (Fisher and Scott, 1997). However, with the consumer demand for natural flavours, there is also a drive to mimic as closely as possible the form in which flavours are found in nature. The authors of Chapter 6 remark that although consumers apparently want their flavours to be natural, the costs of delivering flavour enantiomers that match the natural state will have to be accepted by the consumer first; then the industry will need to establish the feasibility of the current laboratory-scale methods for large-scale production. This chapter neatly illustrates how the development of technologies depends very much on the potential markets and is an example of an area where technology is available at a fundamental level but where the ‘market pull’ is not yet established.
In Chapter 7, the role of fat in food flavour is discussed from the fundamental point of view. The basic tenet is that fat has many roles in our appreciation of flavour quality. We know of its role in the partition (and therefore the release) of aromas, in the viscosity of the food as well as the all-important, but difficult to define, aspect of mouthfeel. Thus, if fat content in a food is changed, we can expect a host of effects on sensory quality and we will need not just a single fat replacer but a range of adjustments to recreate the many properties contributed by fat to a food’s overall flavour and acceptance. Indeed, the authors of this chapter question whether manufacturers will ever be able to replace fat successfully considering how adept the sensory mechanisms of the human body are at detecting fat. Therefore, applying this knowledge to the commercial situation, it seems that if we want to make a low-fat analogue of an existing product, we need to add a range of materials to fully replace fat in foods. While this may create a technical solution, it is unlikely to meet the consumer demands for ‘additive-free’ food products. The alternative solution is to create new food products with lower fat levels and a different flavour from conventional products. There are signs of both types of activity in the food area. New microstructures patented by Unilever (see, for example, Appelquist et al 2000) were designed to decrease fat content while maintaining effective
flavour delivery and demonstrate the development of new food structures. The development of new low-fat products can be seen in many supermarkets where clearly identified product ranges have been developed and marketed using words such as ‘lite’ or ‘low-fat’ to differentiate them from conventional products.
The next chapter in this section (Chapter 8), addresses the subject in a fundamental way by considering how pungent and cooling sensations are perceived by humans. With this knowledge, methods for manipulating the sensation by using appropriate structures and delivery mechanisms can be postulated and trialled. Linked to this is the concept of controlling flavour delivery to elicit optimum and novel flavours. Although flavour delivery can be easily controlled in model systems to study fundamental aspects of flavour perception (Hort and Hollowood, 2004), controlling delivery in real foods is much more difficult. Factors such as cooking and oral processing (e.g. mastication and hydration) can remove the effects of some delivery systems and cancel out any potential advantage. Reineccius (Chapter 9) reviews the methods currently available to modify the delivery of flavours through encapsulation techniques and gives examples of applications where encapsulation offers advantages.
The next group of chapters (Chapters 10–13) describes methods and materials to modify flavours, by masking or enhancement. One of the main applications for these techniques is the result of food reformulation to reduce fat, salt and sugar in our diet or to add components considered as nutritionally beneficial such as fibre or antioxidants which have inherent poor taste properties. Despite the simplistic view of some government agencies that meeting nutritional requirements is simply a question of adding or removing components from food, manufacturers and flavour houses who want to satisfy consumers’ flavour expectations know differently. Changing food formulations in this way creates flavour imbalance, and sensory analysis often identifies flavour defects such as bitterness or poor mouthfeel, which adversely affect the overall flavour of foods.
The first topic to be addressed is the use of sweeteners in food. Although considerable advances have been made in identifying alternatives to sucrose, the economic manufacture of foods with the same clean taste quality and temporal sweetness as sucrose eludes researchers. Chapter 10 reviews a range of compounds that have been investigated for their sweet taste. Some mention is also given to those compounds that may suppress sweetness, enabling the use of sucrose for its other functional properties without adding sweetness.
Although only recently recognised as the fifth taste, umami with its flavour-enhancing capability has been recognised in culinary circles for centuries. In Chapter 11, Marcus summarises what is known about the compounds and sensory mechanisms involved in umami sensation. She catalogues the presence of umami compounds in a wide range of foods and illustrates particular ingredients that are used in cooking that make use of
umami to optimise flavour. The information in this chapter complements some of the material presented in Chapter 5 on the flavour-enhancing properties of yeast extracts.
The next two chapters investigate the use of blocking or masking agents to modify the flavour of foods. In Chapter 12, McGregor reviews the current approaches taken to reduce bitterness and highlights how an increased understanding of taste receptor mechanisms can, and will continue to, advance the identification of suitable bitter blockers. In Chapter 13 Gascon outlines some of the masking agents available in the industry’s ‘toolbox’. However, more importantly, he highlights the fact that every product is likely to need its own unique ‘masking’ solution and that the use of blends of masking agents is more likely to be the solution. Without doubt, masking bitterness is a major challenge to both the food and pharmaceutical industry.
Many of the previous chapters of the book have addressed modifications to the production of flavours to meet the needs of consumers or to modify flavours as a result of reformulation. However, combining these flavour ‘raw materials’ into successful commercial flavours that will function in a wide variety of foods is a major task. In Chapter 14, the science behind the design of flavours that will function in the different food matrices is explained from the commercial angle by de Roos. Our understanding of how flavour is released from foods, before eating and during eating has advanced considerably over the last 10 years and it is satisfying to see these basic principles being applied and further developed to improve food flavours. This is an area in which one of the editors has had a significant interest and it is interesting to see how much the field has changed since an early review (Taylor, 1996).
Besides introducing the current work on modifying flavour to meet market and consumer needs, the chapters collectively demonstrate the breadth of scientific disciplines used in flavour production and application. Extraction involves principles of chemical engineering, physical and organic chemistries, bioprocessing brings together biochemistry and molecular biology, while chirality needs sophisticated analyses coupled to organic syntheses. The development of the various agents used to enhance or mask flavours requires knowledge of flavour perception at a receptor and cognitive level, coupled with the ability to produce compounds and materials that can deliver the necessary properties at an economic price. Moving on to the later chapters, we see that the role of human physiology during the eating of food also needs to be considered. For many researchers in the food area, it is this diversity that makes the field so interesting and, at times, so difficult. The diversity of sciences involved also reinforces the widely held view (see summary in Section 9.5) that significant advances in flavour will only be made through multi-disciplinary teams where all members have some awareness of other scientific disciplines.
1.2 References
appelquist, i. a. m., brown, c. r. t., homan, j. e., jones, m. g., malone, m. e., norton, i. t., appleqvist, i. a. and brown, c. r. (2000), ‘Low-fat food emulsions for e.g. spreads, dressing or mayonnaise, have gel particles for delaying the release of the flavor molecules’, Patents WO200007462-A, EP1102548-A, WO200007462-A1, EP1102548-A1, EP1102548-B1.
channell, g. a. and taylor, a. j. (2005), ‘On line monitoring of the Maillard reaction using a film reactor coupled to ion trap mass spectrometry’. Process and reaction flavors. Weerasinghe, D. K. and Sucan, M. K. Washington, DC, American Chemical Society. 905, 181–191.
dalton, p., doolittle, n., nagata, h. and breslin, p a s. (2000), ‘The merging of the senses: Integration of subthreshold taste and smell.’ Nature Neuroscience, 3 (5), 431–432.
davidson, j. m., hollowood, t. a., linforth, r. s. t. and taylor, a. j. (1999), ‘The effect of sucrose on the perceived flavour intensity of chewing gum.’ Journal of Agricultural and Food Chemistry, 47, 4336–4340.
fisher, c. and scott, t. r. (1997), Food Flavours: Biology and Chemistry. Cambridge, Royal Society of Chemistry.
hollowood, t. a., linforth, r. s. t. and taylor, a. j. (2002), ‘The effect of viscosity on the perception of flavour.’ Chemical Senses, 27, 583–591.
hort, j. and hollowood, t a. (2004), ‘Controlled continuous flow delivery system for investigating taste–aroma interactions.’ Journal of Agricultural and Food Chemistry, 52, 4834–4843.
linforth, r s t. and taylor, a j. (2003), ‘Direct mass spectrometry of complex volatile and non-volatile flavour mixtures.’ International Journal of Mass Spectrometry, 223–224, 179–191.
martins, s. i. f. s. and van boekel, m. a. j. s. (2005), ‘Kinetics of the glucose/glycine Maillard reaction pathways: influences of pH and reactant initial concentrations.’ Food Chemistry, 92 (3), 437–448.
mhra (2004), Medicines and Healthcare products Regulatory Agency, http://www. mhra.gov.uk/home.
pangborn, r. m. and szczesniak, a. s. (1974), ‘Effect of hydrocolloids and viscosity on aromatic flavour compounds.’ Journal of Texture Studies, 4, 467–482.
pfeiffer, j., hort, j., hollowood, t a. and taylor, a j. (2005), ‘Temporal synchrony and integration of sub-threshold taste and smell signals.’ Chemical Senses, 30, 1–7.
pollien, p., lindinger, c., yeretzian, c. and blank, i. (2003), ‘Proton transfer reaction mass spectrometry, a tool for on-line monitoring of acrylamide formation in the headspace of Maillard reaction systems and processed food.’ Analytical Chemistry, 75 (20), 5488–5494.
schieberle, p. (2005), ‘The carbon module labeling (camola) technique: a useful tool for identifying transient intermediates in the formation of Maillard-type target molecules.’ Annals of the New York Academy of Sciences, 1043, 236–248.
taylor, a. j. (1996), ‘Volatile flavor release from foods during eating.’ Critical Reviews in Food Science and Nutrition, 36 (8), 765–784.
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Flavouring substances: from chemistry and carriers to legislation
D. Baines, Baines Food Consultancy Ltd, UK
2.1 The importance of olfaction in the appreciation of flavour
The appreciation of flavour is realised through our chemical senses of olfaction and gustation and, to a lesser extent, through certain molecules that interact with trigeminal nerves located in the mouth, throat and nasal cavity. The trigeminal effect, or chemesthesis, is a minor but integral part of the flavour sensation involving the pain receptors that sense, for example, the heat from chillies, the cooling from peppermint and the burning from horseradish.
2.1.1 Gustation
Gustation, or the sense of taste, is experienced through five types of interaction in the mouth; sweetness, sourness, bitterness, saltiness and ‘umami’, the latter being the Japanese word for succulence or deliciousness and elicited by the salts of glutamic acid, ribonucleotides and a few other taste active chemicals (Bell and Watson, 1999; Dewis, 2005). Taste responds primarily to non-volatile, water-soluble or saliva-soluble flavouring substances and serves a number of purposes. It monitors the quality of food through the sweet and umami taste receptors which respond to the presence of sugars and glutamate respectively. Detecting sugars determines carbohydrate quality and the supply of energy, and the detection of glutamate determines protein quality and the supply of essential amino acids for healthy metabolic functioning. The bitter and sour receptors serve a protective role and defend the body from noxious and poisonous substances and the regulation
of sodium chloride in the bloodstream is facilitated by the salty taste receptor.
2.1.2 Olfaction
Our real ability to appreciate flavour, and to discriminate and understand the subtleties and nuances of foods and drinks, lies mainly with olfaction and is due to a quite amazing organ, the olfactory epithelium, which detects volatile organic chemicals in the environment and flavouring substances in food. This organ, located high in the nasal cavity, is a forward projection of the brain that interfaces with the outside world. It would have been one of the first organs to develop, even before the brain, and its original function would have been to detect chemical nutrients in an aqueous environment necessary for the survival of the organism. The olfactory epithelium has therefore had a very long time to evolve (Stoddart, 1999) and its ability to detect volatile organic chemicals is highly developed and tuned into the flavouring substances that are important in the foods we eat.
It is estimated that the olfactory epithelium can detect and discriminate around 10 000 different smells through around 6 million receptor cells which are replaced by the body every 4–10 weeks (Mackay-Sim and Kittel, 1991; Key, 1999). These olfactory receptor cells each possess several hair-like structures called cilia which protrude into a mucous layer covering the olfactory epithelium. The cilia act as ‘docking ports’ for the volatile flavour substances that evaporate from the tongue and throat into the nasal cavity and absorb into the olfactory mucus during the process of eating and drinking. The flavour chemicals absorbing in the mucous layer couple with specialised olfactory binding proteins located in the ciliary membrane (Buck and Axel, 1991). A signal then passes to the olfactory bulb where it is amplified and the ‘signal to noise’ ratio minimised before being relayed to the olfactory cortex in the limbic brain where it is interpreted. The limbic system is the most ancient part of the brain and is also involved with emotion, mood, sexual behaviour, reproductive control and fear. Smells play a number of important roles through the limbic system such as neonatal bonding, flight response from prey, the selection of a mate and the monitoring of food. Smells can evoke memory and emotions, trigger fear, influence mood and are important for our enjoyment when eating.
The ability of the olfactory epithelium to detect and interact with flavouring substances varies by many orders of magnitude and compared with gustation it is highly developed. If we compare the sensitivities of aroma and taste, our ability to detect sweetness through sugar is of the order of 3400 parts per million, the threshold level at which ordinary people start to detect sugar in water. If we relate this to time, which is easier to conceptualise, it is equivalent to approximately 1 second in an hour. By comparison, our ability to detect volatile flavouring substances is many orders of magnitude more sensitive and the flavouring substance with the lowest recorded
threshold, maple furanone, has a threshold in water of 0.00001 parts per billion, which equates to a time scale of 1 second in 3.2 million years. Humans have an extraordinary ability to perceive and discriminate between thousands of volatile organic compounds and an astonishing sensitivity to certain molecules that in evolutionary terms have been an important aspect in the survival of the species. Such is the amazing chemistry, biochemistry and neurobiology of the olfactory epithelium; nanotechnology in action initiated by flavouring substances in food and other volatile organic chemicals in the environment.
Our flavour senses are more complex than the simplistic overview described above and recent research has revealed that flavour perception is multisensory in nature, where one sensory input can modify the perception of another, showing that olfaction, gustation and chemesthesis are strongly interactive. A number of excellent texts are available describing olfaction, gustation and the multimodal relationship that exists between the senses in more detail, and the reader is directed to these for further information (Bell and Watson 1999; Taylor and Roberts 2004).
2.2 Flavouring substances in foods
Enormous progress has been made since the 1960s with the identification of volatile organic compounds in foods. In 1965 approximately 700 had been found but today the number of discrete volatile organic compounds detected in foods stands at over 7670; these are listed in the Nutrition and Food Research Institute of the Netherlands (TNO) publication website Volatile Compounds in Foods (VCF) (http://www.vcf-online.nl). The VCF register is the recognised world authority on the occurrence of volatile compounds in food and the latest version, 9.1, lists over 680 food sources in which flavouring substances have been identified. The compounds listed in the VCF have only been included if the validity of the identification has been authenticated by two methods of analysis, usually a retention time and a mass spectrum, and more than 105 700 individual occurrences are now registered in the database. Over 1000 discrete volatiles have been found in coffee and nearly the same number in beef. Many organic volatiles are ubiquitous across foods, while others are specific to a particular food group or even an individual food. It is this that makes the subject so fascinating and challenging for flavour chemists to identify which of the volatile organic compounds in foods are actually creating the flavour signals in the human brain that allow us to recognise the flavour of the food we eat.
Not all volatile compounds found in food can be classified as flavouring substances because some do not possess distinctive aromas, while others have very high odour thresholds and are not detected among other lower threshold flavouring substances present in foods. Others may have undesirable aroma profiles and some volatile compounds found in food cannot be
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