Introduction to food science and food systems 2nd edition parker solutions manual

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Chapter 10: Cold Learning Domain - Cognitive Level of Learning – Comprehension Time Allocation – Approximately 55 minutes Learning Objectives: • • • • • • •

Compare cooling, refrigeration, and freezing.

Identify four requirements for refrigeration.

Correlate storage temperature to length of storage.

Understand requirements for refrigeration and freezing.

List three methods of freezing.

Describe changes in food quality that may occur during refrigeration or freezing.

Compare home freezing to commercial freezing.

Vocabulary Introduced: • • • • • • • •

cool storage cryogenic freezer burn hydrocooling hypobaric immersion freezing refrigeration vacuum cooling

Needed Equipment/Materials: Instructor: PowerPoint presentation equipment Student: paper, pencil References: Introduction to Food Science and Food Systems, Second Edition

I.

Introduction [ Time Allocation: 5 min.]

A. Cold (cool) storage, refrigeration, and frozen storage are methods of food preservation and processing B. Various methods are used to take food to temperatures necessary for cold storage or frozen storage Reference: Introduction to Food Science and Food Systems, p. 153 Slide: 10-4

II.

Refrigeration Versus Freezing [ Time Allocation: 5 min.]

A. Overview 1. Types of storage a. Cool storage temperatures are 68 °F to 28 °F (16 °C to –2 °C) b. Refrigerator temperatures are 40 °F to 45 °F (4.5 °C to 7 °C) c. Frozen storage temperatures re 32 °F to 0 °F (0 °C to –18 °C) 2. Microbe growth a. Microbes grow rapidly at temperatures above 50 °F (10 °C) b. Some growth occurs at subfreezing temperatures as long as water is available c. Little growth occurs below 15 °F (–9.5 °C) 3. Refrigeration a. The first mechanical ammonia refrigeration system was invented in 1875 b. In the 1920s, Clarence Birdseye started frozen food packaging Reference: Introduction to Food Science and Food Systems, p. 153 Slide: 10-5

III.

Refrigeration and Cool Storage [ Time Allocation: 10 min.]

A. Overview 1. Cool storage is the gentlest of all food-preservation methods a. It affects taste, texture, nutritive value, and color the least b. However, it is only a short-time preservation method 2. Refrigeration is also a gentle method of food preservation a. It has minimal effects on the taste, texture, and nutritional value of foods

b. For most foods, refrigeration extends the shelf life by a few days or week c. Refrigeration slows down but does not stop the spoilage of food d. Refrigeration temperature is a key factor in predicting the length of storage time i. Household refrigerators usually run at 40.5 °F to 44.6 °F (4.7 °C to 7 °C) ii. Commercial refrigerators operate at slightly lower temperatures iii. Microorganisms called psychrophilics will grow at refrigeration temperatures 3. The timelines of refrigeration and food processing require that heat be rapidly removed from foods at harvest or slaughter a. This is accomplished through methods of moving air: i. Hydrocooling ii. Vacuum cooling iii. Liquid nitrogen B. Requirements of Refrigerated Storage 1. Refrigerated storage requires: a. Low temperatures b. Air circulation c. Humidity control (80% to 95%) d. Modified gas atmosphere 2. Other factors can affect the requirements: a. Insulation b. Frequency of door opening c. Quantity of hot product added daily d. Respiration rate of the food product 3. In controlled atmosphere storage: a. Standard temperatures and humidity are maintained b. Oxygen levels are reduced c. Carbon dioxide levels are elevated 4. Some controlled atmosphere storage units are hypobaric a. The pressure is also reduced b. This reduces the availability of oxygen C. Changes in Food During Refrigerated Storage 1. During refrigerated storage, foods can experience: a. Chill injury b. Flavor (odor) absorption c. Loss of firmness, color, flavor, and sugar 2. Refrigeration is not good for every food Reference: Introduction to Food Science and Food Systems, pp. 153-154 Slides: 10-6 through 10-9

IV.

Freezing and Frozen Storage [ Time Allocation: 15 min.]

A. Overview 1. Freezing can be thought of as a continuation of refrigeration 2. The freezing point for food is below the freezing point for pure water (32 °F [0 °C]) a. Solutes in water will lower its freezing point b. Water contained in foods has many solutes, mainly salts and sugars 3. Freezing, like refrigeration, will not destroy microorganisms or inactivate enzymes but only slow their deteriorative effect a. In some cases, it will completely inhibit the activity of microorganisms, even though they will still be alive b. Enzymes, on the other hand, will maintain a certain level of activity during freezing i. Food processors blanch vegetables prior to freezing them ii. Blanching, a mild heat treatment, inactivates enzymes 4. Food processors freeze foods to an internal temperature of 0 °F (–18 °C) a. The food must be maintained at this temperature or slightly lower during transport and storage b. Many fruits and vegetables will retain good quality at the above temperature for as long as 12 months and even longer B. Chemical Changes During Freezing 1. Enzymes in vegetables a. Blanching, as previously noted, inactivates enzymes in vegetables i. The vegetable must be rapidly cooled in ice water ii. This prevents further cooking b. Blanching helps destroy microorganisms on the surface of vegetables c. Overblanching i. Results in A cooked product ii. Loss of flavor, color, and nutrients d. Underblanching i. Stimulates enzyme activity ii. Is worse than no blanching at all 2. Enzymes in fruits a. Enzymes in fruits can cause browning and loss of vitamin C i. They are not usually blanched ii. The use of chemical compounds, such as ascorbic acid (vitamin C) is used to controls enzymes in frozen fruit b. Some temporary measures are used to control browning

i.

Such temporary measures include placing the fruit in citric acid or lemon juice solutions or in a sugar syrup ii. These methods do not prevent browning as effectively as treatment with ascorbic acid 3. Rancidity in foods a. Another chemical change in frozen products is the development of rancid flavors i. This occurs when fat, such as that found in meat, is exposed to air over a period of time b. Using a wrapping material that does not permit air to reach the product can control rancidity C. Textural Changes During Freezing 1. Overview a. Freezing consists of freezing the water contained in the food b. When the water freezes, it expands and the resulting ice crystals cause the cell walls to rupture c. Consequently, the texture of the product will be much softer when the product thaws d. This is not as apparent in products that are cooked before eating because cooking also softens cell walls 2. Rate of freezing a. Freezing products as quickly as possible can control the extent of cell wall rupture b. Some home freezer manuals recommend that the freezer temperature be set at the coldest setting several hours 3. Changes caused by fluctuating temperatures a. Storing frozen foods at temperatures higher than 0 °F i. Increases the rate at which deterioration can take place ii. Can shorten the shelf life of frozen foods b. Fluctuating temperatures i. Causes smaller ice crystals form larger ones ii. Can also cause water to migrate from the product 4. Moisture loss a. Ice crystals evaporating from the surface area of a product produces freezer burn i. A grainy, brownish spot where the tissues become dry and tough that typically develop off-flavors ii. Also caused by ice evaporating out of a frozen food b. Packaging i. Airtight packaging can limit freezer burn ii. Heavyweight, moisture-resistant wrap prevents it c. Avoiding thawing and refreezing reduces freezer burn D. Microbial Growth in the Freezer 1. Freezing does not destroy microorganisms a. Although blanching destroys some, sufficient numbers remain to multiply and cause spoilage when it thaws

b. Carefully inspect frozen products that have accidentally thawed 2. Clostridium botulinum, does not grow and produce toxin at 0 °F a. Freezing provides a safe and easy alternative to pressure canning low-acid foods E. Freezing Methods 1. Freezing methods that freeze the product in air include: a. Still-air sharp freezer b. Blast freezer c. Fluidized-bed freezer 2. Freezing methods where the food or food packages directly contact a surface that is cooled by a refrigerant include: a. Single-plate b. Double-plate c. Pressure-plate d. Slush freezer 3. In immersion freezing, intimate contact occurs between the food or package and the refrigerant; such as: a. Heat-exchange fluid b. Compressed gas c. Refrigerant spray 4. Extremely rapid freezing requires liquid nitrogen, a cryogenic liquid F. Packaging 1. Packaging protects against dehydration, light, and air 2. It needs to be strong, flexible, and liquid tight Reference: Introduction to Food Science and Food Systems, pp. 155-159 Slides: 10-10 through 10-15

V.

New Developments [ Time Allocation: 5 min.]

A. Overview 1. Food processors can prepare complete meals and freeze them until the consumer is ready to thaw and heat them 2. Many of these meals are sold in their serving dishes a. Meat and pasta dishes as well as seafood and vegetables are all available as frozen meals b. Other popular frozen foods are pot pies, pizza, desserts, breads, and potatoes 3. Many options boast healthy choices a. They are advertised as “lean,” “healthy,” or “smart”

Reference: Introduction to Food Science and Food Systems, pp. p. 159 Slide: 10-16

VI.

Home Freezing [ Time Allocation: 10 min.]

A. Overview 1. Freezing is one of the easiest, most convenient, and least timeconsuming methods to preserve food 2. Foods for the home freezer must have proper packaging materials a. Fruits and vegetables should not be frozen in containers with a capacity of more than one-half gallon b. Foods in larger containers freeze too slowly to result in a satisfactory product c. In general, packaging materials must have these characteristics: i. Moisture-vapor resistant ii. Durable and leak-proof iii. Not able to become brittle or crack at low temperatures iv. Resistant to oil, grease, and water v. Protect foods from absorption of off flavors or odors vi. Easy to seal vii. Easy to mark B. Rigid Containers 1. Rigid containers made of plastic or glass a. Suitable for all packs b. Especially good for liquid packs 2. Regular glass jars break easily at freezer temperatures C. Flexible Bags or Wrappings 1. Bags, sheets of materials resistant to moisture vapor, and heavyduty aluminum foil are suitable for freezing: a. Dry-packed vegetables b. Fruits c. Meats d. Fish e. Poultry 2. Bags can also be used for liquid packs 3. Laminated papers are suitable for: a. Dry-packed vegetables and fruits, meats, fish, and poultry b. Protective overwraps D. Freezer Pointers 1. The following pointers are for home freezing of foods: a. Freeze foods at 0 °F or lower

b. Freeze foods as soon as they are packaged and sealed c. Do not overload the freezer with unfrozen food d. Place packages in contact with refrigerated surfaces in the coldest part of the freezer e. Leave a space between packages so that air circulates freely E. Foods to Freeze for Quality 1. Fruit should be firm yet ripe—firm for texture and ripe for flavor 2. Vegetables should be young, tender, unwilted, and garden fresh F. Effect of Freezing on Spices and Seasonings 1. Freezing spices and seasonings can create undesirable effects a. Pepper, cloves, garlic, green pepper, imitation vanilla, and some herbs tend to become strong and bitter b. Onion and paprika change flavor during freezing c. Celery seasonings become stronger d. Curry may develop a musty off flavor e. Salt loses flavor and increases rancidity in items containing fat G. Freezer Management 1. A full freezer is most energy-efficient a. Refilling a freezer several times a year is most cost-efficient 2. Storage temperature must be maintained at 0 °F or lower a. At higher temperatures, foods lose quality much faster b. Use a freezer thermometer to frequently check the temperature Reference: Introduction to Food Science and Food Systems, pp. 159-162 Slides: 10-17 through 10-23

VII.

Summary [ Time Allocation: 5 min.]

• • • • • •

Freezing and refrigeration preserve foods not because they destroy microbes but because they slow or stop microbial growth Refrigeration temperatures range from 40 °F to 45 °F; frozen storage temperatures range from 32 °F to 0 °F During refrigerated storage, foods can experience the absorption of flavor and a loss of firmness, color, flavor, and sugar General freezing methods include still air, blast freezer, and fluidizedbed freezer To maintain quality, frozen foods must be packaged in airtight and liquid-tight strong and flexible containers Home freezing of foods follows the same general principles as commercial freezing

Reference: Introduction to Food Science and Food Systems, p. 162 Slides: 10-24 and 10-25

VIII. Assignment – Read Chapter 11 in Intro. to Food Science and Food Systems