Steele Understanding and Measuring the Shelf-Life of Food

1. Auflage 2004
ISBN: 978-1-85573-902-4
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 448 Seiten

Reihe: Woodhead Publishing Series in Food Science, Technology and Nutrition

The shelf-life of a product is critical in determining both its quality and profitability. This important collection reviews the key factors in determining shelf-life and how it can be measured.Part one examines the factors affecting shelf-life and spoilage, including individual chapters on the major types of food spoilage, the role of moisture and temperature, spoilage yeasts, the Maillard reaction and the factors underlying lipid oxidation. Part two addresses the best ways of measuring the shelf-life of foods, with chapters on modelling food spoilage, measuring and modelling glass transition, detecting spoilage yeasts, measuring lipid oxidation, the design and validation of shelf-life tests and the use of accelerated shelf-life tests.Understanding and measuring the shelf-life of food is an important reference for all those concerned with extending the shelf-life of food. - Reviews the key factors in determining shelf-life and how they can be measured - Examines the importance of the shelf-life of a product in determining its quality and profitability - Brings together the leading international experts in the field

Autoren/Hrsg.

Steele, R.

Inhaltsverzeichnis

1;Front Cover;1
2;Understanding and Measuring the Shelf-Life of Food;4
3;Copyright Page;5
4;Table of Contents;6
5;Contributor contact details;12
6;Part I: Factors affecting shelf-life and spoilage;16
6.1;Chaper 1. The major types of food spoilage: an overview;18
6.1.1;1.1 Introduction;18
6.1.2;1.2 Physical instability;19
6.1.3;1.3 Chemical spoilage (degradation);24
6.1.4;1.4 Microbial spoilage;26
6.1.5;1.5 Future trends;32
6.1.6;1.6 Sources of further information;33
6.1.7;1.7 References;34
6.2;Chaper 2. Shelf-life and moisture management;39
6.2.1;2.1 Introduction: moisture activity and shelf-life;39
6.2.2;2.2 Water activity and moisture management;40
6.2.3;2.3 The effects of moisture on the storage stability of food;44
6.2.4;2.4 How moisture management systems work: the case of meat jerky;47
6.2.5;2.5 Application of moisture management systems to food and other products;52
6.2.6;2.6 Future trends;55
6.2.7;2.7 Bibliography;56
6.3;Chaper 3. Temperature and food stability: analysis and control;57
6.3.1;3.1 Introduction: temperature and the shelf-life of food;57
6.3.2;3.2 Quantifying the effect of temperature on food;58
6.3.3;3.3 Shelf-life testing and indices;67
6.3.4;3.4 Shelf-life prediction and management: time–temperature relationships;68
6.3.5;3.5 Future trends;76
6.3.6;3.6 References;80
6.4;Chaper 4. Genetic and physiological factors affecting colour and firmness;84
6.4.1;4.1 Introduction;84
6.4.2;4.2 Physiology of firmness: fruits and vegetables;85
6.4.3;4.3 Methods of improving and maintaining firmness;87
6.4.4;4.4 Physiology of colour: fruits and vegetables;90
6.4.5;4.5 Methods of improving and maintaining colour;93
6.4.6;4.6 Future trends;97
6.4.7;4.7 Acknowledgements;100
6.4.8;4.8 References;100
6.5;Chaper 5. Spoilage yeasts;106
6.5.1;5.1 Introduction;106
6.5.2;5.2 Characteristics and classification of yeasts;107
6.5.3;5.3 Factors affecting the growth and survival of spoilage yeasts;112
6.5.4;5.4 Diversity and frequency of food spoilage yeasts;115
6.5.5;5.5 Factors affecting the inactivation of spoilage yeasts;118
6.5.6;5.6 Future trends: alternative technologies;121
6.5.7;5.7 Sources of further information;124
6.5.8;5.8 References;124
6.6;Chaper 6. Factors affecting the Maillard reaction;126
6.6.1;6.1 Introduction: the Maillard reaction (MR);126
6.6.2;6.2 Factors affecting the Maillard reaction;129
6.6.3;6.3 The Maillard reaction and spoilage: flavour deterioration;131
6.6.4;6.4 The Maillard reaction and spoilage: nutritional losses and browning;134
6.6.5;6.5 Improving shelf-life: antioxidative Maillard reactions;137
6.6.6;6.6 Improving shelf-life: the Maillard reaction and microbial spoilage;139
6.6.7;6.7 Conclusion;139
6.6.8;6.8 References;139
6.7;Chaper 7. Factors affecting lipid oxidation;143
6.7.1;7.1 Introduction: mechanisms of autoxidation;143
6.7.2;7.2 Factors influencing the rate of lipid oxidation;146
6.7.3;7.3 Methods of measuring oxidation in an oil or food;147
6.7.4;7.4 Monitoring changes in oxidation and the use of predictive methods;152
6.7.5;7.5 Future trends;155
6.7.6;7.6 Sources of further information and advice;155
6.7.7;7.7 References;155
6.8;Chaper 8. Lipolysis in lipid oxidation;157
6.8.1;8.1 Introduction;157
6.8.2;8.2 Lipolytic enzymes, lipids and food spoilage;158
6.8.3;8.3 Lipolysis in particular foods: dairy, meat and fish products;160
6.8.4;8.4 Lipolysis in particular foods: cereals and vegetables;165
6.8.5;8.5 Controlling lipolysis to improve shelf-life;168
6.8.6;8.6 Future trends;169
6.8.7;8.7 Sources of further information and advice;170
6.8.8;8.8 References;171
7;Part II: Measuring shelf-life and spoilage;178
7.1;Chaper 9. Ways of measuring shelf-life and spoilage;180
7.1.1;9.1 Introduction: understanding and estimating the shelf-life of food;180
7.1.2;9.2 Key factors influencing the shelf-life of food;182
7.1.3;9.3 Quality indices for testing the shelf-life of food;186
7.1.4;9.4 Conclusions and future trends;193
7.1.5;9.5 Sources of further information and advice;193
7.1.6;9.6 References;194
7.2;Chaper 10. Verification and validation of food spoilage models;199
7.2.1;10.1 Introduction: the modelling process;199
7.2.2;10.2 Validation and verification: definitions and use;201
7.2.3;10.3 Evaluation techniques and data transformation;204
7.2.4;10.4 Limitations of models;222
7.2.5;10.5 Future trends;226
7.2.6;10.6 Sources of further information and advice;227
7.2.7;10.7 References;227
7.3;Chaper 11. Measuring and modelling the glass transition temperature;233
7.3.1;11.1 Introduction;233
7.3.2;11.2 Measuring the glass transition temperature;234
7.3.3;11.3 Modelling the glass transition temperature;241
7.3.4;11.4 Conclusion and recommendations;244
7.3.5;11.5 Sources of further information and advice;244
7.3.6;11.6 References;245
7.4;Chaper 12. Detecting spoilage yeasts;248
7.4.1;12.1 Introduction: food spoilage yeasts;248
7.4.2;12.2 Detection and enumeration: viable and direct count techniques;250
7.4.3;12.3 Detection and enumeration: instrumental techniques;267
7.4.4;12.4 Methods of identifying and characterising foodborne yeasts;275
7.4.5;12.5 The use of microbiological indicators to monitor food quality and spoilage;282
7.4.6;12.6 Future trends;289
7.4.7;12.7 Sources of further information;290
7.4.8;12.8 Acknowledgements;290
7.4.9;12.9 References;290
7.5;Chaper 13. Measuring lipid oxidation;304
7.5.1;13.1 Introduction: lipid oxidation;304
7.5.2;13.2 Chemical methods of measuring lipid oxidation;305
7.5.3;13.3 Physical methods of measuring lipid oxidation;309
7.5.4;13.4 Chromatographic methods of measuring lipid oxidation;310
7.5.5;13.5 Measurement issues;318
7.5.6;13.6 Correlating analytical measurements with sensory evaluation;319
7.5.7;13.7 Measurement techniques and shelf-life improvement;323
7.5.8;13.8 Conclusions and future trends;323
7.5.9;13.9 Sources of further information;325
7.5.10;13.10 References;326
7.6;Chaper 14. Accelerated shelf-life tests;332
7.6.1;14.1 Introduction;332
7.6.2;14.2 Basic principles;332
7.6.3;14.3 Initial rate approach;333
7.6.4;14.4 Kinetic model approach;335
7.6.5;14.5 Problems in accelerated shelf-life tests;348
7.6.6;14.6 Future trends;350
7.6.7;14.7 References;352
7.7;Chaper 15. Shelf-life testing;355
7.7.1;15.1 Introduction;355
7.7.2;15.2 Assuring food safety: the HACCP system;357
7.7.3;15.3 Determining the shelf-life of food;358
7.7.4;15.4 Predicting the shelf-life of food;365
7.7.5;15.5 Conclusions;367
7.7.6;15.6 Sources of further information and advice;367
7.7.7;15.7 References;369
7.8;Chaper 16. Lipid oxidation and the shelf-life of muscle foods;372
7.8.1;16.1 Introduction;372
7.8.2;16.2 Lipid oxidation in vivo;373
7.8.3;16.3 Antioxidant defence systems;377
7.8.4;16.4 Lipid oxidation in muscle and muscle foods;382
7.8.5;16.5 Factors influencing lipid stability in meat and meat products;383
7.8.6;16.6 Cholesterol oxidation;389
7.8.7;16.7 Lipid oxidation and meat flavour, colour and drip loss;392
7.8.8;16.8 Meat packaging and shelf-life quality;396
7.8.9;16.9 Future developments;398
7.8.10;16.10 References;398
8;Index;411

Leseproben

2 Shelf-life and moisture management
R. Esse; A. Saari    Humidipak Inc., USA 2.1 Introduction: moisture activity and shelf-life
Many manufactured food products are adversely affected by moisture changes which directly impact their shelf-life and quality when they are consumed. These foods will lose desirable texture characteristics if allowed to lose or gain too much moisture. Brown sugar becomes hard and lumpy; raisins become hard. Ready-to-eat cereals lose their favored crisp textures if they gain moisture. Jerky becomes tough and dry. In addition, numerous other changes are affected by variations in moisture level. Some dry grain-based products can become rancid more rapidly through free radical oxidation at low humidities and thus become unacceptable. Labile nutrients such as vitamins and natural colors such as chlorophyll are oxidized more rapidly if stored at low moisture levels. On the other hand, if the moisture level is elevated, enzyme-mediated hydrolysis rates are increased significantly and the Maillard type of non-enzymatic browning is enhanced. Even small variations in storage temperatures will lead to localized high moisture conditions in an intermediate moisture food. These areas can be prime locations for microbial spoilage such as by loci of bacteria causing food infections or toxins of various types. Active moisture management systems should include humidity regulation. Packaging materials are used to control the ingress or egress of moisture vapor. Even if the packaging film has excellent moisture barrier properties, it cannot preserve the product in its optimal condition. The product, as produced, may have a moisture content slightly different from the optimum to achieve the longest shelf-life because of variability in the ingredients or the processing/ manufacturing system. A package may have minute leaks because of flex cracking of the material or flaws in the heat seal. The body of the package itself may have some measurable permeability to moisture vapor. These factors affect the changing moisture level of a food, significantly impacting the shelf-life and quality of a food product. The optimal approach is to have an active moisture regulation system that can react to and manage the changing conditions that take place over the life of a product. This chapter will help the reader understand such principles as water activity, moisture isotherm and moisture management/regulation systems. Understanding these principles is vital for development and distribution of products intended to be distributed nationally requiring a shelf-life of six months or more. They may be helpful also in the preparation of ‘fresh’ products which are distributed and consumed within a week or two. 2.2 Water activity and moisture management
To understand and apply a moisture management system, we must first have a basic understanding of water activity. This term, abbreviated to Aw, is a measurable value for all food products. It is a ratio and is expressed as a decimal fraction of 1.00 to two or three significant figures. Water activity (Aw) is defined as: w=Ps/Pw where Ps is the vapor pressure of a product or solution and Pw is the vapor pressure of pure water.* While the value is not precisely according to Raoult's Law, it is an adequate estimate for almost all situations. Further, since it is empirically measured, it reliably serves the purpose and is satisfactory for food product applications. Values of Aw range from 0.00 (absolutely dry) to 1.00 (pure water). Thus one obtains values such as 0.33 or 0.62 for water activities of specific products, a ready-to-eat cereal or dried fruit, respectively. This is a well-understood measurement by practitioners of food research. Instruments to directly measure Aw are readily available. Among the most reliable, moderately priced instruments are the dewpoint measuring meters which yield a numerical readout of the Aw for a sample within a few minutes. A careful experimenter can attain a repeatability of 0.002. When reporting results to a non-scientist, it may be conceptually preferable to convert the Aw value to relative humidity. We know the term relative humidity from weather reports and from being exposed to environments which can be expected to be comfortable, or uncomfortable. By definition: ?humidity?(RH)=Aw×100 For the purposes of this discussion, the experimental determination of Aw represents a degree of accuracy adequate and rigorous enough for the reader to better understand and identify applications that may require moisture management. Thus in the examples above, the food products can be said to have a 33% or 62% relative humidity, respectively, in the headspace of closed containers of the products. When the water vapor pressure of the food and the air surrounding it are equal, they are in equilibrium. This is not a static system, but a dynamic system where the loss of water molecules from the product equals the gain of water molecules from the environment. When this food product is exposed to an environment above or below this equilibrium point, the protective package and its barrier level will determine how much the food will be impacted. The second factor is the environment to which the package and its product are exposed. In drier climates the product may lose moisture and in more humid areas it will gain. If by chance it is exposed to a 33% relative humidity, no net moisture change will take place because the interior of the package is in equilibrium with its environment. Formulated or natural food products each have a unique Aw at which their texture is optimal. Changing the formulation can also change the Aw value, particularly if there is a change in a solute. For example, adding sucrose as a sweetener will reduce the Aw of a product. If a monosaccharide such as glucose or fructose is added, the Aw reduction will be almost double since a unit weight of glucose will add approximately 1.9 times as many molecules in solution as the same unit weight of sucrose. (See footnote on page 25.) If two or more products with different values of Aw are placed in a package, they will tend to converge to an intermediate Aw. Consequently, none of the components will be at their optimal moisture content. If it is necessary to combine such components in a single package such as a cookie with a fruit preserve filling, all of the components need to be reformulated to a common Aw, otherwise the cookie portion will seem ‘soggy’, lacking crispness, and the filling will be firm and hard to chew. It is a great challenge to produce a succulent fruit filling and a crisp cookie at an intermediate Aw. By selecting a mixture of sugars, flours, fats, emulsifiers, etc., a reasonably acceptable product with a long shelf stability (6–12 months) can be produced. However, such a product has a relatively narrow tolerance to changes in moisture or Aw. Natural products such as fruits, vegetables and cereal grains move through an Aw range as they grow from small green specimens to fully ripened edible products. Ripening often involves conversion of biopolymers such as starch to glucose or fructose as part of the process, thus reducing the Aw. Apples develop reduced Aw during ripening at a given total moisture content. During storage, the apples will consume some of the glucose to provide energy to sustain life. In time, the apples will become wrinkled and much less crisp as they lose moisture. Lettuce and other leafy vegetables wilt, losing turgidity and thereby the desirable crisp bite. This moisture loss can be slowed markedly by placing the food item in a more humid environment where it will achieve its longest shelf-life. It will be in acceptable flavor or eating quality for the longest period of time. In some products this can be days, in others it might be months. However, there is a downside to high humidity environments. Relatively small fluctuations in temperature may lead to condensation of water on the package or the product. This localized Aw of essentially 1.0 will encourage all microorganisms to grow. Cycling of temperature may tend to draw moisture out of a product. The rate of moisture loss is usually more rapid than take-up, so a product subjected to frequent temperature cycles will have a net loss of moisture. Since such environments are usually at a much lower humidity, the product suffers a net loss with each temperature cycle. It should also be noted that, contrary to perception, refrigerated spaces have a relatively low relative humidity, generally in the 30–40% RH range. The dewpoint of the air in a refrigerator is a function of the temperature of the cooling refrigeration coils in the chamber, be it a home refrigerator or a cold storage facility. All food products have an optimal Aw. In some cases, a slight change in the moisture content can make the product unacceptable. Examples might be freeze-dried mushrooms or powdered tomato base which each become unacceptable with only a slight increase in moisture. Beef jerky can have a considerable change in texture between an Aw of 0.74 and 0.76, a tolerance of less than 0.01. When this tolerance is very tight, it may mean that the product will need to be protected from the exposed environment with a high moisture barrier package. Other products have a high tolerance to fluctuation in their...