Sterilization of Food in Retort Pouches (eBook)

PREFACE 8
ACKNOWLEDGMENTS 10
CONTENTS 12
LIST OF FIGURES 16
LIST OF TABLES 22
LIST OF ABBREVIATIONS 24
1 THERMAL STERILIZATION OF FOOD 25
1.1. THERMAL STERILIZATION OF FOOD IN CANS 26
1.2. RETORT POUCHES (HISTORICAL REVIEW) 29
1.3. THERMAL STERILIZATION OF FOOD IN POUCHES 33
1.4. COMPUTATIONAL FLUID DYNAMICS AND THE FOOD INDUSTRY 35
1.5. OBJECTIVES 36
REFERENCES 37
2 HEAT TRANSFER PRINCIPLES 41
2.1. INTRODUCTION TO THERMAL STERILIZATION 41
2.2. HEAT TRANSFER 43
NOMENCLATURE 46
REFERENCES 46
3 PRINCIPLES OF THERMAL STERILIZATION 49
3.1. EFFECTS OF HEAT TREATMENT DURING STERILIZATION 49
3.2. EFFECT OF HEAT ON MICROBIAL POPULATION 51
3.3. EFFECT OF HEAT ON NUTRITIONAL PROPERTIES OF FOOD 54
3.4. REACTION KINETICS OF QUALITY CHANGES 54
NOMENCLATURE 55
REFERENCES 56
4 FUNDAMENTALS OF COMPUTATIONAL FLUID DYNAMICS 57
4.1. INTRODUCTION TO COMPUTATIONAL FLUID DYNAMICS 57
4.2. FINITE VOLUME METHOD AND PARTICULAR FEATURES OF PHOENICS 60
NOMENCLATURE 67
REFERENCES 68
5 THERMAL STERILIZATION OF FOOD IN CANS 69
5.1. INTRODUCTION TO THE THEORETICAL ANALYSIS OF THERMAL STERILIZATION OF FOOD IN CANS 69
5.2. SIMULATIONS OF HIGH- AND LOW-VISCOSITY LIQUID FOOD 69
6 THEORETICAL ANALYSIS OF THERMAL STERILIZATION OF FOOD IN 3- D POUCHES 117
6.1. THE PRINCIPLES OF POUCH MODELING 118
6.2. RESULTS OF SIMULATION 123
6.3. HEATING AND COOLING CYCLES 132
NOMENCLATURE 139
Subscripts 139
REFERENCES 139
7 POUCH PRODUCT QUALITY 141
7.1. BACTERIA INACTIVATION IN FOOD POUCHES DURING THERMAL STERILIZATION 141
7.2. RESULTS OF SIMULATION 145
7.3. DESTRUCTION OF VITAMINS IN FOOD POUCHES DURING THERMAL STERILIZATION 151
7.4. RESULTS OF SIMULATION 153
NOMENCLATURE 160
REFERENCES 160
8 EXPERIMENTAL MEASUREMENTS OF THERMAL STERILIZATION OF FOOD IN 3- D POUCHES 163
8.1. TEMPERATURE MEASUREMENTS IN POUCHES 163
8.2. ANALYSIS OF VITAMIN C (ASCORBIC ACID) DESTRUCTION 169
8.3. ENUMERATION OF SPORES AFTER HEAT TREATMENT 173
9 A NEW COMPUTATIONAL TECHNIQUE FOR THE ESTIMATION OF STERILIZATION TIME IN CANNED FOOD 181
9.1. INTRODUCTION 181
9.2. THEORETICAL APPROACH 182
APPENDIX A 193
APPENDIX B 197
APPENDIX C 211
APPENDIX D 213
APPENDIX E 217
APPENDIX F 221
APPENDIX G 223
INDEX 225

CHAPTER 2 HEAT TRANSFER PRINCIPLES (p. 17-18)

Food preservation remains to be one of the important food processing industries. Early approaches to food preservation applied the methods of preservation naturally available, such as sun drying, salting, and fermentation, which were used to provide food in periods when fresh foods were not available. As civilization developed, demand for large quantities of better quality processed food also increased. This led to the development of a large food preservation industry aimed at supplying food of high quality in an economical way. Thermal sterilization of foods is the most signi.cant part of this industry (Karel et al., 1975). Other methods of sterilization such as a pulsed electric .eld (Barbosa-Canovas et al., 1998, Barbosa-Canovas and Zhang, 2000, Jia et al., 1999, Martin et al., 1997, Qin et al., 1994, 1998, Sepulveda-Ahumada et al., 2000, Vega-Mercado et al., 1997, 1999, Zhang et al., 1995), ultrahigh hydrostatic pressure (Barbosa-Canovas et al., 1997a, Furukawa and Hayakawa, 2000, Paloua et al., 1999, Sancho et al., 1999), and ultraviolet (UV) treatment (Farid et al., 2000) have been widely studied. However, with the exception of high-pressure processing, these technologies have not yet reached commercialization stage.

2.1. INTRODUCTION TO THERMAL STERILIZATION

Two different methods of conventional thermal processing are known: aseptic processing, in which the food product is sterilized prior to packaging, and canning in which the product is packed and then sterilized (Barbosa-Canovas et al., 1997b). Food after being canned has to undergo thermal treatment to deactivate most organisms (i.e. sterilization). In 1981, the food industry in the United States alone processed more than 16.3 billion kg of food products in approximately 37 billion containers (Kumar et al., 1990).

Thermal sterilization is one of the most effective means of preserving a large part of our food supply. The objective of sterilization is to extend the shelf life of food products and make the food safe for human consumption by destroying harmful microorganisms. A sterilizer is a unit in which food is heated at high temperature and then held at that temperature for a period suf.cient to kill the microorganisms of concern from the foodproduct. A sterile product is one in which no viable microorganisms are present. A viable organism is one that is able to reproduce when exposed to conditions that are optimum for its growth. Temperature slightly higher than the maximum for bacterial growth results in the death of vegetative bacterial cells, whereas bacterial spores can survive at much higher temperatures. Since bacterial spores are far more heat resistant than vegetative cells, they are of primary concern in most sterilization processes. Saturated steam is the most commonly used and highly desirable heating medium for commercial sterilization of canned foods. Conventional canning consists of the following operations:

1. Preparing the food (cleaning, cutting, grading, blanching, etc.)
2. Filling the container
3. Sealing the container
4. Placing the container in a batch or continuous retort where it is heated for a time sufficient for commercial sterility
5. Cooling of the container, which is usually done using a cold shower

The still retort is the oldest type of equipment used for thermal processing. It is still used in large canning plants for metal- and glass-packed products. The sterilization method using a still retort consists of loading the containers, which are placed into baskets immediately after seaming and then into an appropriately designed iron vessel (retort), closing the vessel, and heating the containers with steam. A controller regulates the temperature, and the duration of heating is determined by the rate of heat transfer into the containers. Introduction of steam into the retort should be done with care since it is necessary to displace all of the air in the retort. The presence of air during thermal sterilization processing can result in under-processing since steam–air mixtures result in lower heat transfer rates (Karel et al., 1975).