Pulsed Electric Fields Technology for the Food Industry (eBook)

PREFACE 6
Table of Contents 8
CONTRIBUTORS 13
PART I INTRODUCTION 15
CHAPTER 1 PULSED ELECTRIC FIELDS PROCESSING OF FOODS: AN OVERVIEW 16
1. INTRODUCTION 16
1.1. Historical Evolution and Chronological Developments in Pulsed Electric Field Processing 17
1.2. Present Status of Pulsed Electric Field Technology and Applications 20
2. FUNDAMENTAL ASPECTS OFPULSED ELECTRIC FIELD TREATMENT 22
2.1. System Components 23
2.1.1. Power Supply 23
2.1.2. Treatment Chamber 24
2.2. Effectiveness of Pulsed Electric Field Treatment 27
2.2.1. Technological Factors 27
2.2.2. Biological Factors 29
2.2.3. Media Factors 30
2.2.4. Inactivation Kinetics and Modeling 31
3. FUTURE ASPECTS AND ECONOMIC ANALYSIS OF PEF PROCESSING 32
3.1. Combination Studies 32
3.2. Drawbacks/Limitations 33
REFERENCES 34
CHAPTER 2 GENERATION AND APPLICATION OF HIGH INTENSITY PULSED ELECTRIC FIELDS 40
1. INTRODUCTION 40
2. ELECTRIC LOAD REQUIREMENTS 41
2.1. Specific Power Consumption 41
2.2. Average Power 43
2.3. Voltage Waveforms 45
2.4. Pulse Lengths and Repetition Rates 46
2.5. Conclusion 46
3. PULSED POWER SYSTEMS 47
3.1. General Remarks About Switches in Pulsed Power Generators 48
3.2. PEF Treatment Chambers 48
3.3. High-Power Sources 49
3.3.1. Basic Pulsed Power Circuits 50
3.3.1.1. Capacitive circuits 50
3.3.1.2. Inductive circuits 51
3.3.1.3. Ringing circuits 51
3.3.2. Circuits with Transformers or Other Voltage Multipliers 53
3.3.2.1. Circuits with pulse transformers 53
3.3.2.2. Circuits with storage transformers 54
3.3.2.3. Voltage multiplier I (MARX-generator) 55
3.3.2.4. Voltage multiplier II (GREINACHER cascade) 56
3.3.2.5. Current multiplier (XRAM-generator) 56
3.3.3 . Pulse Forming Networks 58
3.3.3.1. Pulse fanning lines 58
3.3.3.2. Pulse forming networks 60
3.3.4. Networks with Pulse Forming Switches 63
3.3.5. Concluding Remarks 64
3.4. Components of High Power Sources 65
3.4.1. High-Power Capacitors 65
3.4.2. Switches 67
3.4.2.1. Trigatrons 67
3.4.2.2. Ignitrons 69
3.4.2.3. Thyratrons and pseudospark switches 69
3.4.2.4. Thyristors, diodes, and IGCT switches 72
3.4.2.5. Concluding remarks 75
3.5. Low-Power Source 75
3.5.1. Basic Considerations 75
3.5.2. Typical Devices 76
APPENDIX A: DIFFERENTIAL EQUATION SYSTEM OF INHOMOGENEOUS PULSE FORMING NETWORKS 78
ACKNOWLEDGMENT 83
REFERENCES 84
CHAPTER 3 FUNDAMENTAL ASPECTS OF MICROBIAL MEMBRANE ELECTROPORATION 86
1. INTRODUCTION 86
2. ELECTROPORATION OF BIOMEMBRANES 87
3. ELECTROPORATION OF MICROORGANISMS OF INTEREST IN FOOD PRESERVATION 90
3.1. Electron Microscopy Examination 90
3.2. Leakage of Intracellular Material 91
3.3. Loss of Osmotic Response 91
3.4. Permeabilization to Nonpermeant Dyes 92
3.4.1. Effect of Process Parameters: Electric Field Strength, Treatment Time, and Specific Energy 92
3.4.2. Effect of Type of Microorganism 94
3.4.3. Effect of Product Characteristics 97
3.5. Occurrence of Sublethal Injury 99
4. CONCLUDING REMARKS 103
REFERENCES 104
PART II EFFECTS OF PULSED ELECTRIC FIELDS 108
CHAPTER 4 MICROBIAL INACTIVATION BY PULSED ELECTRIC FIELDS 109
1. INTRODUCTION 109
2. CRITICAL FACTORS DETERMINING MICROBIAL INACTIVATION BY PULSED ELECTRIC FIELDS 110
2.1. Processing Factors 111
2.1.1. Electric Field Strength 111
2.1.2. Pulse Shape 112
2.1.3. Pulse Width 113
2.1.4. Treatment Time 114
2.1.5. Frequency 114
2.1.6. Specific Energy 114
2.1.7. Temperature 115
2.2. Microbial Characteristics 115
2.2.1. Type of Microorganism 116
2.2.2. Cell Size and Shape 116
2.2.3. Culture Conditions 117
2.3. Treatment Medium Characteristics 117
2.3.1. Electrical Conductivity 118
2.3.2. pH 118
2.3.3. Water Activity 120
2.3.4. Composition of the Treatment Medium 120
3. MODELING MICROBIAL INACTIVATION BY PULSED ELECTRIC FIELDS 122
3.1. Collecting Data for Modeling Microbial Inactivation by PEF 122
3.1.1. Strain and Culture Conditions 123
3.1.2. PEF Treatment 123
3.1.3. Treatment Medium 124
3.1.4. Recovery Conditions 125
3.2. Primary Models for Describing Microbial Inactivation by Pulsed Electric Fields 125
3.3. Secondary Models for Describing Microbial Inactivation Pulsed Electric Fields 129
4. COMBINATION TREATMENTS 134
5. CONCLUSIONS 135
REFERENCES 136
CHAPTER 5 EFFECT OF PEF ON ENZYMES AND FOOD CONSTITUENTS 142
1. INTRODUCTION 142
2. EFFECT OF PEF ON ENZYME ACTIVITY 142
3. EFFECT OF PEF ON FOOD CONSTITUENTS 148
3.1. Proteins 149
3.2. Fats and Emulsions 150
3.3. Vitamins 153
3.4. Pigments 154
4. GENERATION OF NEW COMPOUNDS 154
5. QUALITY OF PEF-PROCESSED FOODS 155
5.1. Milk 155
5.2. Juices 156
5.3. Egg Products 158
5.4. Other Foods 159
6. CONCLUDING REMARKS 160
REFERENCES 160
CHAPTER 6 EXTRACTION OF INTERCELLULAR COMPONENTS BY PULSED ELECTRIC FIELDS 163
1. INTRODUCTION 163
2. THEORETICAL ASPECTS OF PEF INFLUENCE ON THE BIOLOGICAL MATERIALS 164
2.1. Disintegration Index and Characteristic Damage Time 164
2.2. Selective Concentration of the Electric Fields on Membranes in Biological Materials 165
2.3. MainMechanisms of Membrane and Cell Damage in External Electric Fields 166
2.3.1. Electroporation of Membrane 166
2.3.2. Joule Overheating of the Membrane Surface 167
2.3.3. Electroosmotic Transport Through the Membrane 168
2.3.4. Distinctness of the Cell Damage 168
2.4. PEF-Induced Structural Changes in a Cellular Tissue 169
2.4.1. Electrical Conductivity of PEF-Treated Tissues 169
2.4.2. Characteristic Damage Timeand Optimization Criteria 171
2.4.3. PEF-Induced Secondary Effects in a Cellular Tissue 173
3. APPLICATION OF PEF FOR SOLID/LIQUID EXPRESSION 175
3.1. Example of a Laboratory Device for the Combined Pressing and PEF Treatment 175
3.2. Mechanism of Solid/Liquid Expression from Biological Tissue Treated by PEF 176
3.3. Effect of PEF on the Behavior of Constant Pressure Expression from Food Plants 178
3.3.1. Consolidation Behavior 178
3.3.2. Solid/Liquid Expression with Intermediate PEF Treatment 181
3.3.2.1. Sugar beets 181
3.3.2.2. Apples 182
3.3.2.3. Carrots and spinach 182
3.4. Effect of PEF on the Behavior of Constant Rate Expression from Food Plants 182
3.5. Combination of PEF with a Moderate Heating 186
3.6. Pilot Studies of SolidlLiquid Expression Combined with PEF 189
4. EFFECT OF PEF-ENHANCING ON DIFFUSION OF WATER AND SOLUBLE SUBSTANCES FROM TISSUES 192
4.1. Models for PEF Treatment Enhanced Diffusion 193
4.2. Influence of PEF Protocol, Temperature, and Fragmentation of Particles on the Extraction Kinetics 195
REFERENCES 200
PART III APPLICATIONS AND EQUIPMENTS 204
CHAPTER 7 APPLICATIONS OF PULSEDELECTRIC FIELDS TECHNOLOGY FOR THE FOOD INDUSTRY 205
1. INTRODUCTION 205
2. PERMEABILIZATION OF CELL MEMBRANES 205
3. APPLICATIONS OF PEF TECHNOLOGY FOR THE FOOD INDUSTRY 207
3.1. Induction of Stress Response 207
3.2. Treatment of Plantor Animal Cellular Tissue 207
3.2.1. Juice Processing 207
3.2.2. PEF Treatment of Microalgae, Seaweed, and Other Aquatic Species 209
3.2.3. Plant Oil Extraction 210
3.2.4. Meat and Fish Treatment 211
3.2.5. Drying Enhancement 212
3.2.6. Sugar Processing 212
3.2.7. Energy Requirements for Tissue Disintegration 213
3.3. Microbial Decontamination 214
3.4. Wastewater Treatment 217
4. COST ANALYSIS 218
4.1. Fruit Mash Disintegration for Juice Winning 219
4.2. Cost Estimation for Beverage Pasteurization 220
5. PROBLEMS AND CHALLENGES 222
6. RESEARCH NEEDS, CONCLUSIONS, AND OUTLOOK 224
REFERENCES 225
CHAPTER 8 PULSED POWER SYSTEMS FOR APPLICATION OF PULSED ELECTRIC FIELDS IN THE FOOD INDUSTRY 230
1. INTRODUCTION 230
2. PEAK POWER REQUIREMENTS 230
3. CONTINUOUS POWER REQUIREMENTS 231
4. POWER SUPPLIES, SWITCHES, AND TREATMENT DEVICES 232
4.1. DC Power Supplies 234
4.2. Switches 234
4.3. Electrical Properties of Treatment Devices 235
4.3.1. Electrical Impedance 235
4.3.2. Comparison of Cell Resistance by Calculation and Measurement 236
4.4. Pulse Shapes 236
4.5. Measurement Under Pulsed Conditions 236
4.6. Partial Discharges, Electrical Breakdown, and Arcing 238
5. ELECTROCHEMICAL PROPERTIES OF PULSED POWER SYSTEMS 239
5.1. Electrochemical Reactions 239
5.2. Electrode Degradation by DC Offset 239
5.3. Metal Release Under Pulsed Conditions 241
5.4. More Sources of AC Components 242
6. PROCESS ASSESSMENT 243
6.1. Energy Input 243
6.2. Calorimetric Heat Output 244
REFERENCES 244
INDEX 246

"CHAPTER 1 PULSED ELECTRIC FIELDS PROCESSING OF FOODS: AN OVERVIEW (p. 3-4)

Gustavo v. Barbosa-Canovas and Bilge Altunakar

1. INTRODUCTION

The ever-increasing trend toward nutritionally qualified foods has challenged food technology to produce fresh-like foods by replacing thermal treatments with alternative methods of preservation. Thermal processing is a major technology that has been commonly used in the food industry to increase shelf life and maintain food safety with low processing costs (Knorr et al., 1994). To qualify as an alternative method, a new technology should have significant impact on quality while at the same time maintain the cost of technology within feasibility limits. In recent years, several technologies have been investigated that have the capability of inactivating microorganisms at lower temperatures than typically used in conventional heat treatments (Lado and Yousef, 2002).

Therefore, nonthermal methods correspond to the expectations for minimally processed foods of fresh quality, which have higher nutritional value because of color and flavor retention. Among all emerging nonthermal technologies, high intensity pulsed electric fields (PEF) is one of the most appealing technologies due to its short treatment times and reduced heating effects with respect to other technologies. High intensity pulse electric fields is highly appreciated as a nonthermal food preservation technology that involves the discharge of high voltage electric short pulses through the food product.

With the use of electric fields, PEF technology enables inactivation of vegetative cells of bacteria and yeasts in various foods. As bacterial spores are resistant to pulsed electric fields, applications of this technology mainly focus on food-borne pathogens and spoilage microorganisms, especially for acidic food products. In addition to the volumetric effect of PEF technology in controlling the microbiological safety of foods in a fast and homogenous manner, successful application provides extended shelf life without the use of heat to preserve the sensory and nutritional value of foods. PEF technology has the potential to economically and efficiently improve energy usage, besides the advantage of providing microbiologically safe and minimally processed foods.

Successful application of PEF technology suggests an alternative substitute for conventional thermal processing of liquid food products such as fruit juices, milk, and liquid egg (Mertens and Knorr, 1992; Bendicho et al., 2002a; Hodgins et al., 2002). This chapter gives an overview of the basics of pulsed electric field processing of foods within the food industry. Evolution of technology and certain factors involved are summarized with emphasis on a general review of PEF technology.

1.1. Historical Evolution and Chronological Developments in Pulsed ElectricField Processing

There are several ways to use an electrical source for food pasteurization, in the form of ohmic heating, microwave heating, and high intensity pulsed electric fields (HIPEF). Among these, ohmic heating is one of the earliest methods. Ohmic heating relies on the use of heat generated when an electric current passes through the food, and has already been approved for viscous and particulate products, especially for aseptic processing. Application of electric fields to preserve foods first appeared with the Electro-pure method for pasteurization of milk. In this early process, heat generated by an alternating electrical current (220-4200 V) was used as a method of thermal sterilization in which heat flowed through the milk."