Food sterilization has been well studied in a large number of textbooks. This book is not about the science of sterilization or food safety but rather about the important interaction between fluid mechanics, heat transfer, and microbial inactivation. Such interaction is complex and if ignored would lead to incorrect information not only on food sterility but also on food quality.
The book is written by engineers for both food engineers and scientists. However, it may also be of interest to those working in computational fluid dynamics CFD. It presents an elementary treatment of the principles of heat transfer during thermal sterilization, and it contains sufficient material presented at a high level of mathematics. A background in the solution of ordinary and partial differential equations is helpful for proper understanding of the main chapters of this book.
However, we have avoided going into a detailed numerical analysis of the finite volume method FVM of solutions used to solve the sets of equations. Some familiarity with fluid dynamics and heat transfer will also be helpful but not essential. In this book, conduction and convective heat transfer is treated such that the reader is offered the insight that is gained from analytical solutions as well as the important tools of numerical analysis, which must be used in practice.
Analysis of free convection is used to present a physical picture of the convection process. The first three chapters present a brief historical review of thermal sterilization of food, funda- mentals of heat transfer, and principles of thermal sterilization, in order to acquaint the reader with those materials to establish more firmly the important analogies between heat, mass, and momentum transfer. These chapters provide the reader with a good balance between fundamentals and applica- tions; they provide adequate background information to the point.
The computer is now the preferred tool for the solution of many heat transfer problems. Personal computers with powerful software offer the engineer the power for the solutions of most problems. Chapter 4 deals with numerical modeling and fundamentals of CFD and is one of the highlights in this book. The subject of sterilization of food in cans has been well studied both experimentally and theoretically, but very limited work has been undertaken to study the sterilization of food in pouches.
In this book, natural convection heating of viscous liquid foods of different types broccoli-cheddar soup, carrot-orange soup, and beef-vegetable soup in a uniformly heated 3-D pouch is presented in Chapter 6 for the first time in the literature.
The slowest heating zone SHZ and its migration for each case of cans and pouches are presented and analyzed. The results of a simulation performed for the same pouch, but based on conduction heating, are also presented to illustrate the importance of free convective heat transfer in sterilization.
The effect of retort come-up time the time required for the temperature of the retort to reach a selected constant processing temperature after steam is turned on is also studied in one of the simulations presented in Chapter 6. Thermal sterilization of liquid food always results in important biochemical changes such as bacteria inactivation and nutrient concentration changes.
The concentration distribution of live bacteria and vitamins C ascorbic acid , B1 thiamine , and B2 riboflavin in a pouch filled with different liquid food materials during thermal sterilization is presented in Chapters 7 and 8.
In these simulations, the governing equations for continuity, momentum, and energy are solved numerically together with the equations defining the concentration of live bacteria and vitamins. Although the main theme of the book is to present a theoretical analysis of the sterilization process and nutrient quality, some experimental validation was necessary. However, this was merely to validate the theoretical prediction and may not be considered as a thorough analysis of the sterilization process, which is the subject of other published textbooks on sterilization.
In Chapter 9, experimental measurements are presented to validate the theoretically calculated temperature distribution in the pouch. The predicted temperatures are compared with those measured at different locations in the pouch and subsequently analyzed. The analysis of sterilization of liquid food in pouches and cans is complicated by the important effect of free convective heat transfer, which requires the numerical solution of the Navier Stokes equations as presented in Chapters 5 to 8.
This numerical solution is time-consuming and challenging. Such facilities and expertise may not be always available to those working in the food industry. Chapter 10 presents a simplified analysis of the thermal sterilization in vertical and horizontal cans, utilizing the vast information available from the detailed simulations. An effective thermal conductivity is used to account for convection similar to the approach usually used to describe free convection heat transfer in cavities.
The analysis provides a quick and simple prediction for sterilization time. This text presents for the first time the analysis of sterilization of liquid foods in 3-D pouches.
The emphasis is to develop numerical techniques that can lead to a computer solution for such realistic engineering problems. The book is useful for engineers and food scientists where heat transfer is one of the basic disciplines. However, the book is more suitable as a text for postgraduate students and researchers; it provides a reference to the analysis of sterilization of cans and pouches, using CFD.
We would also like to thank Professors Dong Chen and Gordon Mallinson for their valuable discussions and comments. Special thanks go to Professor Gustavo V. Finally, we would like to thank our families for being patient and very supportive during the writing of this book and the many years of work prior to that. Thermal Sterilization of Food: Historical Review 1 1. Thermal Sterilization of Food in Cans 2 1.
Retort Pouches Historical Review 5 1. Benefits of the Pouch 5 1. Steps to Regulatory Acceptance 7 1. Thermal Sterilization of Food in Pouches 9 1. Computational Fluid Dynamics and the Food Industry 11 1. Objectives 12 References 13 2. Heat Transfer Principles 17 2.
Introduction to Thermal Sterilization 17 2. Heat Transfer 19 2. Unsteady-State Heat Conduction 19 2. Convection Boundary Conditions 20 2. Free Convection 21 Nomenclature 22 Subscripts 22 References 22 3. Principles of Thermal Sterilization 25 3.
Effects of Heat Treatment During Sterilization 25 3. Heat Penetration 25 3. Heat Resistance of Microorganisms 26 3. Effect of Heat on Microbial Population 27 3. Effect of Heat on Nutritional Properties of Food 30 3. Fundamentals of Computational Fluid Dynamics 33 4. Introduction to Computational Fluid Dynamics 33 4. Solution of the Problem Processor 35 4. Analysis of the Results Postprocessor 35 4.
The Conservation Equations 38 4. Conservation of Mass Continuity 38 4. Conservation of General Intensive Properties 39 4. Conservation of Momentum 41 4. The Transport Equations and Related Physics 42 4.
Equation of State 42 4. Constitutive Equation 43 4. Body Force 43 4. Turbulence 43 4. Thermal Sterilization of Food in Cans 45 5. Basic Model Equations and Solution Procedure 45 5. Computational Grid 46 5. Bond strength of the various laminate layers is assessed by physically tearing the layers apart. Burst strength of the pouch is measured by filling it and then subjecting it to a specific force.
Oxygen permeability and water transmission rates are measured on bag samples before and after processing. Retort technology can be applied to process ready meals, sauces, marinades, vegetables curry, soups, and rice. Advantages of using retortable flexible containers No refrigeration or freezing required Packaging Material Foods can be sterilized in rigid containers like glass, metal cans and plastic or flexible retort pouches.
Cans and glass jars Metal cans and glass jars are widely used for retort processes, because of their high mechanical strength, thermal stability, resistance to pressure, and excellent barrier properties. Processing Using autoclaves, steam, steam spray,water spray, etc The quality assurance for retort pouches is usually assessed according to the following tests: 1.
Commercial Application of Retort Technology Retort technology can be applied to process ready meals, sauces, marinades, vegetables curry, soups, and rice. Post Views: 12, During this step, the operator is required to make operator entries: at least one check and entry of the MIG reading entry, one for the Chart reading, and one for the Bleeder Valve check.
All operator entries must be made for the step to be completed. During the Cook Step of a saturated steam process, the batch would be declared an Uncleared Deviation if the operator made an entry that indicated a bleeder valve failure after making a visual check. During the Cook Step of a saturated steam process, the batch would be declared an Uncleared Deviation if water is detected at a height sufficient to reach the bottom of the basket.
This step begins the cooling process. The cooling water enters the retort as overriding pressure control is initiated. In the initial phase of this step, steam is collapsed by the cooling water, which is displaced by large quantities of air. As the vessel fills, pressure will build as the air is compressed by the rising water level.
The BPR valve is used to relieve excess pressure while the air valve is used to make up pressure. When the water level, defined in the recipe, is reached normally at the top of the basket , the step ends. This step continues the retort cooling process. Cooling water continues to flow into the Process Vessel and flows out through the drain valve, which controls the level. Control to the recipe pressure setpoint is maintained using the Pressure Relief valve and Air Pressure Makeup valve with a dead-band of.
When the pressure cool time is completed and the recipe temperature is met, the step ends. Control is removed from the Pressure Relief valve, releasing pressure by opening the vent valve note: pressure may be steadily released using ramp control employed in a second Pressure Cool step. When the atmospheric cool time is completed, and an established temperature setpoint in the Process Vessel is achieved, the step ends.
This step drains the water from the retort. The drain is opened the water gravity-drains from the retort. When the level condition is met, the step ends.
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