Understanding and controlling changes in foods during processing and storage
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Industrial food processing has been a craft and an art, but is rapidly moving towards being a modern technology. One clear way to meet the enhanced sensory quality, safety, nutrition, health, economy, and novelty demanded of food products by consumers is by improving the operations of food processing. Improvement is related to the better prediction and control that follow quantitative description of the reactions, the chemical changes that occur during the processing of food materials – the rates of changes and the factors influencing the changes. This is the fundamental reason for writing this book at the present time, to indicate the wealth of knowledge becoming available on reactions in food processing, and the use of reaction technology to apply this knowledge in food processing. It is important that not only operations managers and technologists, but also development technologists and engineers, consider how reaction technology impacts on their present and future processes and products.

This book introduces the methods of reaction technology, setting its essence out simply and concisely, and illustrating how it has been and can be applied in industrial practice. It builds a framework for the application of reaction technology, and then uses this in straightforward, hopefully readily understandable examples with an industrial context. The numerical detail seeks to bring out a sense of magnitudes and rates appropriate to real systems, and to develop a feel for required processing precision matched both to the product quality outcomes and also to the necessities of the processing. It tries also to lead the reader to consider ways in which the examples can be extended into wider applications, with the intention that they will in turn point the way to more day-to-day use in food processing operations.

In some areas of food processing, reaction technology has been used for many years, because it has provided the reliability and safety that consumers demanded. Commercial sterilisation in canning was a very early pioneer; it has been joined by shelf-life prediction, and process control in the dairy industry. But these are largely isolated from the vast bulk of food processing operations, and even from each other by using different, and therefore potentially confusing, nomenclatures. There is a need to make reaction technology in food processing a coherent whole.

Many years ago after writing a small introductory book on unit operations in food processing, it was gratifying to see that it filled an apparent and substantial need and was very widely used across the world. Not only was it found applicable to the academic context for which it was intended, but it also found acceptance in a food industry that was becoming much more aware of how a structured and systematic technology could help in solving processing problems.

At the time, a parallel need could be discerned for looking into reactions of change in food constituents that were undergoing processing in the multitude of vessels, packages, and containers that are the reactors of the food industry. As with the unit operations, one of the great benefits of such an approach is to unify and thereby strengthen and reinforce the theory. It is then a short step to applications through borrowings and adaptations that assert themselves as obvious. Using such an approach in teaching and research over the years has further reinforced this. It demonstrated that students could appreciate and apply reaction technology directly to food processing. It was also continually amplified by the emergent literature. This literature has, after hesitant beginnings, come almost universally to work with and quote the standard methodology of chemical reaction engineering because that methodology is so direct and so applicable to the manifest needs of food processing.

It has always been a problem that, because of the innate complexity of so many food systems, full technological analysis can rapidly become too complicated for industrial application. This means that, to apply reaction technology in food processing, there must be careful selection of the important reactions, recognition of the levels of process accuracy necessary to achieve the specified product qualities, and use of modern information technology to analyse and control the process. Obviously, skill and knowledge are needed to design and operate a process using reaction technology, and this book introduces the knowledge and some of the skills in application required. It is not a textbook on reaction technology in food processing; that is left for the future.

The book sets out the general principles governing changes in the nature, the chemistry, of a food constituent and then extends this to include the dynamics of the reactions of the many chemical constituents of food raw materials and ingredients. It does this quantitatively because that is what process technology is all about. It demonstrates that many other important attributes, including microbiological safety and consumer acceptability, can very often be fitted comfortably into the general framework. It is illustrated by references from the publications of researchers, many of them chosen from the recent literature.

Where it seemed that there might be interest in background detail of theory, this has been touched on but in detached sections that can be skipped by those who are willing to accept results on trust.

Chapter 1 introduces the broad concepts relating the particular food situation to the general framework of reaction technology. There is more complexity than in most chemical technology, because of the composite nature of the raw material reactants. Adding this to the biological origins and the instability of food raw materials increases complications but creates no fundamental differences that cannot be incorporated or blended into the analysis. Included are not only typical food processing situations, but also extensions to new product and process design, shelf life and storage, process control, product quality and safety.

Chapter 2 shows how component concentrations in the foods are fitted to the rate equations, and basic concepts such as reaction order and activation energy are introduced. The rate equations lead to prediction of changes in concentrations of components, rates of changes and how these rates can be varied under the control of the industrial processor. The rates of change, their sensitivities to external influences such as the temperature and the times over which the process operates, determine the relative constitution and thus the properties of the final food product. Practical industrial food situations are used as illustrations.

Chapter 3 considers integration of the rate equations to predict the product outcomes. Analytical, numerical and graphical methods are described, and then applied to design and to control practical food processing situations. Because temperature conditions are often not uniform throughout the food, such as in a can or a loaf of bread, impacts of the differences on the reaction rates can be important. Important raw material variables extend beyond chemical concentrations, so the application of reaction technology to microbiological growth and death is also analysed.

Chapter 4 then extends the range from single reactions to multiple reactions, studying a number of reactants in series or in parallel, and to the relative rates of these. A number of reactions, selected as the critical ones for the product attributes and quality, are studied simultaneously and optimum processing conditions determined. Attributes such as the level of viable pathogenic or spoilage microorganisms, nutritional value, sensory assessments such as colour and flavour, and even general acceptability, can be included and assigned priorities to arrive at improved products. Examples of these are introduced and discussed.

Chapter 5 extends reaction technology from heat processing to other methods of processing using processing agents, and alternative energy sources such as irradiation, electrical and magnetic fields, and very high pressures. These are fitted into the general reaction technology framework. They can be used alone or in combinations, and can offer particular advantages since the total processing outcome is the sum of the separate changes, each fitting particular circumstances and contributing their own special features, which can all be analysed. The book ends with an analysis of several applications of the reaction technology approach, and then demonstrates something of the scope, the adaptability, and the success of the methods of reaction technology in food processing.

The book is in stages, so that those who are interested in the application of reaction technology can take it as far as they need. Those who need more detail for process development will hopefully be encouraged to take further steps. This can lead them into the massive body of published research results, and also the internal resources of data and knowledge that exist in many firms, but which have not been explored to their full capacity. The worked examples have been selected to illustrate applications as well as methods, and they make up an essential part of the text. Processing is practical and based on experimentation and measurement.

Mathematical analysis of the results can give the basis for prediction of effects on product quality of changes in process variables, and therefore the basis for both process design and control. Calculations can be quick and painless on modern hand calculators, or by using widely available computer software such as spreadsheets and graphics. From the predictions can come better and more consistent products, more efficient processes, and ideas that can contribute to the development of new products and processes. When approached systematically, it is perhaps surprising and certainly stimulating to see how much order can be applied through reaction technology to the apparently diverse food processing and preservation activities ranging across industries, institutions, restaurants, and homes.

The book is intended for industrial technologists working in process design, organisation and control, and for students of food science, technology and engineering. It is only an introduction, an appetiser. But it may serve to stimulate hunger to pick up and to make fuller use of what is understood and has been uncovered, and to give some direction towards what new knowledge needs to be found and developed for the future processing of better foods. It is hoped that it will also give technical managers an overall view of how the application of reaction technology in the future can lead to a “high tech” food industry.


Inevitably the contents of this book are built on the work of others. The names of all of them are far too numerous to mention, but some are singled out by inclusion in the references and examples. It is hoped that they have not been misrepresented or misquoted. That the literature exists is a huge resource for industry, and hopefully books such as this, suggesting the possibility of further uses for the published results, will help to make it even more useful. A great debt is owed to all who have worked and contributed to bring this knowledge to its present level.

The presentation used in this book was developed in undergraduate teaching in food and bio-processing in New Zealand and in Canada. Postgraduate students and industrial consultations in New Zealand and Britain enhanced it. It was crystallised by presentation in seminars to university teachers in Thailand, who found it useful in building their courses in food processing. Those participating have contributed to and enhanced the material, and for this we are grateful.

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Fundamentals of Food Reaction Technology. Copyright © 2003 Leatherhead Food International.
Web Edition published by NZIFST (Inc.)
NZIFST - The New Zealand Institute of Food Science & Technology