Richard L. Earle is Professor Emeritus, Massey University, Palmerston North, New Zealand, where he was Head of Department of Process and Environmental Technology and Dean of the Faculty of Technology. Trained in chemical engineering and in operations research, he worked in the Meat Industry Research Institute of New Zealand. He then became Foundation Professor of Biotechnology at Massey University and was concerned with the processing of This communication (including any attachments) is intended for the use of the addressee only and may contain confidential, privileged or copyright material. It may not be relied upon or disclosed to any other person without the consent of the Royal Society of Chemistry (RSC). If you have received it in error, please contact us immediately. Any advice given by the RSC has been carefully formulated but is necessarily based on the information available, and the RSC cannot be held responsible for accuracy or completeness. In this respect, the RSC owes no duty of care and shall not be liable for any resulting damage or loss. The RSC acknowledges that a disclaimer cannot restrict liability at law for personal injury or death arising through a finding of negligence. VAT registration number GB 342 1764 71 Registered charity number 207890 4 biological materials across a wide range of products and industries including foods and pharmaceuticals. He wrote a pioneering textbook on Unit Operations in Food Processing, used throughout the world. He has taught reaction technology courses at undergraduate and graduate levels, and in industrial seminars in New Zealand, Canada, Thailand and Australia. He has been involved with the manufacturing industry, including the development of a pharmaceutical company using meat by-products in New Zealand, and has also authored or co-authored many papers and a number of books.

Fundamentals of Food Reaction Technology

By Mary Earle, Richard Earle

The Royal Society of Chemistry

Copyright © 2003 Leatherhead International Limited
All rights reserved.
ISBN: 978-1-904007-53-1

Contents

PREFACE,
1. IMPORTANT PROBLEMS IN FOOD PROCESSING, 1,
2. PRODUCT CHANGES DURING PROCESSING, 32,
3. PROCESSING OUTCOMES, 73,
4. ACHIEVING BETTER FOOD PRODUCTS, 109,
5. BROADENING THE NET, 144,
INDEX, 182,

CHAPTER 1

1. IMPORTANT PROBLEMS IN FOOD PROCESSING

1.1 Introduction

Food processing includes all the activities that control the nature of food between the agricultural and marine production and its final eating by the consumers. It includes everything from the controlled conditions in the transport and storage of whole fresh meat, fish, fruit and vegetables, to the complex processing producing food ingredients followed by manufacturing to produce the final consumer product. Before being eaten, biological materials from agriculture or fishing are transformed through processing into the finished foods the consumer wants. Food processing makes the food products more attractive, more satisfying, safer and easier to eat, and preserves them from deterioration. It includes building up desirable constituents and removing or reducing undesirable ones, encouraging enzymes to develop desirable flavours and textures and removing or inhibiting enzymes causing undesirable changes, growing microorganisms to create flavour and texture and destroying them to prevent harm to the consumer or decay of the food.

Food products are the outcomes of food processing, and it is important to identify the desirable product qualities and the undesirable and even unsafe product qualities. The products are the aim of food processing, and processing needs to be designed and controlled to give the product qualities identified and wanted by the consumers. Food processing is diverse, complex, and often carried out on a large industrial scale.

1.2 Changes During Food Processing

Processing causes changes in the food materials; some of the changes are shown in Table 1.1.

These changes can be measured, so their progress during processing can be followed and studied by the food technologist. The progress of processing can be measured in many ways, such as chemical analysis, physical measurements, counts of microorganisms, and colour, texture and flavour assessments by sensory panels. Changes can often be described in terms of the changing chemical composition, that is changes in the concentrations of the chemical components, but sometimes this is not possible and sensory, physical or microbiological measurements arc used to quantify the changes.

Measurement reveals continuing change with time during the process. As our knowledge extends over ever-wider ranges of foods and food processing, and our analytical skills increase, the measured changes arc increasingly found to be systematic and describable in quantitative terms. The quantitative data from change measurement can be fitted to mathematical equations and to physical models. The models can be tested and, if necessary, modified until they fit observations adequately for practical processing purposes. Once the models are sufficiently established, they can be used to predict changes in processing between and sometimes beyond the original processing conditions. The models can be employed industrially to guide the processing, to control its extent, and to design new processes and equipment. They can predict outcomes under different processing conditions, conditions that can be set before the processing is started and regulated until completion. Important processing variables include temperature, time, moisture level, pH and atmosphere, and different levels can be set to give the processing conditions.

The changes start when the process begins, and move on through the processing towards defined ends. The changes differ in their desirability between what are called customarily food processing and food preservation. Food processing, as seen traditionally, is about causing wanted changes in the food as it moves towards a finished product. These changes improve the food, adding to its value. For economic reasons, they often need to happen speedily. Food preservation aims to slow down undesirable changes, and conditions have to be organised so that the changes happen as little as possible. They are deleterious to the quality and value of the food. The changes are normally spontaneous, arising from the instability of the food, and the processing conditions are arranged to slow them down. Since they are both about change, its manipulation and its control, and since they can both be technologically described in the same way, it is convenient to think of the whole area as that of dynamic food processing.

In all dynamic food processing, the aim is always towards a defined product outcome. In food processing, the defined end is an optimum food product. In food preservation, the defined end is a point at which the food becomes significantly less edible or desirable, reaching a minimum acceptable quality. This is the point at which quality is measurably degraded and which the preservation process is designed to avoid reaching. Both involve changes that the technologist seeks to understand and keep under control. The changes take place under the scientific laws that govern reactions. They are influenced both by material qualities and by processing conditions, many of which are, or can be brought under the control of the processor. This book looks at the ways in which these changes occur, at quantitative descriptions of them in simple terms that can be used in practice, and at examples of industrial application.

Think break

Select two food-processing operations with which you are familiar.

* Identify all the changes that take place in the raw materials as they are moved through processing towards finished foods.

* Identify the individual chemical constituents so far as you can and the changes in these that occur.

* Consider the ways in which the changes are regulated and under control from the beginning to the end point in each stage of the process.

As an introduction, a number of important challenges involving the dynamics of change in food processing have been selected and will be outlined. Specific examples illustrate these challenges, focusing on food products and on food processing. They will show how, in particular industrial situations, the challenges have been studied using the methods of process reaction technology. In the later chapters there is more detailed discussion of how these methods can be applied generally and specifically to a range of food processes.

1.3 Food Products

Food products cover all edible products in the food system: industrial, foodservice and consumer products, primary produce, food ingredients, retail foods, and domestic foods. At the end, consumers determine the qualities expected of these products, but intermediate customers in the food system, such as food processors, food manufacturers and food retailers, very often set the working product specifications. Although these products may differ a great deal, their basic qualities can be grouped into composition, nutritional value, sensory, safety and health. In studying food processing, it is important firstly to identify the specific critical and important food qualities, called product attributes (or characteristics), required in each product, then to set the optimum values of the product attributes, so that food processing can be designed and controlled to attain the specified values for these specific attributes.

1.3.1 Consumer expectations

Consumer product expectations are built up from eating, or from publicity in the case of new and untried products. Consumer concerns include nutrition, food safety, shelf-life, as well as social and environmental aspects (2), but customers also very much want desirable sensory qualities and psychological benefits in the food. Expectations are becoming more specific all the time as consumers’ knowledge of food qualities increases. They want specific qualities and they want them to be true for all units of the products. For example, in the supermarkets, the customer wants today’s product to be true to the type and the quality bought last week or last month, and to a high degree of precision unless good reasons are produced for any change and such changes are acceptable.

Consumer expectations translate directly into buying specifications. When these product quality demands are combined with formal consumer requirements to list compositions and nutritional contents on packets, the food manufacturer has to pay attention, often minutely, to processing changes and to bring them under very precise control. The only real way to do this efficiently is to seek detail of, and manipulate, the process conditions as carefully as is currently possible.

1.3.2 Product attributes

A food product can be viewed at three levels – the consumer’s product concept, the total company product, and the company’s basic functional product (2). In setting the product aims for food processing, the consumer’s product expectations have to be converted into the company’s basic functional product, which is described by its physical, chemical, microbiological, sensory and nutritional attributes, as shown in Fig. 1.2.

General properties such as liking, use, convenience, safety, health, storage life, and consistency of quality and safety have to be converted into quantitative measures of specific product attributes with a required statistical framework. Sensory characteristics, such as appearance, aroma, flavour and texture, are developed into physical measurements, chemical constituents or sensory scores. The critical and important attributes, such as protein content, hardness, specific or general bacterial levels, acidity, solubility, and significant flavour(s), have to be identified for each product, and the required levels of these built into the final product specifications.

In studying food processing, it is important to identify:

• the critical and the important attributes of the final product

• levels of the critical and important attributes that are acceptable

• sensitivity of the product attributes to changes in processing conditions.

1.3.3 Product specifications

The industrial food processor combines ingredient product attributes into product buying specifications; today, these are very often set in conjunction with their industrial customers. The food manufacturer defines the product specifications for the final consumer products using the consumer knowledge from product development, but also with regard to regulatory and retailer requirements. Such groups as supermarket chains and multinational food manufacturers routinely use sophisticated product specifications. To produce food products with the required levels of attributes in the product specifications, the reactions producing these attributes need to be understood and controlled in the processing. This is illustrated in Fig. 1.3.

The sheer power of modern chemical analyses going down to parts per billion and the use of such tools as mass spectrometers, tristimulus colour meters, bacterial serotyping, and the continual emergence of new techniques, have provided the wherewithal for the buyer to discriminate almost infinitely. Additionally, if customer-buying specifications were not sufficiently demanding, governments and regulatory authorities are reacting to the substantial pressures imposed on them and exercising their powers ever more extensively. They have justifiably serious concerns for maintaining public health and safety. This is generating fresh stipulations all the time, for example on newly uncovered pathogens and including such processing-resistant entities as the prions, suspected of causing bovine spongiform encephalopathy (mad-cow disease) and thence perhaps variant Creutzfeldt-Jakob disease in people eating beef. In addition, regulations are being increasingly demanding on health statements and implications in advertising, for example for nutraceuticals and other foods claiming to be active for this or against that. All of these imply detail in food contents, which have to be properly certified by the processors and legally defended if needed. These requirements are demanded, not only in the food as it is initially placed on the shelves of supermarkets, but also increasingly until some nominated date thereafter.

Each process usually affects several specified attributes, which can be classified as critical, important and unimportant. For example, some of the attributes in orange juice are described in Example 1.1; there are important attributes, such as flavour and aroma, related to consumer acceptability, and a critical attribute, pathogenic organisms that could cause food poisoning.

Example 1.1: Important and critical attributes of orange juice

Fruit juices, such as orange juice, when newly extracted have the flavours and aromas of the original fruit. Many of the especially attractive features diminish gradually with time. The period of time the flavours and the aromas are retained depends on the particular fruit and ambient factors such as temperature and oxygen access. By using techniques such as chroma-tography, the gradual flavour losses can be monitored, and, by reference to sensory panels, quality thresholds can be set up. For example, the times needed under particular conditions to reach the level of flavour loss that is just detectable to trained panellists can be used as guides and references by the industry and retailers. Also, at the time of extraction, actual and potential off-flavours can arise, such as from citrus oils in the peel of the fruit.

More critically, pathogenic microorganisms can contaminate the juice. These pathogens constitute such a significant health hazard that, in some jurisdictions, notably the USA, legal regulations demand that the packed juice must be subjected to a process sufficient to reduce the numbers of the most resistant pathogens in the finished juice by a factor of five log. cycles, or else the food must be given a warning label that may be detrimental to marketing. This imposes a requirement on the processor to identify the most resistant pathogens in the product, and to ascertain the kinetics of their destruction. Any approved process can be used to ensure that the product meets the stipulations of the regulation with regard to pathogen reduction. This process may be pasteurisation, which is heat treatment, but it may also be one of a number of non-thermal processes, such as high pressure or irradiation.

Adapted from Mermelstein (3)

The attributes measurable in a food can be ranked as critical, where levels are mandatory (because of safety, regulations, contractual stipulations, company policies, strong consumer reaction), very important, where they are significant contributors to quality/value/market appeal, and then range down to unimportant. In processing, critical attribute levels must be maintained, very important ones should be maintained (subject to economic/plant criteria), whereas unimportant ones may not even be recorded (unless used as indicators of processing or product improvement).

Think break

Drink some UHT liquid milk and:

* Identify all the sensory attributes from first looking at the milk in the glass to the final swallowing.

Think break (contd)

* Group the sensory attributes into critical, important and unimportant.

* Choose the sensory product attributes to use for measuring the effect of changes in processing conditions.

* Decide what are the critical safety and nutritional attributes that must also be used to control the process.

1.3.4 Sensitivity of product attributes to processing conditions

A continuing problem in processing is assessing the sensitivity of critical and important attributes of the final product to changes in the controllable process variables such as temperature, atmosphere, moisture, catalysts, enzymes and, most importantly, time.

For example, bakers have seen batches of freshly baked bread and biscuits emerging from the oven with the colour of the crusts somewhere between overcooked and burned, and pondered hard whether they should all be rejected, or the darkest culled out, or maybe all of them let go to the market? In any event, it signals losses, even if only in consumer satisfaction. Appearances are important, and the surface on the top of the loaf or the biscuit is just so prominent. Obviously, temperatures have been too high somewhere in the oven or the loaves were spending too long there. Significant questions lie not only in the setting of the temperatures and time but also in the precision of controlling them. The complex relationships between time and temperatures determine the extent of the browning reactions that bring colour and flavour to the crust of the bread, but can also lead quickly to burning and charring. Would a drop in the oven temperatures (and if so how much) and/or shortening the times (and if so how much) allow the oven to produce paler and more consistent crust colour? But would this affect the texture of the loaf, making it doughy? Or would the shelf life of the loaf be reduced by growth of moulds?

These same broad questions permeate much of processing. ‘Trial and error’ experimentation will always bring solutions, but these experiments may be quite lengthy and expensive to work through, and they may still end up some distance from the best solution. When there are several simultaneous reactions proceeding in some process, there are trade-offs that have to be made amongst the processing conditions and they can almost always be made in a host of ways. Which are better, and is there a best? The sensitivities of the various critical and important attributes to processing conditions such as time and temperature need to be evaluated before selecting the optimum process conditions. Optimum process conditions for one attribute may be less than optimum for another, so compromises need to be made. In Example 1.2, this is discussed in regard to the pasteurisation of milk, one of the early examples of the use of reaction technology in processing, although such implications were only partially appreciated at that time.

Example 1.2: Pasteurisation of milk – choosing the processing conditions

For many years, and in most countries, cows’ milk for human consumption has been treated by pasteurisation, in which it is subjected to controlled heating. This is motivated almost totally for health reasons, and has had a demonstrable and beneficial effect on public health. Therefore, the criteria for the treatment were dominated by the conditions that provided the consumer with safety against organisms of concern, such as Mycobacterium tuberculosis and Coxiella burnettii. Regulations to demand a specific processing condition of temperature and time for liquid milk were imposed, in some countries virtually as soon as knowledge to do this was available.

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