Continuous thermal processing of foods Pasteurization and UHT Sterilization

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Continuous Thermal Processing of FoodsPasteurization and UHT Sterilizationooo

Michael Lewis, BSc, MSc, PhDSenior Lecturer Department of Food Science and Technology The University of Reading Whiteknights, Reading United Kingdom

Neil Heppell, BSc, MSc, PhDSenior Lecturer School of Biological and Molecular Sciences Oxford Brookes University Headington, Oxford United Kingdom

AN ASPEN PUBLICATION Aspen Publishers, Inc. Gaithersburg, Maryland2000

The author has made every effort to ensure the accuracy of the information herein. However, appropriate information sources should be consulted, especially for new or unfamiliar procedures. It is the responsibility of every practitioner to evaluate the appropriateness of a particular opinion in the context of the actual clinical situations and with due considerations to new developments. The author, editors, and the publisher cannot be held responsible for any typographical or other errors found in this book. Aspen Publishers, Inc., is not affiliated with the American Society of Parenteral and Enteral Nutrition. The schematic drawing on the cover shows a typical continuous-flow thermal process with steam injection and expansion cooling. The drawing is adapted with permission from H. Burton, Ultra-High-Temperature Processing of Milk and Milk Products, p. 108, 1988.

Library of Congress Cataloging-in-Publication Data Lewis, MJ. (Michael John), 1949Continuous thermal processing of foods: pasteurization and UHT sterilization / Michael Lewis, Neil Heppell. p. cm. (Aspen food engineering series) Includes bibliographical references and index. ISBN 0-8342-1259-5 1. FoodEffect of heat on. 2. FoodPreservation. I. Heppell, NJ. II. Title. III. Food engineering series (Aspen Publishers) TP371 .L492000 664'.028dc21 00-040601 Copyright 2000 by Aspen Publishers, Inc. A Wolters Kluwer Company All rights reserved.

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Editorial Services: Kathy Litzenberg Library of Congress Catalog Card Number: 00-040601 ISBN: 0-8342-1259-5 Printed in the United States of America


My own book, Ultra-High-Temperature Processing of Milk and Milk Products, was published by Elsevier in 1988. A few years ago it became out of print, and I was asked to consider a revised second edition. After thought and discussion with others, it seemed to me that there was insufficient new material to justify a simple revision of the same book. There did, however, seem to be a need to extend the book to cover the ultrahigh-temperature (UHT) processing of more-viscous food products and of those containing particulates. I did not feel able to do this myself; by that time I had been away from active work for too long, and my direct experience did not include these newer applications. I suggested that Michael Lewis and Neil Heppell, both of whom I had known for some time, might be interested in writing such a book. They were prepared to take over where I left off, and Continuous Thermal Processing of Foods: Pasteurization and UHT Sterilization is the result of their work. In most respects this is a new and different book. Apart from an extension to viscous and particulate materials, they decided to include material on all continuous-flow heat treatment processes, which include pasteurization as well as UHT processes. Their approach has been that of chemical engineers, and much of the material specific to milk that I included has been omitted to accommodate material applicable to other products. However, some of the subjects covered in my book, particularly relating to UHT heat treatment systems and to aseptic filling methods, have changed little. Parts of my book dealing with these subjects have therefore been reused with little modification. I hope that their work will be well received and accepted as an important contribution to food-processing literature. I am pleased to have played some part in its inception and to have contributed to it. Harold Burton Reading, United Kingdom 2000


This book originated from a suggestion by the publisher for a revision of Harold Burton's book on ultrahigh-temperature (UHT) processing of milk, which was published in 1988 and which is now out of print. Harold dedicated this seminal book to all those who worked on UHT processing and aseptic filling at the National Institute for Research in Dairying (NIRD) between 1948 and 1985 and particularly those in the Process Engineering Group, of which he was head for much of the time. During that period his group did much of the fundamental work on understanding the safety and quality of UHT milk, and his name was known worldwide. Harold retired in 1985 and felt that he had been away from an active work and research environment for too long to undertake the task of revision, so he suggested to the publishers that Neil Heppell and I may wish to tackle it. Our relationship with Harold extends for more than twenty years. I was introduced to Harold by Reg Scott (the author of Cheesemaking Practice) shortly after my appointment as a lecturer in the Department of Food Science at University of Reading in 1973. Neil was a member of Harold's department and later registered for his PhD in the Department of Food Science. Others who followed a similar path were Sami Al-Roubaie, Geoffrey Andrews, Monika Schroder, and Paul Skudder, all of whom have contributed to the further understanding of continuous heat treatment. This helped to develop a good working relationship between NIRD and the university. Harold also worked with many other international experts on UHT during this period, some of whom spent periods of time studying at the NIRD. Meanwhile, the university obtained an APV Junior UHT plant in 1976, which has been used extensively for teaching, product development, and research since then. UHT activity at the university was summarized in a recent article (Lewis, M.J., 1995, UHT Processing, Research and Application, European Food and Drink Review', spring edition, 21-23, 25). Our first reaction to the suggestion for a revised edition was that there had not been sufficient further developments within ten years to warrant a direct updating of the book (I think this coincided with Harold's view). Therefore, we proposed a more ambitious project, extending the basic format of the book to cover continuous heat treatment in its wider aspects. Three major areas were identified to provide a wider coverage.

The first was to extend the range of food products covered beyond milk products alone. This is a simple aim to state, but one that in practice is much more difficult to achieve, as the bulk of the published research work on continuous heat treatment still relates to milk and milk-based products. This probably stems from milk being widely available, cheap, and extremely nutritious. The reason it is so nutritious is its chemical complexity, which in turn leads to its being both a very difficult and fascinating product to study. However, in contrast, the commercial reality is that there is now a much wider range of aseptic products available to the consumer, although the relevant technical information on such matters as formulations and processing conditions is not so easy to find in the public domain. There would appear to be plenty of scope for further experimental work on these products. This has been particularly noticeable in the chapters on sterilization, storage, and fouling and cleaning, which are predominantly milk-based. Although this book deals predominantly with milk and milkbased products, it also covers a wider range of products than any other currently on the market. The second aspect involved the realization that many of the products now processed are considerably more viscous than are milk and cream, and some of them contain discrete particles (deliberately added and not present as sediment). It was felt important to cover the heat treatment of more-viscous fluids, where streamline flow conditions are likely to prevail, as well as the thornier problem of heat-treating products containing particles, ideally ensuring uniform heating of the solid and liquid phases. It became necessary to cover the underlying principles and problems in more general terms without reference to specific products. The third important aspect was to extend the coverage to incorporate pasteurization and heat treatments designed to extend further the shelf life of pasteurized products. In fact, pasteurized products are more widespread than sterilized products in many countries. It was felt that this could be most effectively done by positioning the processes of pasteurization and sterilization next to each other to emphasize further their similarities and the differences. This was also felt to be the most appropriate place to discuss the heat