Food Preservation by Pulsed Electric Fields

From Research to Application

H.L.M. Lelieveld, S Notermans, S W H De Haan, H. L. M. Lelieveld

• Publisher: Woodhead Publishing
• Year: 2007
• Print ISBN: 9781845690588
• eBook ISBN: 9781845693831
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Pulsed electric field (PEF) food processing is a novel, non-thermal preservation method that has the potential to produce foods with excellent sensory and nutritional quality and shelf-life. This important book reviews the current status of the technology, from research into product safety and technology development to issues associated with its commercial implementation.Introductory chapters provide an overview of the process and its history. Part one then discusses the technology of PEF food preservation, with chapters on circuitry and pulse shapes, chamber design and technical and safety requirements. The second part of the book focuses on important product safety and quality issues such as probable mechanisms of microbial inactivation by PEF, adaptation potential of microorganisms treated by this method, toxicological aspects, the impact on food enzymes and shelf life. Chapters in the final part of the book cover topics relating to the commercialisation of the technology, including current and future applications, pitfalls, economic issues and scaling up, and public and regulatory acceptance.Food preservation by pulsed electric fields is a standard reference for all those involved in research into PEF food processing and its commercialisation. - Reviews the current status of PEF technology with an overview of the process and its history - Discusses the technology involved in PEF food preservation - Focuses on important product safety and quality issues such as the impact on food enzymes and shelf life

1

Preservation of food by pulsed electric fields: An introduction

S. Notermans Foundation Food Micro and Innovation, The Netherlands

1.1 The need to preserve food

1.1.1 Historical aspects

The need to preserve food has a long history. Problems with deterioration must have been a continuous preoccupation of early humans, once they began their hunting and food-gathering activities, and domestic production of food animals and crops. Although the exact timing is uncertain, organised food production probably started between 18 300 and 17 000 years ago, when barley production is said to have flourished in the Egyptian Nile Valley (Wendorf et al., 1979). During that time, there was a need to preserve the grain and keeping it in a dry condition was an obvious precaution. Attempts to preserve other foods were based mainly on experience gained in linking the spoilage of the food with the manner in which it had been prepared and stored. Increasingly, it became clear that food could only be maintained in an acceptable condition if the product was kept dry and away from contact with air. Some foods were treated with honey and later with olive oil (Toussaint-Samat, 1992). This led to the development of additional preservative measures, such as heating and salting. Once the preservative capability of salt was discovered, the value of this substance increased, since it was not available in sufficient quantity to meet the demand. According to Toussaint-Samat (1992), the large amount of salt in the Dead Sea was one of the reasons for the interest of the Romans in Palestine.

Over many millennia, mankind has also learned to select edible plant and animal species, and to produce, harvest and prepare them in a safe manner for food purposes. This was done mostly on the basis of trial and error from long experience. Many of the lessons learned, especially those relating to adverse effects on human health, are reflected in various religious taboos, which include a ban on eating specific items, such as pork, in the Jewish and Muslim religions (Tannahill, 1973). Other taboos showed a more general appreciation of food hygiene. In India, for example, religious laws prohibited the consumption of certain ‘unclean’ foods, such as meat cut with a sword, or sniffed by a dog or cat, and meat obtained from carnivorous animals (Tannahill, 1973). Most of these food safety requirements were established thousands of years ago when religious laws were likely to have been the only ones in existence. The introduction of control measures in civil law was of a much later date. A more recent example of discovering that preservation was an effective tool in preventing disease was in the time of the cholera and plague epidemics. It was noted that beer-drinkers did not fall ill and the brewing and drinking of beer became very popular. The main reason for this was that beer, due to the production process used, is a well-preserved product and does not contain any pathogenic organisms.

Because the underlying causes of food spoilage and food-borne illness were unknown, spoilage and poisoning were recurrent problems. However, the situation changed after 1795, when the French government, driven by war, offered a substantial reward for anyone developing a new method of preserving food. It was Nicolas Appert, a Parisian confectioner, who accepted the challenge and developed a wide-mouth glass bottle that was filled with food, before being corked and heated in boiling water for about six hours. In 1810, Durand in England patented the use of tin cans for thermal processing of foods, but neither Appert nor Durand understood why thermally processed foods did not spoil (Hartman, 1997), despite the fact that in 1677 van Leeuwenhoek had discovered ‘his little heat-sensitive animalcules’ (Dobell, 1960).

It was Louis Pasteur who provided the scientific basis for heat preservation in the period 1854–1864. During that time, he showed that certain bacteria were either associated with food spoilage or caused specific diseases. Based on Pasteur’s findings, commercial heat treatment of wine was first introduced in 1867, to destroy any undesirable micro-organisms, and the process was described as ‘pasteurisation’. Another important development occurred in Germany, when Robert Koch introduced a method of growing micro-organisms in pure culture and, with colleagues, first isolated the cholera vibrio in 1884, during a worldwide pandemic (Chung et al., 1995). Over the next 100 years or more, laboratory isolation and study of pure cultures of microbes remained among the predominant activities of food microbiologists (Hartman, 1997).

Following the discovery of micro-organisms and recognition of their pathogenic potential towards the end of the 19th century, food preservation developed on more scientific lines. Preventing spoilage and keeping food safe were no longer the only reasons for preservation. Increasingly, preservation has become important in maintaining product quality and especially food flavour. Clear examples are the production of sauerkraut, kimchi, several types of ham and sausage and many dairy products. Nevertheless, preventing spoilage and ensuring product safety are still the main objectives of food preservation. Despite this, EU Council Directive No. 95/2 EC describes preservatives as ‘substances which prolong the shelf-life of foodstuffs by protecting them against deterioration caused by micro-organisms’.

1.1.2 Quality loss and food safety

Loss of quality in foods is caused by a wide range of reactions. These include processes that are predominantly physiological (respiration of fruit and vegetables), physical (changes in texture following freezing), chemical (oxidation of fatty acids, loss of colour), enzymatic (enzymatic browning), biological (damage by insects) or microbiological (food spoilage). Changes in organoleptic characteristics, freshness and suitability for human consumption must also be taken into account. Of all the adverse reactions in foods that affect product quality, the microbiological ones are the most severe. It has been estimated that, currently, about 25% of the world’s food supply is lost from microbial spoilage (Huis in’t Veld, 1996). The available means of combating the deleterious effects of micro-organisms are to prevent contamination, kill the organisms in situ or slow their growth. Therefore, preservation processes are increasingly being integrated into the food-production chain. Such an approach allows the use of mild preservation treatments, thus avoiding unnecessary quality loss caused by the treatment itself.

Whilst most preservation techniques aim to control all forms of quality loss that can occur, the overriding priority is always to minimise the occurrence and growth of micro-organisms, particularly those that can cause food poisoning or food-borne infections (Russell and Gould, 2003). The main reason is the ‘high’ levels of reported food-borne illness (see, for example, Mead et al., 1999), which, incidentally, has stimulated an interest in the use of preservative treatments (Rombouts et al., 2003). Preservatives may contribute to the control of food-bo...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributor contact details
• Preface
• 1: Preservation of food by pulsed electric fields: An introduction
• 2: History of pulsed electric field treatment
• Part I: Technology
• Part II: Product safety and quality
• Part III: Applications
• Index