Blackburn Food Spoilage Microorganisms

1. Auflage 2006
ISBN: 978-1-84569-141-7
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 736 Seiten

Reihe: Woodhead Publishing Series in Food Science, Technology and Nutrition

The control of microbiological spoilage requires an understanding of a number of factors including the knowledge of possible hazards, their likely occurrence in different products, their physiological properties and the availability and effectiveness of different preventative measures. Food spoilage microorganisms focuses on the control of microbial spoilage and provides an understanding necessary to do this.The first part of this essential new book looks at tools, techniques and methods for the detection and analysis of microbial food spoilage with chapters focussing on analytical methods, predictive modelling and stability and shelf life assessment. The second part tackles the management of microbial food spoilage with particular reference to some of the major food groups where the types of spoilage, the causative microorganisms and methods for control are considered by product type. The following three parts are then dedicated to yeasts, moulds and bacteria in turn, and look in more detail at the major organisms of significance for food spoilage. In each chapter the taxonomy, spoilage characteristics, growth, survival and death characteristics, methods for detection and control options are discussed.Food spoilage microorganisms takes an applied approach to the subject and is an indispensable guide both for the microbiologist and the non-specialist, particularly those whose role involves microbial quality in food processing operations. - Looks at tools, techniques and methods for the detection and analysis of microbial food spoilage - Discusses the management control of microbial food spoilage - Looks in detail at yeasts, moulds and bacteria

Autoren/Hrsg.

Blackburn, Clive de W

Leseproben

Introduction
C. de W. Blackburn, Unilever Colworth, UK Food spoilage: a matter of perspective
Microbial metabolism of organic matter is a naturally occurring process in the environment that is essential for the recycling of nutrients. These activities are generally referred to as biodegradation; however, when these organic materials are important for the well-being of humans, such as foods, then microbial metabolism is considered to be spoilage (see Chapters 1 and 14). Indeed, when microbial activities are harnessed for the benefit of humans, they are given constructive epithets such as fermentation and biotransformation. Food spoilage is therefore a social construct and can be defined as the process or change leading to a product becoming undesirable or unacceptable for human consumption. The manifestations of food spoilage are many and varied, and may be visual (e.g. discoloration, slime production, colony formation, breakdown of structure, blowing of container) or apparent by smell (e.g. off-odour) or taste (e.g. off-flavour, increase in acidity). Food spoilage may be caused by microbial, chemical or physical mechanisms. Although this compartmentalisation of the causes of food spoilage is convenient, there is really a continuum of causes and effects. However, by necessity this book is restricted to the microbial spoilage of foods with a focus on the major spoilage microorganisms and how they can be controlled. Microbial food spoilage and safety
Microbial food safety and spoilage are often separated; indeed, the concept of this book was to treat food spoilage microorganisms in a similar way to that of foodborne pathogens in the book of the same name (Blackburn & McClure, 2002). From the perspective of the microbiologist this separation is sometimes blurred or more complex, as exemplified by the potential for mycotoxin production by contaminating moulds and the shattering of glass containers caused by the build-up of carbon dioxide from contaminating yeasts. Perhaps more importantly in the eyes of the consumer and also the law, there is often no clear distinction. This has an associated impact on how the food industry perceives and manages food spoilage. Frequently the controls, preservation strategies and management procedures to ensure food safety are similar and overlap with those that control food spoilage. However, whereas safety is given priority, and rightly so, many food microbiologists spend much of their time ‘battling’ food spoilage microorganisms. An expensive business
Although exact figures of the total economic losses due to food spoilage are unknown it is clear that it constitutes an enormous financial burden. It has been estimated that a quarter of the world’s food supply is lost through microbial activity alone (Huis in’t Veld, 1996). Worldwide losses of grain and legumes have been estimated to be at least 10% of production and for non-grain staples, vegetables and fruits, the loss is believed to be as high as 50% (WHO, 1995). Food losses begin on the farm and continue throughout post-harvest storage, distribution, processing, wholesaling, retailing and use in the home and in catering (Roller, 1999). The competitive world economy means that no one can exist in isolation, and migration, overseas education and travel have resulted in tremendous demands for competitively priced food from different parts of the world (Merican, 1996). There is a two-way concern regarding safety and quality in importing and exporting countries that requires cooperation between developed and developing countries: the microbiological risks from products and/or ingredients from countries that have varying microbiological standards, and the dumping of substandard products in countries with insufficient monitoring systems (Merican, 1996). There are a number of trends and drivers from all parts of the food supply chain that present increasing challenges to control microbial spoilage for all those involved in food production and manufacture. From a consumer perspective there are paradoxical drivers for less heavily preserved/processed foods and organic foods, against improved quality, guaranteed safety, longer shelf-lives and competitive pricing. This consumer pressure is passed along the supply chain and it requires those involved in the food industry to reduce operating costs, e.g. by having longer run times between scheduled cleaning and disinfection procedures; global sourcing of ingredients; optimising/reducing thermal processes. This places enormous challenges on controlling microorganisms. The cost of microbiological mistakes range from having a high level of rework and/or product disposal to having to instigate a (trade or public) product recall. For example, in the USA between 1 October 1991 and 30 September 1992 there were 230 recalls, involving 569 foods and cosmetics, 25% of which were due to microbial contamination (Venugopal et al., 1996). The usual suspects
The range of spoilage microorganisms is wide. The increasing variety of consumer products together with the need to preserve flavour and texture through minimum processing means that the susceptibility to spoilage has increased, as has the diversity of spoilage species. Bacteria (Part V) are responsible for some of the most rapid and evident spoilage of proteinaceous foods such as meat, poultry, fish, shellfish, milk and some dairy products (Huis in’t Veld, 1996). Their range is huge and diverse, including the Gram-negative rods (e.g. Pseudomonas, Shewanella, Chapter 19), Gram-positive spore-formers (e.g. Bacillus, Clostridium, Chapter 21), lactic acid bacteria (Chapter 20) and other Gram-positive bacteria (Brochothrix, Micrococcus, Chapter 23) (Huis in’t Veld, 1996). In addition, the Enterobacteriaceae (Chapter 22) is a large group that as well as including spoilage bacteria also contains pathogens. Members of the group are often used as indicators of quality and safety. The growth of yeasts and moulds (Parts III and IV) is generally slower than that of bacteria, but the wide variety of ecological niches they can exploit, the ability to utilise a variety of substrates, and tolerance of more extreme conditions than (vegetative) bacteria makes them formidable spoilage agents (Huis in’t Veld, 1996). With regard to the yeasts, species of Zygosaccharomyces and related genera are usually the yeasts that colonise and spoil high sugar and high salt products (Chapter 10). Saccharomyces are best known for their positive contributions to food and beverage production, but they also can have deleterious effects including circumstances when the same species spoil the very commodities they produce (Chapter 11). Candida species make up one-quarter of all known yeasts and their heterogeneity means that they are responsible for the spoilage of a wide range of foods (Chapter 12). In contrast the yeasts within the Dekkera/Brettanomyces genera are primarily spoilers of beverages, particularly alcoholic beverages, and they are a major concern to the wine industry (Chapter 13). Although the yeast and mould forms of the fungi have been considered separately there is really a continuum, with some fungi exhibiting both single celled (yeast) and filamentous (mould) growth. However, the mould form has many specific characteristics that present specific problems with regards to food spoilage (Chapter 14). Although the range of moulds is immense there are a specific and rather limited number of genera and species that are spoilage hazards for each kind of food (Filtenborg et al., 1996). The Zygomycetes, popularly known as the ‘pin moulds’ are often seen as rapid growers following a ‘hit and run’ strategy for the foods that they spoil (Chapter 15). The Penicillia (Chapter 16) and Aspergilli (Chapter 17) are common spoilage moulds with the latter generally growing more rapidly and at higher temperatures or lower water activities than the former. Other types of moulds are significant in food spoilage (Chapter 18), but many moulds may be present on, or isolated from, foods in which they never or rarely cause spoilage (Chapter 18). The need to compartmentalise is inherent in microbial classification and taxonomy, but the given name is often of only transient significance. New approaches in taxonomy utilising phylogenetic criteria (e.g. 16S rRNA and DNA sequence comparisons), while not significantly affecting foodborne pathogens, have had an impact on some food spoilage bacteria (Jay, 2003). These methods have been applied to some long-established genera of bacteria of importance in foods including: Bacillus, Clostridium, Flavobacterium, Micrococcus, Pseudomonas, Staphylococcus and Xanthomonas. The use of these molecular genetic methods allows the construction of bacterial taxonomy along phylogenetic rather than phenotypic lines (Jay, 2003). Molecular techniques have also brought greater understanding of the fungal genome and with it subsequent changes to fungal taxonomy (Chapter 17). Many species have a history of being established, dis-established, re-established or transferred to different genera, which has caused much confusion to researchers and industry professionals (Chapter 11). New...