Food Spoilage Microorganisms

Clive de W Blackburn

• Publisher: Woodhead Publishing
• Year: 2006
• ISBN:
  9781845691417
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

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

Part I

Detection and analysis of food spoilage

1

Quantitative detection and identification methods for microbial spoilage

D.I. Ellis; R. Goodacre University of Manchester, UK

1.1 Introduction

Microbial metabolism of dead or decaying matter is a naturally occurring process in the environment, and is essential for the recycling of nutrients. Microbial metabolism of foodstuffs, however, that leaves them either unfit or unacceptable for human consumption is commonly termed microbial spoilage. It is to the obvious benefit of producers and processors of food to halt or delay this process for as long as possible. In the modern and highly automated food processing industry the ability to detect the onset or source of microbial spoilage is particularly advantageous as spoilage can lead to large-scale losses in economic terms and outbreaks of foodborne illness.

The microbial spoilage of foods has always been problematic and has been known for centuries, for example in the brewing industry where lactic acid bacteria can spoil beer by causing turbidity, acidity and unfavourable odours (Takahashi et al., 2000; Sakamoto and Konings, 2003; Suzuki et al., 2004). Indeed, as an ideal source of nutrients for bacteria and fungi all foodstuffs can be affected, including dairy products (Bleve et al., 2003; Gunasekera et al., 2003), eggs (Erickson and Jenkins, 1992; Deeming, 1996), fruit (Leverentz et al., 2003), vegetables (Jacxsens et al., 2001; Allende et al., 2004), juices (Casey and Dobson, 2004; Chang and Kang, 2004), fish (Gram and Dalgaard, 2002; Tryfinopoulou et al., 2002; Skjerdal et al., 2004), meat (Lebert et al., 2000; Jay et al., 2003) and poultry (Kalinowski and Tompkin, 1999; Ellis and Goodacre, 2001; Hinton et al., 2004). Therefore, as the potential scope of this particular area of food microbiology could take up a book in itself, this chapter will concentrate on microbial spoilage in meat, and in particular poultry, which is also an area in which the authors have practical experience.

In terms of food safety and foodborne illness, muscle foods (which include meat and poultry), as well as being a widely consumed and relatively inexpensive protein source, are an important foodstuff with both worldwide economic and public health significance (Altekruse et al., 1999; Mead et al., 1999; Vellinga and Van Loock, 2002). The health risks associated with the consumption of spoiled or contaminated meats, for example, are considerable and include debilitating and potentially lethal microbial diseases such as salmonellosis (Zhang-Barber et al., 1999; Schlundt, 2001; White et al., 2001), campylobacteriosis (Chan et al., 2001; Frost, 2001; Newell et al., 2001), and haemorrhagic colitis (Tarr et al., 1997; Cassin et al., 1998; Tuttle et al., 1999). Moreover, the global magnitude of the production, processing and retail industries also makes muscle foods extremely important in economic terms. Therefore, any advancement in the quantitative detection and identification methods for the microbiological contamination/spoilage of meats and poultry would be beneficial, in terms of both the health risks associated with food contamination and any reduction in large-scale losses due to bacterial spoilage. However, it must be stressed that any advancement in detection methods should ideally be concomitant with increased control of the microbial hazards at source if the health risks are to be reduced.

1.2 Microbial spoilage of meat and poultry

Meat and poultry are generally described as spoiled when undesirable changes have made them unacceptable to the consumer (Jackson et al., 1997). These organoleptic changes can include purely visible changes (such as discoloured meat), malodours or slime formation. It could be any one or combination of these changes, or indeed any other characteristic that makes the food undesirable for human consumption, that leads to the foodstuff being described as ‘spoiled’ (Jay, 1996; Jackson et al., 1997). It has been established that endogenous post-mortem enzymatic activity within muscle tissue, such as the activity of Ca^{2 +} proteases (calpains), can contribute to some biochemical changes during storage (Koohmaraie, 1992, 1994, 1996; Alomirah et al., 1998; Schreurs, 2000). However, it has also been generally accepted and shown that detectable organoleptic spoilage of muscle foods is a result of the decomposition and the subsequent metabolite formation caused by the growth and catabolic activity of microorganisms (Stutz et al., 1991; Schmitt and Schmidtlorenz, 1992a,b; Kakouri and Nychas, 1994; Nychas and Tassou, 1997; Braun et al., 1999). These detectable organoleptic changes will vary, for example whether these changes are visible or cause a particular odour, according to the species of colonizing microflora, the general characteristics or type of meat/poultry, processing/production methods and storage conditions (Jackson et al., 1997; García-López et al., 1998).

Several researchers have described meat as the most perishable of all important foods (Jay, 1996; Stanbridge and Davies, 1998), with its nutrient-rich and moist surface being particularly conducive to the colonization and rapid growth of a wide range of spoilage bacteria. The colonization and growth on the meat surface have been widely researched and documented over several decades in some detail, with the initial (and obvious stage) being the attachment of bacterial cells to the meat surface. This has been described as a loose and reversible sorption (Marshall et al., 1971). The second and irreversible stage of attachment involves the production by the bacterium of a sticky polysaccharide extracellular layer, termed the glycocalyx (Costerson et al., 1981), which ultimately leads to a biofilm. Other factors may also play a role in bacterial attachment such as the population of microflora already present in the water film on the meat surface, how motile the species involved are, what growth phase they are in, and purely physical factors such as surface morphology and temperature (Jackson et al., 1997).

In storage conditions conducive to bacterial growth, such as a moist atmosphere and a temperature range between –1 and 25 °C, a wide range of genera are responsible for organoleptic spoilage. Table 1.1 lists the genera most commonly found on meat and poultry and includes both spoilage and pathogenic bacteria. At this particular temperature range and in aerobic storage conditions it is the genus Pseudomonas (including P. fluorescens, P. lundensis, P. putida and P. fragi) which has been observed, in comparison to several other genera responsible for spoilage, to attach more rapidly to meat surfaces (Molin and Ternström, 1982; Jackson et al., 1997; García-López et al., 1998; Stanbridge and Davies, 1998). In aerobic refrigerated storage conditions, the other major spoilage bacter...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributor contact details
• Introduction
• Part I: Detection and analysis of food spoilage
• Part II: Managing food spoilage
• Part III: Spoilage yeasts
• Part IV: Spoilage moulds
• Part V: Spoilage bacteria
• Index