Detecting Pathogens in Food

Thomas A. McMeekin

• Publisher: Woodhead Publishing
• Year: 2003
• Print ISBN: 9781855736702
• eBook ISBN: 9781855737044
• Topic: Tecnologia e ingegneria
• Subtopic: Scienze dell'alimentazione

Identifying pathogens in food quickly and accurately is one of the most important requirements in food processing. The ideal detection method needs to combine such qualities as sensitivity, specificity, speed and suitability for on-line applications. Detecting pathogens in food brings together a distinguished international team of contributors to review the latest techniques in microbiological analysis and how they can best be used to ensure food safety.Part one looks at general issues, beginning with a review of the role of microbiological analysis in food safety management. There are also chapters on the critical issues of what to sample and how samples should be prepared to make analysis effective, as well as how to validate individual detection techniques and assure the quality of analytical laboratories. Part two discusses the range of detection techniques now available, beginning with traditional culture methods. There are chapters on electrical methods, ATP bioluminescence, microscopy techniques and the wide range of immunological methods such as ELISAs. Two chapters look at the exciting developments in genetic techniques, the use of biosensors and applied systematics.Detecting pathogens in food is a standard reference for all those concerned in ensuring the safety of food. - Reviews the latest techniques in microbiological analysis and how they can best be used to ensure food safety - Examines the role of microbiological analysis in food safety management and discusses the range of detection techniques available - Includes chapters on electrical methods, ATP bioluminescence, microscopy techniques and immunological methods such as ELISAs

Part I

General issues

1

Microbiological analysis and food safety management: GMP and HACCP systems

C.de.W. Blackburn Unilever R&D Colworth, UK

1.1 Introduction

There are two different approaches to deliver food safety, Quality Control (QC) and Quality Assurance (QA). Both systems share tools, but the emphasis is very different. Both approaches are legitimate, but they need totally different organisations, structures, skills, resource and ways of working (Kilsby, 2001). QC is a reactive approach influenced by the pressures in the external world. In a QC organisation the emphasis is on measurement, which needs to be robust and statistically relevant, and the focus is on legal and commercial issues. In contrast, QA is a preventative approach driven by the company’s internal standards. The emphasis is on operational procedures, which must be robust and regularly reviewed, and the focus is on the consumer.

There are several problems associated with relying on testing for product safety assurance (van Schothorst and Jongeneel, 1994). In order to apply any statistical interpretation to the results, the contaminant should be distributed homogeneously through the batch. As microbiological hazards are usually heterogeneously distributed, this means that there is often a major discrepancy between the microbiological status of the batch and the microbial test results (ICMSF, 1986). Even if the microbial distribution is homogeneous, it may still be prohibitive to test a sufficient number of sample units for all the relevant hazards to obtain meaningful information. Perhaps most significantly, microbiological testing detects only the effects and neither identifies nor controls the causes. As a consequence there has been an inexorable move from QC to QA in the management of microbiological hazards in food, with the focus on preventative control measures rather than finished product testing. Although microbiological analysis has subsequently borne the brunt of much denigrating, it still has a vital role to play as part of a QA framework, albeit with a shift in application and emphasis.

1.2 Food safety management systems

Food safety management relies on the interplay of a number of fundamental elements, including:

• Knowledge

• tools (e.g. risk assessment)

• mechanisms (e.g. HACCP) (van Schothorst, 1998; Ross and McMeekin, 2002).

At the centre lies the provision of safe food defined by a food safety objective (FSO), which is a statement of the frequency or maximum concentration of a microbiological hazard in a food considered acceptable for consumer protection. The mechanism by which the FSO is achieved is by application of a number of systems, which have been adopted by the food industry and are used in an integrated fashion. These include good manufacturing practice (GMP), good hygiene practice (GHP) and the hazard analysis critical control point (HACCP) system.

HACCP is a food safety management system that uses the approach of identifying and evaluating hazards and controlling their fate at critical control points (CCPs) in the supply chain. The widespread introduction of HACCP has promoted a shift in emphasis from end-product inspection and testing to the preventative control of hazards during production, especially at the CCPs. It is generally agreed that the most successful implementation of HACCP is done within an environment of well-managed prerequisite programmes (PRPs) (Mortimore and Mayes, 2002). Although definitions vary, the concept of PRPs does not differ significantly from what may be termed GMP. GMP is concerned with the general (i.e. non-product specific) policies, practices, procedures, processes, and other precautions that are required to consistently yield safe, suitable foods of uniform quality. GHP is the part of GMP that is concerned with the precautions needed to ensure appropriate hygiene and as such tends to focus on the prerequisites required for HACCP.

Generally, GMP/GHP requirements include the following:

• the hygienic design and construction of food manufacturing premises

• the hygienic design, construction, proper use and maintenance of machinery

• cleaning and disinfection procedures for plant and equipment

• general hygienic and safety practices in food processing, including:

– microbial quality of raw materials and supplier quality assurance

– hygienic operation of each process step

– hygiene of personnel and their training in hygiene and the safety of food

– pest control

– water and air control

– product rework and recall procedures

– waste management

– labelling and traceability systems

– transportation (Brown, 2002; Mortimore and Mayes, 2002).

For steps in the manufacturing process that are not recognised as CCPs, the use of GMP is essential to provide assurance that suitable controls and standards are present. In turn, the identification and analysis of hazards within the HACCP programme will provide information to interpret GMP requirements and indicate staff training needs for specific products or processes (Brown, 2002).

Although GMP cannot substitute for a CCP, collectively it can minimise the potential for hazards to occur, thus eliminating the need for a CCP. The implementation of effective GMP will control ‘general’ or ‘establishment’ hazards that would otherwise have to be controlled by a CCP. Failure to have GMP in place will inevitably lead to a large number of CCPs in the HACCP plan covering both ‘general/establishment’ hazards and product specific ones.

Food safety management is required from ‘farm to fork’ and systems analogous to GMP have been developed throughout the food supply chain. These include systems targeted at food production: good agricultural practice; good working practices of animal husbandry (Johnston, 2002); and good aquacultural practice; as well as those targeted at food handlers and consumers: good catering practice; and good domestic kitchen practice (Griffith, 2002).

1.3 Types of testing used in GMP and HACCP systems

The types of tests that have a role in GMP and HACCP systems depend on the specific application and range from standard detection and enumeration methods through to the most sophisticated finger printing techniques. Although full details of these methods are covered elsewhere in this book, it is worth taking time to briefly consider the importance of tests for indicator organisms and the application of challenge tests and predictive microbiology models.

1.3.1 Pathogen vs. indicator testing

The numbers of pathogenic microorganisms in most raw materials and food products are usually low and so pathogen tests may provide little information of use for the implementation and maintenance of GMP and HACCP systems. Instead, the enumeration of so-called ‘indicator organisms’ has an important role. Indicator organisms are groups of microorganisms that are indicative for the possible presence of pathogens. Although there is not necessarily a relationship between indicator and pathogen numbers, it can be generally assumed that the possible numbers of a pathogen are less than the numbers of the organisms indicative for it. It can also be assumed that reduction in the numbers of the indicator organisms will produce a similar reduction in the numbers of any corresponding pathogen (Brown et al., 2000). For the same reasons indicator organisms can also provide a measure of post-pasteurisation contamination that might lead to pathogen contamination. As different indicator organisms imply the possible presence of different pathogens, there are several groups of tests that may be appropriate, e.g. total aerobic counts, coliforms, Entero-bacteriaceae, E. coli, faecal streptococci and aeromonads (Brown et al., 2000).

1.3.2 Microbiological challenge testing and predictive microbiology

When assessing the safety of a product and/or process the use of microbiological challenge testing may be required. This type of test can be helpful in determining the ability of a food to support the growth of pathogens and in the validation of processes that are intended to deliver a defined degree of lethality against a target organism (IFT, 2001). In essence microbiological challenge testing involves the inoculation of a food with specific microbial hazards and monitoring their growth, survival or death during storage and/or after specific process steps. However, there are a number of important factors that must b...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributor contact details
• Introduction
• Part I: General issues
• Part II: Particular techniques
• Index