Fermentation and pathogen control: a risk assessment approach

76M. Adams, R. Mitchell / International Journal of Food Microbiology 79 (2002) 75–833. Hazard identificationFig. 1. Microbiological risk assessment.how this is done has evolved over the last few yearsand has been well described in a number of recentmonographs (Mitchell, 2000; Voysey, 2000; Benford,2001).Essentially, the process consists of the stages outlinedin Fig. 1. The first requirement is to formulate theproblem in a statement of purpose—what is yourobjective in doing the risk assessment. Once this isdone, it is necessary to decide which hazardous organismswill be of concern in the product (Hazard Identification);what will be the intake of hazard as a resultof food consumption (Exposure Assessment); whatwill the effect be on people (Hazard Characterisation);and, finally, what is the overall risk to a givenpopulation (Risk Characterisation).2. Statement of purposeFermented foods can be defined as foods in whichmicrobial activity plays an essential role in conferringthe required stability, safety and sensory propertiesto the product. This definition will exclude thoseproducts which are often described as fermented butare largely the product of nonmicrobial, enzymicprocesses such as black tea and the fish sauces ofSoutheast Asia, but will include those productswhere the principal microbial activity is nonfermentative,such as tempeh and vinegar. When the virtuesof fermentation as a means of preservation arediscussed, however, it is almost invariably in connectionwith those foods where lactic acid bacteria(LAB) play a central role in the production process,and it is these which will be the focus of whatfollows.Identifying which pathogenic agents may be transmittedby fermented foods is clearly an important stepin the overall risk assessment process. Generally, thiswill require expert knowledge and the appraisal ofdata from a variety of sources. The major concern isthat a significant pathogen is not disregarded and toavoid this pitfall, attempts have been made to developstructured and systematic approaches to hazard identification(Notermans et al., 1994; van Gerwen et al.,1997).While we recognise that many pathogens can gainaccess to a product as a result of contamination duringprocessing and storage, raw materials are often theprincipal source of hazards. The range of fermentedfoods is, however, huge (see for example, Wood,1998).They are made using raw materials from all the mainfood commodity groups—meat, fish, milk, vegetables,fruits, grains and pulses, and there is considerablevariation in the unit operations involved in individualprocesses and how the products are stored and consumed(Nout, 2001). As a consequence, the number ofmicrobiological hazards potentially associated withfermented foods can be correspondingly large. It ispossible to edit the extensive lists obtained by examiningepidemiological data from outbreaks where fermentedfoods have been implicated. This informationhas a decided bias since many fermented foods areproduced and consumed in countries that lack highlydeveloped systems for the reporting of foodborne illness.The information we have is therefore largelyrelated to products popular in the developed world,such as fermented milks and meats. Even here, whenwe are considering a more limited range of products, asubstantial list of pathogens can emerge. By way ofexample, a list of pathogens associated with illnesscaused by cheese is substantial and includes mostcommon and some less common foodborne bacterialpathogens (Table 1). Clearly, hazard identification forfermented foods as a whole is not a particularlyilluminating exercise as virtually all the known foodbornepathogens will be included. There is, however, ahierarchy and some pathogens are more common andtherefore pose a greater risk. If we look specifically atfermented sausages then on a worldwide basis, Salmonella,VTEC and Staphylococcus aureus seem to be themain concerns, although there may be some geograph-