Microbiology Food Testing - Setting Microbiological Specifications
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By now we should understand the basics of why we need to test, how testing is performed and how to 'manipulate' the figures on the test certificate. But what about the actual results for particular bacteria? What are we to make of them and what should be expected to be acceptable levels? What if there are no specific regulations or guidelines? In these cases a bit of knowledge regarding ingredient s, processing and expected shelf-life need to be considered. If your finished product contains raw meat, the APC count will most likely be high e.g. 1 x 106 cfu/g; likewise any salad or raw vegetables will give similarly high results. This is because such products contain "dirty" ingredients with high microbial loadings and although the majority of these organisms will be perfectly harmless, many will become responsible for spoilage development if the product is stored inappropriately. Specification will therefore need to take account of the likely starting levels of bacteria, but always work on the basis that the better t he quality t he raw materials, the better the end product result will be in shelf life durability.
Most concern regarding amount and frequency of testing should be reserved for ready-to-eat high-risk products, which are suitable for t he multiplication of bacteria during chilled storage and require no further cooking prior to consumption. Enteric pathogens like Salmonella and E. coli 0157 should be absent. For indicator organisms, e.g. Coliforms and Enterobacteriaceae, consideration needs to be given in relation to the product being tested. If the product has undergone any reasonable heat process, be it pasteurization, cooking etc., these groups of bacteria should be absent as hey are heat sensitive. Their continued presence in such a product indicates failure during heating, or more likely, recontamination from the cooling step onwards. Where potential pathogens are concerned, e.g. Staphylococcus aureus, Bacillus cereus or Clostridium perfringens, they may only cause illness if present in high numbers e.g. greater than 104 per gram, thus when setting limits for these type of bacteria, low numbers e.g. in the low hundreds are acceptable to balance the quest between producing safe food and succeeding in regularly passing realistic microbiological specifications.