In order to use the range of food-grade preservation methods available optimally, it is important to understand their characteristics, and any interactions that occur between them. Preservation is intended to prevent or retard deterioration that may otherwise be inevitable in co-product streams or end-products due to the effects of changes in their biochemical, chemical, physical or microbiological state. However, what follows deals with measures to control micro-organisms. The methods of preservation described aim to either kill the micro-organisms, or prevent or retard their multiplication. By so doing, the methods of preservation should aim to prevent microbiological spoilage, but should also prevent the growth (and preferably survival) of, and production of toxins by, food-poisoning micro-organisms.
Typically, substrates that support microbial growth have a naturally occurring microflora, the growth of which may be desirable (for example in cheese or yoghurt). If the growth of these associated micro-organisms is not controlled then microbiological deterioration, causing subtle changes in the characteristics of the product, may occur (e.g. increased acidity in dairy products). Microbiological spoilage is often much more in evidence, however, when contaminating micro-organisms grow in, or on the surface of, products, and produce characteristics that are typical of the particular substrate and micro-organism concerned. This combination is then clearly recognisable as spoilage. Examples are the growth of moulds or surface films of yeasts and bacteria, and the production of gas due to the growth of fermentative yeasts.
The presence and multiplication of potentially pathogenic bacteria are frequently less obvious. For example, food-poisoning bacteria may multiply to infective concentrations without causing any noticeable change in the organoleptic properties of products. In some cases the multiplication of pathogenic micro-organisms is paralleled by the growth of spoilage microorganisms, which results in spoilage and deters consumption of the product, although this is by no means always so. Inadequate food preservation, therefore, may result either in significant public health hazard, due to the growth of potentially pathogenic micro-organisms, or in wastage of products due to the growth of spoilage micro-organisms.
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