thermal processing 2-value, which is used to calculate the increase or decrease in temperature necessary for a 10-fold difference in the reduction of microorganisms, may also be used to describe pasteurization processes. P-values are usually used, however, because tinlike commercial sterilization processes, both z-value and heat resistance of the organism may increase during pasteurization (4). The heat resistance of microorganisms generally increases in food products having a lower water activity and decreases in food products having a lower pH.
Examples of pasteurization methods include heating mixes and particles suspended in sauces in jacketed vessels, heating liquid or pumpable ingredients via heat exchangers, heating solid particles in atmospheric ovens, frying, and heating packaged products in water baths or retorts for in-pack pasteurization. Any method used must provide a critical minimum heat treatment, which must be defined by heat penetration analyses and thermal death time experiments. Factors affecting the pasteurization process include the initial temperature of the ingredients, amount of solid particulates, equipment heating rate, and rate of circulation/agitation. These parameters, as well as temperature profiles of the finished product during processing, are usually Hazard Analysis Critical Control Points (HACCPs) and must be accurately and reliably controlled and maintained.
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