Estimating the efficacy of mild heating processes taking into account microbial non-linearities: A case study on the thermisation of a food simulant (original) (raw)

Which heat process value F should a particular food receive to make it safe and shelf stable? * Section 1 lists reported sterilization values F0 = F zero (reference temperature 121.1 oC; z = 10 oC) for commercial food preservation processes of all types of food products, for several package sizes and types. * Section2 contains reported pasteurization values F, or P, of a great variety of foods. The required storage conditions of the pasteurized foods, either at ambient temperature, or refrigerated (4 - 7 °C), are indicated. * Section 3 shows a decision scheme: should a particular food be pasteurized or sterilized? This depends on the intended storage temperature (refrigerated or ambient) after heating, the required shelf life (7 days to 4 years), the food pH (high acid, acid, or low acid), the food water activity aW, and on the presence of preservatives such as nitrite (E250) mixed with salt NaCl, or nisin. * In Section 4, two worked examples are presented on how to use an F value when calculating the actual sterilization time Pt: - C.R. Stumbo’s (1973) calculation method has been manually applied, verified by computer program STUMBO.exe, to find the sterilization time and the thiamine retention of bottled liquid milk in a rotating steam retort; - O.T. Pham’s (1987; 1990) formula method, incorporated in Excel program “Heat Process calculations according to Pham.xls”, has been used to find the sterilization time and the nutrient retention of canned carrot purée in a still steam retort. * The worked example in Section 5 illustrates the use of the pasteurization value F of apple juice, in calculating the required (average) residence time in the holding tube of a heat exchanger. The Excel program Build-Heat-Exchanger.xls next calculates the juice’s spoilage rate by a mold, a yeast and an enzyme, and the nutrient retention of vitamins C and folic acid in the pasteurized juice. * Section 6 explains how F values can be calculated when a microbial analysis of the food is available. The actual pasteurization or sterilization time calculations should be based on all micro-organisms of concern present, and rather NOT on the highest F value only! An example calculation shows that the required F value for a food, to be sold in a moderate climate country, usually differs considerably from the F, required for the same food, to be sold in tropical areas.