Validation of Thermal Processing Using Time-Temperature Indicators as Process Probes

Abstract

1.1 Thermal processing Thermal processing is the basis for the majority of the operations of the food industry, with processes such as canning being the basis for large industry sectors. The aim of thermal processing is to reduce the bacterial load in the food to a level that allows it to be safe over the proposed shelf life of the material. In addition, reactions that lead to the creation of acceptable taste and flavour (such as the gelatinisation of starch, the denaturation of proteins, and Maillard reactions) should be promoted, whilst those which lower quality (such as, for example, the loss of vitamins or the creation of carcinogens such as acrylamide) minimised. The practical problem is that the need for process safety is paramount – the damage done to a brand by the need to recall product, or a food poisoning outbreak, is so severe that processes are routinely overdesigned. The result is lowered product quality, which in turn makes the material less attractive to the consumer. The job of the food engineer is to ensure that the quality of the food is maximised while maintaining safety. In part this is an optimisation process and can be highly mathematical [1-3]; however in practice the critical issue is in validating the process. Such validation requires that there is an effective measurement method which can show the level of thermal treatment which the material has received. In some cases, it is possible to measure the temperature-time profile of the food accurately, and thus infer the amount of processing it has received using equations such as: