Reaction chemistry at high pressure and high temperature

Conventional thermal processing technologies, widely used to increase food safety and stabilize foods, can cause extensive chemical changes in foods. The food industry has been improving conventional and developing new technologies in response to consumers demand for high safety standards and close-to-fresh quality foods with high nutritional value. Pressure-assisted thermal processing (PATP), also called pressure-assisted sterilization (PATS) if the desired level of bacterial spore inactivation is achieved, is an alternative technology based on applying high temperature under high pressure. In the specific case of conduction-heating foods, adiabatic compression heating facilitates reaching temperatures lethal to microorganisms, which, in combination with fast decompression cooling, lowers quality degradation to levels below conventional thermal processing. However, its implementation requires advances in the analysis of reaction kinetics at high pressure and elevated temperature. Unfortunately, very few studies have focused on PATP effects on chemical reaction rates of quality factors at the temperature and pressure levels required for the sterilization of low-acid foods. Even fewer studies have focused on the effect of pressure on thermal degradation reactions known to form toxic compounds. At present, it is not possible to predict whether pressure will increase or decrease the rate for the degradation of quality factors and the formation of toxic compounds unless its activation volume value (V_a) is determined experimentally. Reactions with negligible rate under conventional pressure are of particular interest because they could become important in PATP-treated foods if their V_a value is negative and large. Such reactions will be greatly accelerated by pressure and could constitute a significant cause of safety risk and quality degradation. The evaluation of the safety risk in PATP-treated foods is therefore necessary but this need is still largely ignored by funding agencies in the USA. For example, temperatures in excess of 120 °C are required for a detectable formation of acrylamide in foods treated conventionally, but if this reaction had a large negative V_a value, significant levels could be formed at lower temperatures and high pressure. Although a recent model solution study conducted in Europe demonstrated that acrylamide formation is actually inhibited by pressure, this favorable finding must be confirmed with experiments in actual foods.