Reactions in food systems: negative temperature coefficients and other abnormal temperature effects

Abstract
Summary. The rate of a chemical reaction in a simple system normally increases when the temperature is raised, but there are a number of apparent exceptions to this rule when more complex systems are used. When the rate of production or disappearance of a single component in a multi‐component system is considered there are a number of examples of interest to the food scientist and technologist where the apparent rate of reaction decreases when the temperature is raised. Examples of this phenomenon, involving fats, proteins, carbohydrates and vitamins are introduced, and the circumstances under which rates of reactions can show a negative temperature coefficient are discussed. It is concluded that this type of effect can usually be related to the fact that the change in rate of reaction is being measured in a system where conditions other than temperature (e.g. rates of concurrent reactions, concentrations of reactants, phase conditions) are being allowed to vary and the rate is being compared in different systems as well as at different temperatures. It is pointed out that accelerated storage tests at elevated temperatures may give misleading results under these circumstances and that cool or cold storage of foodstuffs may not necessarily be beneficial in all respects.