Stability of sorbic acid in intermediate moisture systems

Intermediate foods are a heterogeneous group of foods which are stabilized by lowering their water activity to a level insufficient to support bacterial growth, typically about 0.85. However, moulds and yeasts are able to grow at these water activities and it is usual to add an antimycotic such as sorbate to ensure microbial stability. Sorbate, though, is liable to oxidation and in model systems adjusted to a water activity of 0.85 some of the oxidation products were found to be potential reactants in non-enzymic browning reactions with lysine, glutamate and haemoglobin solutions when stored at 38 degrees C or 65 degrees C. Oxidation led to an increase in pH and the formation of thiobarbituric acid-reactive substances. In some intermediate moisture meat products prepared by cook-soak equilibration in a variety of humectant solutions, 0.3% sorbate induced the formation of covalent linkages between proteins on storage at 38 degrees C. The concentration of sorbate in the meats decreased by a factor of 2 during 4 months at this temperature. The effects of such reactions on the quality of the food are discussed.