Effect of surfactants and dispersed components on the activity and reactivity of sorbic acid

In common with many other carboxylic acids, sorbic acid shows significant solubility in aqueous and non-aqueous solvents. The presence of a non-aqueous phase (e.g. fat) can markedly affect the concentration of the preservative in the aqueous phase. Solute distribution between the two phases is pH- and concentration-dependent. The presence of dissolved surfactants in the aqueous phase will also affect the activity of sorbic acid. This effect is due to the partitioning of the solute into surfactant micelles. The presence of dispersed components and surfactant micelles also has a marked effect on the reactivity of sorbic acid. Whereas thiols react slowly with sorbic acid, the rate of reaction is increased many-fold by the addition of low molecular weight surfactants. The mechanism of this catalysis will be explained. It has been suggested that sorbic acid inhibits enzymes by reacting with sulphydryl groups of the proteins. Kinetic data from model system studies suggest that the sorbic acid-thiol reaction may be too slow for it to be an obvious means of enzyme inhibition. However, this does not take account of possible catalysis of the reaction in the microenvironment of the protein, perhaps in a manner similar to that identified with low molecular weight surfactants.