INHIBITION OF ALCOHOLIC FERMENTATION BY SORBIC ACID

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Abstract
Sorbic acid inhibition of alcoholic fermentation by intact cells of baker''s yeast is dependent on the pH. However, inhibition of fermentative activity of cell-free extracts prepared by blending in an Omnimixer with fine glass beads was not affected by pH. Therefore, it is believed that the pH effect observed with intact cells results from the greater permeability of the cell to the undissociated form of the acid. Using cell free extracts, 5 x 10-3 [image] sorbic acid was shown to inhibit CO2 production equally from glucose, fructose 1,6-diphosphate and 3-phospho-glyceric acid. However, there was no evidence of any inhibition of aldolase, 3-phosphoglyceraldehyde dehydrogenase, phosphoglyceromutase, phosphopyruvic acid transphosphorylase, carboxylase, or alcohol dehydrogenase. Therefore, the conversion of 2-phosphoglyceric acid to phosphoenolpyruvic acid by enolase appeared to be the only reaction inhibited in the fermentation of glucose by cell free extracts. Experiments with purified yeast enolase demonstrated that this enzyme was sensitive to very low levels of sorbic acid. The degree of inhibition was dependent on both the substrate and inhibitor concentrations but the type of inhibition appeared complex.

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