Propanoic acid

The metabolic fate of propionates varies in different microorganisms. Some have enzyme systems that can convert succinate to propionyl-coenzyme A and through various further steps to propionate, CO2, or propionyl phoshpate. Still others can convert propionic acid to B-alanine or directly to CO2. Whatever the case, the inhibiting effect for microbials is likely related to competition with acetate in the acetokinase system, to the blockage of pyruvate conversion to acetyl-coenzyme A and to interference with B-alanine in pantothenic acid syntheses.

Moreover, other studies suggest the antimicrobial activity of propionic acid revolves around its ability to reduce the pH of its immediate environment to levels of acidity that are harmful to pathogenic microbes as well as its ability to dissociate such that its lipid soluble undissociated form is capable of entering microbial cells. Additionally, there are also studies that suggest that propionic acid's antifungal activity may be the result of propionyl-CoA inhibiting glucose metabolism in certain species of fungus via the accumulation of the CoA-derivative.