Efficacy of several organic acids against molds

The efficacy of several organic acids against growth of molds typically found in animal feed was determined. A plate assay was used in which paper disks soaked in a spore solution were placed on the surface of agar plates containing increasing concentrations of the respective organic acid. Mold growth radiated from the disks, and the radius was considered indicative of the degree of inhibition as compared to a control. The efficacy of each of the organic acids against the various molds varied substantially. Valeric acid, propionic acid, and butyric acid displayed the highest efficacy against all molds with the effective concentrations ranging from 0.05 to 0.25%. Other acids, including acetic acid, lactic acid, and benzoic acid, required concentrations of 10 lb/ton or more for effective mold inhibition. Susceptibility of molds to inhibition by organic acids was in the order Fusarium spp. > Aspergillus spp. > Penicillium spp., with Fusarium spp. being the most susceptible mold.