Food Safety I

The agar diffusion assay was used to examine the effect of pH on the ability of alkaline salts of 3 fatty acids (FA) to inhibit growth of bacteria associated with poultry processing. FA solutions were prepared by dissolving 0.5 M concentrations of caprylic, capric, or lauric acid in separate aliquots of 1.0 M potassium hydroxide (KOH). Citric acid was added to the FA-KOH mixtures to reduce the pH of separate portions of the solutions to 9.5, 10.5, 11.5, 12.5, or 13.5. Solutions were sterilized by passage through 0.2 μm filters. Agar media was then prepared, sterilized, tempered to 50°C, and inoculated with 106 colony-forming-units/ml of Campylobacter jejuni, Escherichia coli, or Salmonella Typhimurium. Inoculated agar was poured into Petri dishes and allowed to solidify. Wells were made in solidified agar, and 0.1 mL of FA-KOH solutions was added to separate wells. Inoculated agar plates were incubated, and zones of inhibition of bacterial growth around the wells filled with FA-KOH mixtures were measured. Results indicated that reducing the pH of caprylic acid-KOH to 13.5 and the pH of capric acid-KOH mixtures to 12.5 produced significant (P < 0.05) decreases in the size of zones of inhibition of C. jejuni, but reducing the pH of these solutions to 9.5 produced no differences in the size of zones of inhibition of E. coli. However, while lowering the pH of caprylic acid-KOH solutions to 13.5 produced a significant reduction in the size of zones of inhibition of Salmonella Typhimurium, decreasing the pH of capric acid-KOH mixtures did not result in changes in the size of zones of Salmonella Typhimurium. Lowering the pH of lauric acidKOH solutions to 12.5 produced significant decreases in the size of the zones of inhibition of all 3 isolates. Findings demonstrated that the pH of solutions of alkaline salts of FA may play a role in the antibacterial activity of these surfactants toward bacteria associated with poultry processing. Therefore, the pH of FA-KOH mixtures should be considered when formulating these solutions for use as poultry processing sanitizers.