Inhibition and Inactivation of Listeria monocytogenes by Sorbic Acid

Abstract

Inhibition and inactivation of Listeria monocytogenes by sorbic acid were studied using tryptose broth supplemented with 0, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3% potassium sorbate; adjusted to pH 5.6 or 5.0; and incubated at 4, 13, 21 or 35°C. The bacterium grew in sorbate-free controls under all conditions except at 4°C and pH 5.0. At pH 5.6 and 4°C, the bacterium was inactivated by 0.25 or 0.3% of potassium sorbate after 66 and 60 d. Other concentrations permitted slight growth followed by decreases in populations. At 4°C and pH 5.0, concentrations of 0.15 to 0.3% potassium sorbate completely inactivated the pathogen in 60 to 36 d, whereas the other concentrations caused a gradual decrease in populations during the incubation period. At 13°C and pH 5.6, L. monocytogenes grew at all test concentrations of potassium sorbate, but the maximum populations were directly related to the concentration of potassium sorbate added to the medium - the higher the concentration, the lower the ultimate maximum population. At 13°C and pH 5.0, concentrations of 0.2, 0.25 or 0.3% potassium sorbate completely inhibited growth and caused complete inactivation of the pathogen, whereas presence of 0.15% or less potassium sorbate allowed growth of the pathogen. At 21 and 35°C and pH 5.6, appreciable growth of L. monocytogenes occurred at all test concentrations of sorbate. Reducing the pH to 5.0 allowed limited growth of the pathogen at 21 and 35°C when the medium contained 0.05, 0.1 or 0.15% potassium sorbate. Higher concentrations caused either complete inhibition or inhibition plus partial or complete inactivation of L. monocytogenes.