Inhibition or Inactivation of Listeria monocytogenes by Sodium Benzoate together with some Organic Acids

Abstract

Tests were done to determine the fate of Listeria monocy togenes at 13 or 35°C in Tryptose Broth (TB) with and without the pH adjusted to 5.6 or 5.0 using acetic, tartaric, lactic, or citric acidand containing 0.00,0.05,0.15, or 0.3%sodiumbenzoate. The bacterium grew in all controls (free of benzoate) under all conditions except only slight growth was detectedat 13°C when the pH was adjusted to 5.0 using acetic or tartaric acid. When TB was acidified with acetic or tartaric acid and incubated at 35°C, the bacterium was inactivated or inhibited under all con ditions except growth occurred at pH 5.6 with 0.05 or 0.15% sodium benzoate and at pH 5.0 with 0.05% benzoate. Incubation at 13°C with the same acids in TB was accompanied by inacti vation or inhibition of the bacterium at all testconditions except in the presence of 0.05% sodium benzoate and pH 5.6 obtained by added acetic acid, and in the presence of 0.05 or 0.15% benzoate when tartaric acid was used to adjust the pH to 5.6. Acidifying TB with lactic or citric acid and incubating at 35°C resulted in growth at pH 5.0 and 5.6 regardless of concentration of benzoate except 0.3% which caused inhibition or inactivation at pH 5.6 or 5.0, respectively. Incubation at 13°C with the same acids in TB resulted in inactivation or inhibition of L. monocy togenes, except growth occurred at pH 5.6 when the medium contained 0.05 or 0.15% benzoate. Slight growth was observed in the presence of 0.05% benzoate at pH 5.0 when the medium was acidified by lactic or acetic acid.