Effect of pH, acidulant, time, and temperature on the growth and survival of Listeria monocytogenes

The effect of different acids, pH, incubation time, and incubation temperature on the growth and survival of four strains of Listeria monocytogenes in tryptic soy broth was compared. Hydrochloric acid (HCl), acetic acid (AA), lactic acid (LA), malic acid (MA), and citric acid (CA) were used to acidify tryptic soy broth to pH values 4.4, 4.6, 4.8, 5.0, and 5.2 pH. Incubation times were 1, 3, 7, 14, and 28 d at 10, 25, and 35 degrees C. The inhibition of L. monocytogenes in the presence of high acidity appears to be a function of acid and incubation temperature. Based on equal pH values, the antimicrobial activity is AA greater than LA greater than CA greater than or equal to MA greater than HCl at all incubation times and temperatures. When based on equal molar concentration, the activity appeared to be CA greater than or equal to MA greater than LA greater than or equal HCl at 35 and 25 degrees C, and MA greater than CA greater than AA greater than or equal to LA greater than HCl at 10 degrees C. Greatest antimicrobial activity occurred at 35 degrees C. Greatest survival occurred at 10 degrees C and greatest growth occurred at 25 degrees C. Final pH of the medium was as low as 3.8 in HCl at 28 d. All strains grew well at pH values lower than the minimum previously reported (5.5-5.6)