Behavior of Listeria monocytogenes at 7, 13, 21, and 35°C in Tryptose Broth Acidified with Acetic, Citric, or Lactic Acid.

Inhibition of Listeria monocytogenes CA and V7 by of acetic, citric, and lactic acids at 7, 13, 21, and 35°C was investigated. Statistical analysis showed interactive effects between temperature, types, and concentration of acids and strains of the pathogen. Presence of up to 0.1% of acetic, citric and lactic acids in the medium (tryptose broth) inhibited growth; the degree of inhibition increased as the temperature of incubation decreased (no growth occurred in the presence of 0.1% acetic acid at 7°C). L. monocytogenes was inactivated at all temperatures when acid concentrations in the medium were 0.3% or greater. Acetic acid was most detrimental to L. monocytogenes followed in order by lactic and citric acids. The antilisterial activity of these acids coincided with their degree of undissociation. Citric and lactic acids, with larger dissociation constants, were less detrimental to the pathogen than was acetic acid.