Inhibitory combinations of nisin, sodium chloride, and pH on Listeria monocytogenes ATCC 15313 in broth by an experimental design approach

The influence of pH (5.0-8.2), NaCl concentrations (0-6% w/v), and incubati on time (0-24 h) on the inhibitory activity of nisin (0-100 I.U./ml) agains t Listeria monocytogenes (10(3) cfu/ml) was studied using the Doehlert expe rimental design and was confirmed by kinetic experiments. predicted values were in agreement with experimental values. Experiments were carried out at 22 degrees C in reconstituted TSB-YE1 broth with or without NaCl. Nisin ha d an immediate pH-dependent bactericidal effect, which increased with decre asing pH values. in modified TSB-YE1 broth without NaCl, the bactericidal e fficacy of nisin (50 I.U./ml) was maximum at pH 6.6. with no L. monocytogen es survivors until 120 h at 22 degrees C. Nisin (50 I.U./ml) action decreas ed in the presence of NaCl, with a minimal inhibitory effect between 2 and 4%. This partially protective effect was cancelled at higher levels of nisi n. (C) 2000 Elsevier Science B.V. All rights reserved.