Response surface methodology, an approach to predict the effects of a lactoperoxidase system, Nisin, alone or in combination, on Listeria monocytogenes in skim milk.
Experimental designs using Response Surface Methodology (RSM) were used to determine effects and interactions of Nisin (0-200 i.u. ml-1), pH values (5.4-6.6), incubation time (0-36 h or 0-144 h) and the lactoperoxidase-thiocyanate-hydrogen peroxide system (LPS) on Listeria monocytogenes CIP 82110 in skim milk, at 25 degrees C. The LPS varied from level 0-2; LPS at level 1 consisted of lactoperoxidase (35 mg l-1), thiocyanate (25 mg l-1) and H2O2, which was supplied exogenously by glucose-oxidase (1 mg l-1) and glucose (0.2 g l-1); LPS activity was dependent on LPS level and incubation time. In the presence of LPS at level 1, a bacteriostatic phase was followed by growth, whereas at a higher level, a bactericidic phase was observed. Nisin response was time- and pH-dependent. Nisin was bactericidic at acidic pH values and for a short incubation time (12 h) only; then, a re-growth phase was observed. Nisin and LPS in combination gave an original response which lacked the transitory bactericidal effect of Nisin and had a continuously bactericidal affect, leading to 10 cfu ml-1 of L. monocytogenes at 144 h; the response was greatly affected by incubation time. Predicted values were in good agreement with experimental values. Response Surface Methodology is a useful experimental approach for rapid testing of the effects of inhibitors.
Boussouel
N
N
Laboratoire de Fermentations et Bioconversions Industrielles, ENSAIA-INPL. Vandoeuvre-les-Nancy, France.
Mathieu
F
F
Benoit
V
V
Linder
M
M
Revol-Junelles
A M
AM
Millière
J B
JB
D000818:Animals; D004357:Drug Synergism; D005163:Factor Analysis, Statistical; D005520:Food Preservatives / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007784:Lactoperoxidase / Q000494:pharmacology*; D008089:Listeria monocytogenes / Q000187:drug effects / Q000254:growth & development*; D008892:Milk / Q000382:microbiology*; D009561:Nisin / Q000494:pharmacology*; D013861:Thiocyanates / Q000494:pharmacology*; D013997:Time Factors
D005520:Food Preservatives; D013861:Thiocyanates; D009561:Nisin; D006861:Hydrogen Peroxide; D007784:Lactoperoxidase; C031760:thiocyanate