Combined effect of nisin and carvacrol at different pH and temperature levels on the viability of different strains of Bacillus cereus

The influence of pH and temperature on the bactericidal action of nisin and carvacrol on vegetative cells of different Bacillus cereus strains was stu died. The five strains tested showed significant differences in sensitivity towards nisin, at pH 7.0 and 30 degreesC. Carvacrol concentrations of 0.3 mmol l(-1) had no effect on viability of B. cereus cells. When the same car vacrol concentration was combined with nisin, however, it resulted in a gre ater loss of viability of cells than when nisin was applied alone. The conc entration of carvacrol played an important role on the bactericidal effect of nisin and, therefore, on the synergistic action of both compounds combin ed. At lower pH values (6.30 and 5.75), nisin was more active against B. ce reus cells than at pH 7.0 at 30 degreesC, with a different sensitivity of t he strains tested. The combined effect of nisin and carvacrol was found to be significantly different at pH 7.0 and 5.75. When the temperature was 8 d egreesC, nisin was significantly less active against B. cereus IFR-NL 94-25 than at 30 degreesC, both at pH 7.0 and 6.30. At 8 degreesC, there was a s ignificant increased effect of nisin at lower pH values. Also at this low t emperature, a synergistic effect between nisin and carvacrol on B. cereus c ells was observed at the pHs tested. This study indicates the potential of nisin and carvacrol at lower pHs to be used for preservation of minimally p rocessed foods. (C) 2001 Elsevier Science B.V. All rights reserved.