Effect of environmental parameters on growth kinetics of Bacillus cereus (ATCC 7004) after mild heat treatment

Abstract

The influence of temperature (10 to 50 °C), initial pH (4.0 to 6.0) and sodium chloride concentration (0.5 to 3.0%) on the growth in nutrient broth and in meat extract of Bacillus cereus after mild heat treatment (90 °C—10 min) was determined. B. cereus spores survived after heating and they were able to germinate and grow in both media when post-treatment conditions were favourable. Heated B. cereus did not grow at 10 and 50 °C or in a medium with pH 4.0. Decreasing pH values and increasing levels of sodium chloride decreased growth rate and increased the lag phase of B. cereus. pH 4.5 was unable to prevent the growth of heated spores in a meat substrate with 0.5% NaCl at 12 °C. The combination of pH ≤ 4.5, NaCl concentration ≥ 1.0% and temperatures ≤ 12 °C was sufficient to inhibit B. cereus growth after heat treatment at 90 °C for 10 min, for at least 50 days in nutrient broth and in meat extract. Re-heating at temperatures ≥ 60 °C could control heated B. cereus ATCC 7004 growth.