The combined effect of pasteurization intensity, water activity, pH and incubation temperature on the survival and outgrowth of spores of Bacillus cereus and Bacillus pumilus in artificial media and food products.
The objective of the study was to evaluate the combined effects of pasteurization intensity (no heat treatment and 10 min at 70, 80 and 90 degC) water activity (aw) (0.960 0.990) pH (5.5 7.0) and storage temperature (7 and 10 degC) on the survival and outgrowth of psychrotolerant spores of Bacillus cereus FF119b and Bacillus pumilus FF128a. The experiments were performed in both artificial media and a validation was performed on real food products (cream, bechamel sauce and mixed vegetable soup) It was determined that in general, heat treatments of 10 min at 70 degC or 80 degC activated the spores of both B. cereus FF119b and B. pumilus FF128a, resulting in faster outgrowth compared to native (non heat treated) spores. A pasteurization treatment of 10 min at 90 degC generally resulted in the longest lag periods before outgrowth of both isolates. Some of the spores were inactivated by this heat treatment, with more inactivation being observed the lower the pH value of the heating medium. Despite this, it was also observed that under some conditions the remaining (surviving) spores were actually activated as their outgrowth took place after a shorter period of time compared to native non heated spores. While the response of B. cereus FF119b to the pasteurization intensity in cream and bechamel sauce was similar to the trends observed in the artificial media at 10 degC, in difference, outgrowth was only observed at 7 degC in both products when the spores had been heated for 10 min at 80 degC. Moreover, no inactivation was observed in cream or bechamel sauce when the spores were heated for 10 min at 90 degC in these two products. This was attributed to the protective effect of fat in the cream and the ingredients in the bechamel sauce. The study provides some insight into the potential microbial (stability and safety) consequences of the current trend towards milder heat treatments which is being pursued in the food industry.
International journal of food microbiology