Thermal inactivation of Bacillus cereus spores affected by the solutes used to control water activity of the heating medium

The heat resistance of B. cereus spores (ATCC 7004, 4342 and 9818) over a wide temperature range (92–125°C) in aqueous solutions of NaCl, LiCl, sucrose and glycerol at different water activities (1.00–0.71) was investigated. Sodium chloride in the heating medium tended to protect the spores of B. cereus against heat. The z-values increased significantly (P<0.05) at and above a concentration of 4.0 M. The effects of LiCl were lower than those caused by the NaCl at the same aw values. An increase in z-values was observed, but the differences were only statistically significant (P<0.05) at the highest concentration tested (5.0 M). A concentration of sucrose 0.87 M caused in all cases a reduction in D-values, which was most pronounced for strains 4342 and 9818. With increasing concentration of sucrose (>0.87 M), the D-values showed an increase, although only those obtained for strain 4342 in sucrose solutions 2.22 M were higher than those found in pure water. The z-values were significantly higher (P<0.05) when sucrose was added at concentrations above 1.42 M, except for strain 4342. When aw was lowered from 0.96 to 0.71 with glycerol, D-values obtained gradually increased, about 30, 50 and 60 fold for 4342, 7004 and 9818 strains, respectively. No significant effect on z-values were detected.