THERMAL-RESISTANCE OF BACILLUS-CEREUS SPORES AS AFFECTED BY ADDITIVESIN THE RECOVERY MEDIUM

The effects of the addition of starch, glucose, sodium chloride, sodiu m citrate, monopotassium phosphate and disodium phosphate to the recov ery medium on apparent heat resistance of Bacillus cereus spores (ATCC 4342, 7004 and 9818) were investigated. Sodium citrate, monopotassium and disodium phosphate at concentrations of 0.1% were effective inhib itory agents for heat injured B. cereus spores especially for strain 9 818, although only monopotassium and disodium phosphate caused a signi ficant reduction (p<0.05) in D-values obtained for strain 9818. Sodium chloride also had a marked effect on the recovery of heat injured spo res. Concentration as low as 0.5% caused a significant reduction in th e recovery rates for strains 9818 and 7004. In all cases, increasing t he salt levels from 0.5 to 4% resulted in a progressive decrease in sp ore recovery. D-values gradually decreased as the salt content increas ed, although the concentrations which produced statistically significa nt differences (p<0.05) varied among strains. The addition of starch a t 0.1% resulted in a significant increase in the counts for strains 98 18 and 7004. In contrast, glucose (0.1%), did not significantly modify the counts obtained. Neither of these compounds affected decimal redu ction times. No statistical significance (p>0.05) differences were det ected among z-values for the spores of the three strains recovered in the presence of different additives assayed. z-Values ranged from 6.67 to 8.32, with a mean value of 7.56 +/- 0.46C.