Combined effect of pH and water activity on inhibition of spore germination of Bacillus cereus

The effect of pt-I values of 6.5, 6.0, 5.0, and 4.0 on spore germination of Bacillus cereus (B. cereus) was investigated at water activity (a%) values of 0.98, 0.96, 0.94, and 0.90 in a controlled medium at 30°C for 7 days. The best condition for germination of spores of B. cereus was observed at pH 6.5 with aw 0.98. No matter what combination of a and pH is used, a complete inhibition of spore germination was achieved at either a,.. value of 0.90 or pH value of 4.0. Spore germination was also delayed or inhibited at aw 0.98 with pH 4.0, aw 0.96 with pH 5.0, and aw 0.94 with pH 6.5, 6.0, 5.0, or 4.0. The results indicate that the combined inhibitory effects of pH and water activity on the germination of B. cereus spores in controlled medium could be applied to food preservation.