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

The effect of pH values of 6.5, 6.0, 5.0, and 4.0 on spore germination of Bacillus cereus (B. cereus) was investigatedat water activity (aw) values of 0.98, 0.96, 0.94, and 0.90 in a controlled medium at 30°C for 7 days. The best conditionfor germination of spores of B. cereus was observed at pH 6.5 with aw 0.98. No matter what combination of aw andpH is used, a complete inhibition of spore germination was achieved at either aw 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 pH6.5, 6.0, 5.0, or 4.0. The results indicate that the combined inhibitory effects of pH and water activity on the germinationof B. cereus spores in controlled medium could be applied to food preservation.