SPORULATION TEMPERATURE AND HEAT-RESISTANCE OF BACILLUS-SUBTILIS AT DIFFERENT PH VALUES

The influence of the temperature of sporulation on the heat resistance of Bacillus subtilis in citrate-phosphate buffer of different pH valu es was investigated. The effect of the pH of the heating menstruum on the heat resistance of spores was strongly influenced by the temperatu re of sporulation. Spores sporulated at 32-degrees-C were at pH 4 much less heat resistant (1/6) than at pH 7. This difference in heat resis tance at both pH values was constant regardless of the temperature of treatment. On the contrary, in spores sporulated at 52-degrees-C the e ffect of acid pH on heat resistance was not constant and decreased as heating temperature increased. At 120-degrees-C heat resistance was th e same at both pH values: z values for pH 7 and 4 were 8.7 and 11.6, r espectively. The observed increase of the z value of B. subtilis at pH 4 when sporulated at high temperatures is an added risk that should b e taken into account in hot climates, especially when designing steril ization processes at high temperatures for acid/acidified foods.