The influence of the temperature of sporulation on the heat resistance of Bacillus subtilis in citrate-phosphate buffer of different pH values was investigated. The effect of the pH of the heating menstruum on the heat resistance of spores was strongly influenced by the temperature
of sporulation. Spores sporulated at 32°C were at pH 4 much less heat resistant (1/6) than at pH 7. This difference in heat resistance at both pH values was constant regardless of the temperature of treatment. On the contrary, in spores sporulated at 52°C the effect of acid pH on heat
resistance was not constant and decreased as heating temperature increased. At 120°C heat resistance was the same at both pH values: z values for pH 7 and 4 were 8.7 and 11.6, respectively. The observed increase of the z value of B. subtilis at pH 4 when sporulated at high temperatures
is an added risk that should be taken into account in hot climates, especially when designing sterilization processes at high temperatures for acid/acidified foods.
Tecnología de los Alimentos, Facultad de Veterinaria, Miguel Servet 177, 50013- Zaragoza, Spain
Publication date: March 1, 1995
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