Heat Resistance of Bacillus subtilis in Buffer and Foods of Different pH

Heat resistance of a strain of Bacillus subtilis was measured in homogenized canned mushrooms, peas, lentils, meat balls, and tomato; in rehydrated potato purée; and in buffer at selected pH values, to detect any influence of pH and/or-menstruum upon heat resistance. Heat resistance experiments were carried out under continuous monitoring of pH. D_t = 1 min in buffer at pH 4.2, 5.2, 6.1, and 7.1 was obtained at 89.1, 97.3, 104.4, and 107.1°C, respectively. The effect of pH was lower the higher the temperature of treatment. The z values ranged from 6.4 at pH 7.1 to 10.3 at pH 4.2. Heat resistance was mainly dependent on pH of food, but an influence of the food itself was also observed. The pH influenced z value in McIlvaine buffer but not in foods. Prediction of heat resistance values in foods from data obtained in buffer at the same pH is unadvisable as it may lead to errors. These errors will become greater in acid foods the higher the temperature of treatment.