Influence of pH on heat resistance of spores of Bacillus coagulans in buffer and homogenized foods

The influence of pH of heating menstruum (McIlvaine buffer) on the heat resistance of Bacillus coagulans spores has been investigated and compared with the heat resistance in homogenized tomato and asparagus at pH 7 and 4 at a wide range of temperatures. Spores were less heat resistant in all menstrua at acid pH. The magnitude of this effect was greatest at the lowest heating temperatures tested, z values in buffer increased from 8.9 degrees C at pH 7 to 10.5 degrees C at pH 4. pH of menstrua was the main influencing factor, but media composition also influenced heat resistance: at pH 7 heat resistance was similar in all menstrua (D-111 degrees C = 1.6 min) but at pH 4 the heat resistance in homogenized foods (D-111 degrees C = 0.26 min in tomato and D-111 degrees C = 0.28 min in asparagus) was lower than in buffer (D-111 degrees C = 0.49 min). The reduced influence of the acidification of media on the heat resistance of B. coagulans at higher temperatures should be taken into account when a rise in the temperature of treatment for canned vegetables is considered to shorten duration of heat processes. (C) 1999 Elsevier Science B.V. All rights reserved.