Thermal Inactivation of Heat-Resistant Bacterial Spores in Milk Concentrate at Ultra-High Temperatures

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Abstract
The heat resistance of spores of Bacillus coagulans WH-9, B. stearothermophilus 1518 and Clostridium sporogenes (PA 3679) at high temperatures was determined in 3:1 milk concentrate and 0.067 [image] phosphate (pH 6.2). Although spore inactivation was predominantly logarithmic, the survivor curves were curvilinear during the initial period of heat transfer from heating medium to contents of thermal inactivation tubes. Spores of B. stearothermophilus required a very high heat activation treatment to obtain maximal spore counts; and the germination of these spores was inhibited by the milk concentrate. F and z values for spores of the cultures in the milk concentrate and phosphate buffer are given. A thermal process of 295 F for 3.5 sec. for the 3:1 milk concentrate (including come-up time), was adequate to inactivate large numbers of B. coagulans and PA 3679 and low numbers of B. stearothermophilus spores.

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