Destruction of Indigenous Bacillus Spores in Soymilk by Heat

Abstract

Boiling of soymilk in preparation for soy yogurt production does not destroy the indigenous Bacillus spores which may affect the fermentation process. Soymilk (2.2 × 10(3) CFU/ml) boiled for 1 min in a Microwave had 33 CFU/ml, steamed for 20 min at 110°C had 25 CFU/ml, and autoclaved at 121°C for 15 min had no detectable organisms (<1 × 10). Soy yogurt made from these heat-treated soymilks had 4.2 × 10(6) Bacillus spores/ml, 3.4 × 10(4) Bacillus spores ml, and no detectable spores, respectively. We recommend autoclaving (121°C, 15 min) soymilk before performing research work on microbiology and biochemistry of soy yogurt fermentation.