Destruction of Indigenous Bacillus Spores in Soymilk by Heat ¹

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 × 10³ 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 × 10⁶ Bacillus spores/ml, 3.4 × 10⁴ 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.