Survival of heated Bacillus coagulans spores in a medium acidified with lactic or citric acid

The influence of the intensity of heat treatments on the capacity of citric or lactic acid to prevent growth of survivors of Bacillus coagulans spores after 10 days storage at 35°C was studied. In most cases, the number of survivors during storage decreased. The extent of this spore inactivation depended on the intensity of previous heat treatment and the pH of the medium and the acidulant used. The inactivating effect of storage was pronounced even at pH values less acidic than those used by the canning industry. Citric acid was more effective than lactic acid on spores given only low heat treatments, but lactic was more effective against those given more severe heat treatments. The severity of heat treatment required for lactic to be more effective than citric acid increased with pH of the medium. Heat treatment also required increased pH for heated spores to grow. pH 4.6, regardless of acidulant used, was unable to prevent growth of unheated spores but a less acidic pH (pH 5.2) did prevent growth even when spores had been given only mild heat treatments (10 s at 100°C).