Effect of pH and Water Activity on Heat Resistance of Spores of Bacillus coagulans

Abstract

Heat resistance parametric value, D (Decimal reduction time), was investigated to estimate the sterilizing value to inactivate spores of Bacillus coagulans in a food product having a specific combination of pH and water activity (Aw) values. The spores were heated and cultured in a medium containing 0.1% polypeptone, 0.3% yeast extract, 0.2% beef extract, and 0.1% glucose and adjusted to the desired pH and Aw. The minimal growth pH was 4.5 at Aw ca. 1. The minimal growth Aw at pH 7.0 was 0.98 in the medium to which sodium chloride was added as the solute, 0.97 to 0.98 for potassium chloride, 0.94 for sucrose and 0.92 for glycerol.
The apparent D value was determined for sodium chloride at a combination of pH, 4.5 to 7.0, and Aw, 0.98 to 1. Based on the data obtained, a mathematical formula for estimating the D value at an individual co-bination of the two factors was developed.