Interacting Effects of pH and NaCl on Heat Resistance of Bacterial Spores

Spores of PA3679 ( C. sporogenes) and Clostridium botulinum 213B were less heat resistant when heated in a menstruum of decreasing pH. The D value of the spore population decreased by 50% when heated in pH 5.0 buffer compared to pH 7.0 buffer. Addition of NaCl to the recovery medium reduced the number of colony forming units in a population of heated spores. Presence of NaCl at 2.0% in the recovery medium decreased the spore D‐value by 20‐40% irrespective of pH of the heating menstruum. Combined effects of pH and NaCl could be illustrated by three‐dimensional histograms.