Apparent thermal resistance of Bacillus stearothermophilus spores recovered under anaerobic conditions

The effect of recovering Bacillus stearothermophilus spores under anaerobic conditions on their apparent thermal resistance was studied. Spores were suspended in bidistilled water as a reference medium, heated at 115, 117, 119, 121, 123 and 125°C and recovered under aerobic and anaerobic conditions. D values (decimal reduction time) obtained following recovery under anaerobic conditions were lower than those obtained under aerobic conditions. Reductions of between 31 and 48% were found for all the temperatures studied. When spores were suspended in mushroom extract and recovered under anaerobic conditions the apparent heat resistance was much lower than that obtained under aerobic conditions (D121°C was 4.3 min and 1.7 min, under aerobic and anaerobic conditions, respectively). Heating the spores in mushroom extract and recovering the spores under anaerobic conditions produced an additive effect, decreasing the apparent heat resistance of the B. stearothermophilus spores.