EFFECT OF RELATIVE-HUMIDITY OF HOT AIR ON THE HEAT-RESISTANCE OF BACILLUS-CEREUS SPORES

The heat resistance to hot air of spores of Bacillus cereus (ATCC 1457 9) attached to carriers of stainless steel or silicone rubber was inve stigated in a range from 1% to 100% relative humidity (RH). Apart from an initial stage, linear survivor curves were obtained for all relati ve humidities. Neither the attachment itself nor the material of the c arrier had an influence on the resistance. A distinct maximum of heat resistance was found at 40% RH. At 122 degrees C the rate constants at 40% RH were five orders of magnitude smaller than at 100% RH and two orders of magnitude smaller than at 1% RH. At relative humidities of m ore than 40% the rate constants were strongly temperature dependent, w hereas at lower relative humidities they were less temperature depende nt. No significant influence of the relative humidity on the Arrhenius activation energy was found within each humidity range. The mean valu es were 295 kJ mol(-1) for relative humidities of 60% to 100% RH and 1 65 kJ mol(-1) for 1% to 20% RH. The occurrence of a maximum is ascribe d to the existence of two inactivation mechanisms, the first is retard ed and the second is accelerated by a reduction of relative humidity. It is assumed that the first mechanism is a protein denaturation. The second mechanism may be an oxidative process.