Inactivation kinetics of Bacillus coagulans spores under ohmic and conventional heating

Bacillus coagulans spores are commonly involved in the spoilage of food of pH between 4 and 4.5. Recent studies on ohmic heating have indicated the presence of an additional nonthermal effect of electricity on the bacterial spores of Geobacillus stearothermophilus and Bacillus subtilis. We investigated the kinetics of inactivation of B. coagulans spores (ATCC 8038) in fresh tomato juice under ohmic heating at frequencies of 10 kHz and 60 Hz, and compared it with conventional heating using a specially designed experimental setup that assured identical temperature histories for all treatments. Ohmic heating at 60 Hz showed significantly lower D-values at 95, 100 and 105 °C compared to conventional heating. While 10 kHz also showed a similar trend of higher inactivation compared to conventional heating, the difference was significant only at 105 °C. Both ohmic treatments also showed higher inactivation than conventional heating during the come-up time. In conclusion, ohmic heating resulted in accelerated inactivation of B. coagulans spores compared to conventional treatment.