Ohmic heating inactivation of Alicyclobacillus acidoterrestris spores in apple and cranberry juice

This work explored the use of ohmic heating (OH) for inactivating Alicyclobacillus acidoterrestris spores in apple and cranberry juices in comparison to conventional heating (CH). Experiments were conducted at different field strengths (30, 40, 50 V/cm) and end-point temperatures of 90 °C, 100 °C, 110 °C, with CH trials designed to match OH's heating rates. The spore inactivation kinetics were determined at 100 °C, and modeled using log-linear, Weibull, modified Gompertz, and empirical sigmoid models. OH, consistently achieved faster and more complete spore inactivation compared to CH, particularly at 110 °C, where OH reduced viable spores below the detection limit (100 CFU/ml) from an initial spore population in the range of 10⁷–10⁸ CFU/ml, even at the lowest field strength tested. A key finding was that regardless of whether the mode of heating is OH or CH, spore inactivation was influenced not only by temperature but also by the rate at which the target temperature is reached—highlighting the importance of heating rate. In addition, the synergy between electric field strength and temperature resulted in further acceleration of lethality. Our work showed that accelerated inactivation may be obtained without a holding period, especially when high field strengths and temperatures are used simultaneously to achieve a final set point, suggesting that A. acidoterrestris may be controlled using this approach, with potential improvements in juice quality.