Inactivation kinetics of Escherichia coli O157:H7 and Listeria monocytogenes in apple juice by microwave and conventional thermal processing

The inactivation kinetics of Escherichia coli O157:H7 (CECT 4972) and Listeria monocytogenes (CECT 4032) inoculated in apple juice were evaluated under conventional isothermal treatments at four temperatures (55, 60, 65 and 70 degrees C) and microwave heating at four power levels (400, 600, 800 and 1000 W). For both thermal treatments, it was possible to achieve a 5-log(10) reduction, as recommended by the FDA. The survival curves were non-log-linear and were well described by the Weibull model. To compare treatments, the survival ratio was calculated over the time temperature history of the microwaved samples based on the Weibull parameters for conventional heating and it was compared with the experimental data. Results show that microwave microbial inactivation was more efficient than predicted in 18 out of 28 tests, which suggests the existence of enhanced inactivation under microwave heating. Industrial relevance: The growing demands for natural and nutritious foods have promoted the development of preservation technologies to ensure consumer safety and to preserve the original nutritional and organoleptic characteristics of the food. Among the emerging technologies, microwave heating has shown great potential for the continuous pasteurization of fluid foods offering rapid volumetric heating, lower surface temperatures and possible enhanced effects. The result of this study shows that microwave pasteurization of apple juice is a promising technology to enhance microbial safety.