Estimation of Listeria monocytogenes survival during thermoultrasonic treatments in non-isothermal conditions: Effect of ultrasound on temperature and survival profiles.

Estimation of Listeria monocytogenes survival during thermoultrasonic treatments in non-isothermal conditions was determined considering an increment from 45 to 70 °C, assessing the adequacy of predictions through experimental data obtained in laboratory media model systems. In order to characterize the sonication effect on the survival pattern, observed behavior was compared to that obtained when only thermal treatment was applied. A noticeable impact on L. monocytogenes survival in non-isothermal conditions was observed when heat is combined with ultrasound, since the sonication effect modifies not only the temperature profile, but also the dynamic survival pattern. It was observed that both treatments were able to achieve a reduction of 5.5 log cycles of the initial population, although the inactivation temperature and the required time to reach such temperature were lower for thermoultrasonic treatments than for thermal treatments. Furthermore, as the temperature dependent parameters required to estimate the dynamic responses in non-isothermal treatments were initially determined from isothermal conditions, the sonication effect on these parameters and its implications for dynamic estimations, which are closely related to the nonlinearity of the systems, were also addressed; for thermal treatments, obtained isothermal curves were properly described by the Weibull model and first order kinetics, while for thermoultrasonication treatments a clear non-linear behavior was observed and only the Weibullian model was able to adequately describe the inactivation pattern.