Listeria monocytogenes inactivation kinetics under microwave and conventional thermal processing in a kiwifruit puree

Abstract

The inactivation of Listeria monocytogenes in a kiwifruit puree by conventional and microwave heating was studied. Survival curves at three microwave power levels (600–1000 W) and three temperatures (50–60 °C) were obtained. Data were properly fitted by a first-order kinetic model. Processing times under both technologies were corrected to isothermal treatment for the kinetic study. Microwave heating was shown to effectively inactivate L. monocytogenes. In the range of microwave and conventional processing conditions assayed, the 5-log10 reductions of L. monocytogenes recommended by the FDA for pasteurized products were achieved. The level of microwave power applied had a considerable influence on the L. monocytogenes inactivation rate. The higher the power level, the faster the inactivation. The inactivation of L. monocytogenes under microwave heating at 900 W (D60 °C = 17.35 s) and 1000 W (D60 °C = 17.04 s) happened faster than in a conventional thermal process (D60 °C = 37.45 s). Consequently, microwave heating showed greater effectiveness for L. monocytogenes inactivation than conventional heating. Consumers' desires are oriented towards new foods that are convenient, easy to preserve and ready-to-eat products, being consumption of fresh fruit replaced with processed fruit products. Food industry is currently focused on the development of novel and minimally processed products with improved quality. Thus, a variety of new processing technologies are being explored as alternative to traditional thermal processing. In this work, the thermal and microwave inactivation kinetics of Listeria monocytogenes in a ready-to-eat kiwifruit puree were investigated so as to assess the suitability of microwave processing as an alternative to thermal processing. The results of this study point out that more than conventional heating, microwave technology can be an appropriate means of fruit product pasteurization with the possibility of offering the required safety by using a lower process time, when microwave power of a certain level is applied.