Abstract

Enzyme inactivation can be the target of a pasteurization process of fruit juices. Fresh cloudy apple juice was subjected to continuous flow microwave assisted pasteurization in a pilot scale unit at three processing temperatures (70 degrees C, 80 degrees C and 90 degrees C), two flow rate levels and two heating systems (conventional and focused microwave). A heat transfer model was developed and combined with mean residence time information to provide the average time-temperature history of the product. Inactivation kinetics (first order with two fractions) was used to calculate the integrated lethality. The thermal model was validated with measurements along the product path and the final residual activity was compared with the model prediction. Good results were obtained for polyphenol oxidase (PPO) and peroxidase (POD) but not for pectin methylesterase (PME), which showed to be the most resistant enzyme. Focused microwave heating resulted in a high heating rate with a temperature profile close to the ideal of instantaneous heating, consequently reducing the lethality contribution from the heating step. The results show the importance of modeling and simulation in process analysis. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.