Inactivation of polyphenol oxidase by microwave and conventional heating: Investigation of thermal and non-thermal effects of focused microwaves

Emerging technologies, such as focused microwave heating of liquid foods, have been studied to reduce quality losses due to the high temperatures of conventional processing. Besides faster heating, microwaves can also have non-thermal effects on inactivation; however, this is a controversial issue. The objective of this study was to compare conventional and focused microwave heating under similar conditions for the inactivation of two polyphenol oxidases (PPOs): mushroom tyrosinase in buffer and the PPO present in coconut water. Small samples under stirring were treated at temperatures between 50 and 90 degrees C and three kinetic models were adjusted considering the whole time-temperature history. The Weibull model could best describe inactivation in both heating processes, which was more effective with microwave heating for temperatures over 70 degrees C. Validation runs show that the model can satisfactorily describe the PPO inactivation. This study contributes for the design of liquid food pasteurization by focused microwave technology.