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Kinetics of destruction of potato polyphenol oxidase (PPO) during vacuum microwave blanching Miladinović, Zoran


Vacuum microwave (VM) blanching decreases enzymatic food browning at low temperatures (between ~40-55°C) when compared to conventional processing methods. The impact and reaction of microwave blanching on polyphenol oxidase (PPO) of the Russet potato was investigated and compared with the effects of conventional convective heating. In order to closely examine PPO kinetics in a microwave field and to establish a PPO assay for use in further investigations, potato puree plus polyvinylpolypyrrolidone (PVPP) was centrifuged and filtered to produce a treatment ready suspension. Whole potatoes were cut into French fry strips and blanched using a pilot-sized V M dehydrator. This was compared to a steam kettle blanch to determine the blanch effects on physical form. Finally, two different microwave treatments were utilized along with a heated water bath in order to compare the microwave heated potato suspension samples with conventional heating. Microwave treatments used a 700 W, 2450 MHz vacuum microwave oven and an Ethos Synth (ES-MR) microwave reactor set at 2450 MHz, which dropped the microwave power level from 700 W to below 100 W after reaching the desired temperature. Experiments in all three treatments were conducted under controlled temperatures between 40°C and 70°C. The decimal reduction values (D-value) of PPO were reduced by heating in vacuum microwave treatments as compared to heating in a water bath at temperatures between 40°C and 57°C. At these temperatures, the D-values, z-values and activation energies (E[sub a]) for the PPO model reaction were significantly lower (p < 0.05) for the VM and the ES than the heated water bath. The results suggest the existence of an alternative inactivation mechanism for PPO when heated in a microwave field compared to a water bath at low processing temperatures.

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