Effect of microwave pretreatments on browning properties of apple juice

In order to investigate the relationship between microwave combined with three anti-browning agentswhey protein isolates (WPI) , ascorbic acid (AA) , citric acid (CA) pretreatment of raw apple and browning of apple juice, the effects of different microwave power and time treatment on the browning of apple juice during apple juice processing were studied. The results indicated that apple juice had lower activity of PPO and higher color value with the increase of microwave power and time, with the microwave power of 720W and time of 120s, the activity of polyphenol oxidase were almost inhibited, color value and the content of total phenolics and amino-nitrogen were increased, total sugar content were reduced and total acid content were increasing slightly. Among those pretreatments, microwave-WPI was the most appropriate way to inhibit browning because of the color value of apple juice was 91.14 which was comparable with others and total phenolics content had the least increase.