Abstract

The physicochemical quality and inactivation of polyphenol oxidase (PPO), peroxidase (POD) in dried longan with high power ultrasonic pretreatment was investigated. Effect of high power ultrasonication was compared with a traditional chemical pretreatment with potassium metabisulfite and non-pretreatment. Chemical qualities, such as a_w, MC, TSS, and TA of the ultrasonic pretreated dried longan samples were significantly lower than those of the control samples (P£0.05), whereas their pH were higher than those of the control samples. Increase in ultrasonication time resulted in decreases of a_w, MC, TSS, and TA, but an increase of pH. The firmness, lightness (L*), and yellowness (b*) values increased and redness (a*) values decreased when the sample was pretreated with increasing ultrasonication time. The application of high power ultrasonic pretreatment for 10, 20, and 30 min could reduce PPO activity by 49.99%, 57.18%, and 70.68%, and POD activity by 47.63%, 86.16%, and 94.06%, respectively. The PPO and POD activities were significantly decreased with increasing ultrasonication time. Panelists were most satisfied with sensory properties of the dried longan with 30 min of high power ultrasonic pretreatment.

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