Combined effects of aqueous chlorine dioxide and ultrasonic treatments on shelf-life and nutritional quality of bok choy (Brassica chinensis)

Abstract

The combined effects of aqueous chlorine dioxide (ClO2) and ultrasonic treatment on the shelf-life, some nutrients and bioactive compounds of bok choy were investigated. Minimally processed bok choy was treated in 50 ppm aqueous ClO2 solution subjected to 80 kHz frequency ultrasound at 0, 120, 150, 180, and 210 W for 10 min. Aqueous ClO2 plus ultrasound treatments significantly (p < 0.05) reduced total bacterial counts by up to 2.8 log CFU/g and Pseudomonas spp. by up to 2.5 log CFU/g, respectively, on day 0, and inhibited their growth on bok choy throughout the 12 d storage period at 4 °C. Among the treatments studied, aqueous ClO2 plus 180 W-ultrasound treatment demonstrated maximum reduction of microbial loads and minimum impact on visual quality (L*, a*, and b* values), chlorophyll degradation, membrane permeability, ascorbic acid and total phenolic contents. In addition, the combined treatment significantly (p < 0.05) inhibited the activities of polyphenol oxidase and polyphenol peroxidase and increased the activity of phenylalanine ammonia lyase as compared with controls. These results indicated that aqueous ClO2 plus ultrasonic treatments is an effective approach for maintaining some nutrients and bioactive compounds, as well as extending the shelf-life of fresh bok choy.