Effect of Ultrasound Treatment on Quality Maintenance of Fresh-Cut Broccoli

This study aimed to investigate the effect of ultrasound (US) treatment on the quality maintenance of freshcut broccoli during storage. Fresh-cut broccoli was treated ultrasonically at 40 kHz and different power levels (200, 250, 300, 350 and 400 W) for 10 min and then stored at 10 ℃ for up to 96 h. The changes of appearance and microbial load were measured to determine the optimum parameters of US treatment for fresh-cut broccoli. Furthermore, the effect of the optimum US treatment on chlorophyll degradation and the changes in bioactive components in fresh-cut broccoli was studied. The obtained data indicated that US treatments at all power levels tested delayed the increase of yellowing index, L^* value, total mold and yeast count and total bacterial count, and inhibited the decrease of H value, the 300 W power being the most effective in maintaining the appearance and microbial quality of fresh-cut broccoli. US treatment at 300 W effectively inhibited the activities of chlorophyllase and Mg-dechelatase, contributing to maintaining higher contents of chlorophyll a, chlorophyll b and total chlorophyll of fresh-cut broccoli. Meanwhile, this treatment maintained higher contents of bioactive ingredients such as vitamin C, total phenols, total glucosinolates and sulforaphane, and improved the scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radicals. Therefore, these results indicated that US treatment could not only effectively slow down the yellowing of fresh-cut broccoli, but also maintain higher contents of bioactive compounds, thus playing a fresh-keeping role.