Moderate vacuum packing and low temperature effects on qualities of harvested mung bean (Vigna radiata L.) sprouts

Post-harvest browning, decay, lignification, and other adverse physiological effects limit the shelf-life of mung bean sprouts at ambient temperature. In this study, vacuum packing at pressures of 0, ↓0.02, ↓0.04, and ↓0.06 mPa at 20 °C, and the optimum pressure of ↓0.04 mPa at 4 °C for maintenance of sprouts, was investigated. Chlorogenic acid was identified as the main phenolic compound leading to the browning of mung bean sprouts, along with total flavonoids, total phenols, rutin, and o-phthalic acid. Among these, flavonoids were identified as being the main substrate for polyphenol oxidase (PPO) activity. Moderate vacuum packing combined with low temperature storage inhibited PPO, as well as peroxidase (POD) and superoxide dismutase activities, which was associated with a slower rate of browning. In addition, these storage conditions reduced the activity of phenylalanine ammonia lyase (PAL), thereby suppressing the synthesis of phenolic substrates used in the browning reaction. Moderate vacuum packing combined with low temperature storage also maintained the activities of the cell wall-degrading enzymes cellulase and xylanase, and suppressed POD and PAL activities. Together, these effects would be expected to lead to a decrease in cellulose, hemicellulose, and lignin levels, ultimately restricting sprout elongation and maintaining the firmness of the sprouts.