Effect of 6-Benzylaminopurine Combined With Ultrasound as Pre-Treatment on Quality and Enzyme Activity of Green Asparagus

Green asparagus (Asparagus officinalis L.) was harvested and treated by immersion in 20 µg/g 6-benzylaminopurine (6-BAP) and submitted to ultrasound wave (20 kHz) for 20 min, then stored at 12 ± 2C for 10 days, followed by 10 days at 2 ± 2C. The changes in quality and enzyme activities of asparagus were investigated. Qualities such as chlorophyll content, shear force, lignin and crude fiber contents were monitored during storage. Similarly, the increases in shear force and lignin following ultrasound-assisted 6-BAP treatment were significantly reduced (P < 0.05) during the first 10 days, crude fiber contents appeared significantly reduced (P < 0.05) after 20 days. The enzyme activities of asparagus including catalase, polyphenol oxidase, ascorbate peroxidase were also enhanced by treatments with 6-BAP; phenylalanine ammonia lyase was relatively inhibited, and peroxidase was promoted within 5 days and subsequently inhibited. Ultrasound wave treatment appeared to enhance the effect of 6-BAP on asparagus. PRACTICAL APPLICATIONS Besides cleaning of fresh-cut vegetables and fruits for its removal of dirt and bacteria without mechanical damage, ultrasonic sound can be used as a pretreatment to enhance the effects of preservative on postharvest fruit and vegetable. It can be used in a farm or a supermarket after vegetable and fruit harvest.