Antioxidant activity and phenolic contents of asparagus juice affected by the treatment of pectolytic enzyme preparations.
The antioxidant activity of asparagus (Asparagus officinalis L.) ranks high among the commonly consumed vegetables. Effects of commercial pectolytic enzyme preparations on the rutin content and antioxidant activity of asparagus juice were investigated. The antioxidant activity of asparagus juice was determined using the DPPH (2,2'-diphenyl-l-picrylhydrazyl) method. Seven of the eight commercial pectolytic enzyme preparations showed various rutinase activities and Viscozyme contained the greatest rutinase activity. Rutinase can hydrolyze the glycoside of rutin to form quercetin. Although quercetin has greater antioxidant activity than rutin as determined by DPPH method, the antioxidant activity of asparagus juice treated with Viscozyme was not significantly increased. A pectinase from Aspergillus niger (pectinase AN) decreased rutin content and antioxidant activity of asparagus juice markedly, which was probably due to peroxidase existing in pectinase AN. The pH of asparagus juice, incubation temperature and amount of pectinase AN added to asparagus juice affected the rate of rutin loss in asparagus juice. For pectinase AN, rutin loss in asparagus juice was greater at pH 5.8 and pH 4.5 than that at pH 3.2. Rhamnosidase was identified in pectinase AN. Rhamnosidase can hydrolyze the rhamnose in rutin to produce quercetin-3-glucoside. Quercetin-3-glucoside has greater antioxidant activity than rutin as determined by DPPH method. Heating of pectinase AN at 70