Effect of heat and pH on the radical-scavenging activity of proanthocyanidin-rich extract from grape seeds and production of Konjac enriched with proanthocyanidin

The effects of heat and pH on the radical-scavenging activity of proanthocy anidins, oligomeric and polymeric polyhydroxyflavan-3-ol units, and ascorbi c acid were compared. The radical-scavenging activity was evaluated by meas uring the decrease of 1,1-diphenyl-2-picrvlhydrazyl (DPPH) detected at 517 nm. Proanthocyanidin-rich extract from grape seeds (GSE) had stronger radic al-scavenging activity than ascorbic acid and (+)-catechin, which is the mo nomeric compound of proanthocyanidin. This result suggested that more pheno lic OH groups in a molecule caused stronger DPPH radical-scavenging activit y. GSE was more stable against heat and pH than ascorbic acid. In acidic re gion, pH 4.0, the DPPH radical-scavenging activity of GSE almost possessed at 100 degreesC for 5 hours, while that of ascorbic acid decreased less tha n 10%. In neutral region, pH 7.0, the activity of GSE was stable less than 50 degreesC for 5 hours. In alkaline region, pH 10.0, 60% of activity of GS E remained at 100 degreesC for 30 min, although the activity of ascorbic ac id were completely lost. As it was clear that GSE was suitable for food ing redient of food processing and cooking, GSE was adapted to Konjac productio n, which is necessary for alkaline treatment. Konjac enriched with GSE sign ificantly showed the DPPH radical-scavenging activity.