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

摘要

The effects of heat and pH on the radical-scavenging activity of proanthocyanidins, oligomeric and polymeric polyhydroxyflavan-3-ol units, and ascorbic acid were compared. The radical-scavenging activity was evaluated by measuring the decrease of 1,1-diphenyl-2-picrvlhydrazyl (DPPH) detected at 517 nm. Proanthocyanidin-rich extract from grape seeds (GSE) had stronger radical-scavenging activity than ascorbic acid and (+)-catechin, which is the monomeric compound of proanthocyanidin. This result suggested that more phenolic OH groups in a molecule caused stronger DPPH radical-scavenging activity. GSE was more stable against heat and pH than ascorbic acid. In acidic region, 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 than 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 GSE remained at 100 degreesC for 30 min, although the activity of ascorbic acid were completely lost. As it was clear that GSE was suitable for food ingredient of food processing and cooking, GSE was adapted to Konjac production, which is necessary for alkaline treatment. Konjac enriched with GSE significantly showed the DPPH radical-scavenging activity.