Abstract: In order to produce in large scale oligomeric procyanidins (OPC) (with polymerization degree (DP) less than 5) that can be absorbed by the body, we studied the effects of NaOH pretreatment on the depolymerization of grape seed procyanidins (PC) and the antioxidant activity in vitro of OPC. The effects of different pretreatment temperatures (40, 60, and 80 ℃), times (15, 30, and 60 min) and NaOH concentrations (0, 1, 2, 4, 6, 8, 10, 15, 20, and 25 mol/L) on the mean degree of polymerization (mDP) of PC, and the composition and content as well as antioxidant activity in vitro of OPC. The results showed that the optimum conditions for generating OPC were as follows: NaOH concentration 10 mol/L and pretreatment at 60 ℃ for 15 min. Compared with the control (pretreated with 0 mol/L NaOH at 60 ℃ for 15 min), the optimized NaOH pretreatment reduced the mDP of PC from 5.39 ± 0.12 to 1.30 ± 0.014, increased the total area of OPC by 8.28 times and OPC content by 6.42 times, and enhanced in vitro scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl hydrate (DPPH) and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) radicals and ferric reducing antioxidant power (FRAP) by 4.22, 5.13 and 3.84 times, respectively. In summary, this study provides a novel way of producing OPC, which could facilitate the high value-added utilization of grape seeds.

Key words: grape seeds, procyanidins, depolymerization, oligomeric procyanidins, antioxidant activity