ObjectiveIn order to provide scientific basis for development and utilization of larch bark, we investigated the degradation conditions of polymeric proanthocyanidin from larch bark catalyzed by resin and antioxidant activity of degradation products.

MethodLarch bark oligomeric proanthocyanidins (LOPC) was prepared from polymeric proanthocyanidins of larch bark (LPPC) by CR57 resin catalytic degradation. Based on single factor experiments and response surface design analysis, the degrading conditions were optimized, and the structure characterization and antioxidant activity of the degradation product were analyzed as well.

ResultThe results showed that the optimum conditions of catalytic degradation were as follows: the catalytic resin dosage 18mL per 100mL LPPC, catalytic temperature 76 ℃, catalytic reaction time 1.8 hours. Under the above conditions, the average degree of polymerization of degradation products was 3.76. Through the comparison of the chromatogram of LPPC and LOPC, it was found that the content of polymeric proanthocyanidins in the degradation products was obviously reduced, thereby proving that LPPC was degraded. The degradation products were characterized by UV and FTIR, and confirmed to have procyanidins features. The molecular mass distribution of the degradation products was analyzed by the linear model of MALDI-TOF mass spectrometry. The results revealed that LOPC was an oligomer with tetramer mainly from trimer to twelve oligomer. The LOPC exhibited a strong antioxidant activity, and its IC₅₀ on DPPH free radical scavenging, ·OH free radical scavenging and ABTS free radical scavenging were 72.56, 12.64 and 2.52mg/L, respectively. Compared with GS, the LOPC on DPPH· scavenging capacity was higher and the reducing capacity, ·OH scavenging capacity and ABTS⁺· scavenging capacity were lower. But the LOPC on these free radical scavenging capacity was higher than PB, VC, TBHQ.

ConclusionIt was concluded that CR57 resin could be used to catalyze the degradation reaction of LPPC, and the degradation product LOPC had good antioxidant activity.