Pectic polysaccharides from Lilium brownii and Polygonatum odoratum exhibit significant antioxidant effects in vitro

Two pectic polysaccharides (WLBP-A3-c and WPOP-A-c) were isolated from traditional Chinese medicines Lilium brownii and Polygonatum odoratum, respectively. Monosaccharide composition, FT-IR, NMR and enzymatic analyses indicated that both WLBP-A3-c (59 kDa) and WPOP-A-c (33 kDa) contained homogalacturonan (HG), rhamnogalacturonan I (RG-I), and rhamnogalacturonan II (RG-II) domains, with mass ratios of 76.0: 17.2:6.8 and 76.8:10.6:12.6, respectively. Two RG-I domains WLBP-A3-c-DE1 and WPOP-A-c-DE1, correspondingly obtained from WLBP-A3-c and WPOP-A-c by enzymatic hydrolysis, were composed of repeating units of [→2)-α-L-Rhap-(1 → 4)-α-D-GalpA-(1→] with highly branched neutral sugar side chains at the O-4 position of Rhap, which contained arabinan, galactan, arabinogalactan I and II (AG-I and AG-II) side chains in different proportions. By comparison, WPOP-A-c exhibited higher scavenging effects against DPPH, ABTS and hydroxy radicals than WLBP-A3-c, probably because WPOP-A-c had higher contents of GalA residues and HG domains and lower molecular weight. Among three domains of WPOP-A-c, HG domain possessed the strongest activity in decreasing ROS production and promoting SOD activity, resulting in the effective protection of HepG2 cells against H₂O₂-induced oxidative stress. Our study provides evidence that pectins rich in HG domains from Lilium brownii and Polygonatum odoratum exhibit significant antioxidant effects, which hold potential for the application in the field of healthcare products.