The HG domain is the key factor responsible for antioxidant activity of pectin polysaccharides from Polygonum aviculare L.

In this study, we purified two pectin macromolecules designated as WPAP-Aa (59.9 kDa) and WPAP-Ab (83.8 kDa) from Polygonum aviculare L. by using hot water extraction, ethanol precipitation and chromatographic purification. Through enzymatic hydrolysis together with methylation analysis, FT-IR and NMR analysis, WPAP-Aa and WPAP-Ab are confirmed to be composed of rhamnogalacturonan I (RG-I), rhamnogalacturonan II (RG-II) and homogalacturonan (HG) domains with mass ratios of 2.8:1:12.9 and 2.5:1:3. The RG-I domains are substituted with α-L-1,5-arabinan and type II arabinogalactan (AG-II) side chains, as well as minor contributions of β-D-1,4-galactan side chains. The HG domain was released as un-esterified oligogalacturonides with 1–3 degrees of polymerization following de-esterification and endo-polygalacturonase degradation. WPAP-Aa and WPAP-Ab elicit relatively strong antioxidant activities in vitro, which in part might be due to the presence of a high content of galacturonic acid (GalA). The current findings elucidate structural characteristics of pectic polysaccharides isolated from Polygonum aviculare L., laying the groundwork for subsequent exploration of their bioactivity-correlated molecular architectures.