Elucidating the structure–antioxidant activity relationship of pectins from Agastache rugosa (Fisch. & C.A.Mey.) Kuntze

This study systematically investigates the structural characteristics and antioxidant activities of pectic polysaccharides extracted and purified from Agastache rugosa (Fisch. & C.A.Mey.) Kuntze. Through sequential purification involving ion-exchange and gel permeation chromatography, two homogeneous pectin fractions-WARP-A2b (17.5 kDa) and WARP-A3b (51.5 kDa)-were obtained. Their structural domains, including homogalacturonan, rhamnogalacturonan I, and rhamnogalacturonan II, were characterised using FT-IR, NMR, Congo red binding, circular dichroism, and SEM. Monosaccharide composition analysis revealed both fractions to be rich in galacturonic acid, rhamnose, galactose, and arabinose. WARP-A3b exhibited stronger antioxidant capacity in scavenging ABTS, DPPH, and hydroxyl radicals, which may be attributed to its higher galacturonic acid content and distinct rhamnogalacturonan-I domain organisation. Enzymatic hydrolysis and de-esterification experiments further elucidated the contribution of specific structural domains to antioxidant performance. These results offer new insights into the structure-activity relationships of A. rugosa pectins and support their potential as natural antioxidants in pharmaceuticals.