Purification and fine structural analysis of pectic polysacchrides from Osmunda japonica Thunb

• Two pectic fractions were purified from Osmunda japonica Thunb polysaccharides . • WOJP-A-b was a pectic polysaccharide rich in homogalacturonan (HG) regions. • WOJP-A-c was a pectic polysaccharide rich in HG and rhamnogalacturonan I domains. • Osmunda japonica Thunb could provide natural pectin products for functional foods. Osmunda japonica Thunb, as a traditional edible wild herb in China, has a wide range of pharmacological effects. In this study, two pectic polysaccharides, WOJP-A-b and WOJP-A-c, were obtained from O. japonica stalks by water extraction and alcohol precipitation method, and their fine structures were investigated. Monosaccharide composition and molecular weight analyses showed that WOJP-A-b (10.6 kDa) was mainly composed of galacturonic acid (GalA), with less galactose (Gal) and arabinose (Ara) (molar ratio = 68.3: 12.5: 9.0), while WOJP-A-c (6.6 kDa) was primarily composed of GalA, Gal, Ara, and rhamnose (Rha) residues in a molar ratio of 39.4: 41.2: 11.8: 6.8. The results indicated that WOJP-A-b consisted of esterified homogalacturonan (HG) domains, while WOJP-A-c contained HG domains, as well as 1,4- β -galactan and 1,5- α -arabinan, which might be linked covalently to the minor rhamnogalacturonan I (RG-I) domains. The results of this study will provide the basis for structure-activity relationship studies of O. japonica polysaccharides and development of natural functional foods and pharmaceuticals. Acidic polysaccharides (WOJP-A) were obtained from Osmunda japonica Thunb by extraction and isolation, and the major acidic polysaccharide fractions WOJP-A-b and WOJP-A-c were further obtained by isolation and purification, and then both were structurally analyzed, and finally deduced WOJP-A-b consisted of esterified homogalacturonan (HG) domains, while WOJP-A-c contained HG domains, as well as 1,4- β -galactan and 1,5- α -arabinan, which might be linked covalently to the minor rhamnogalacturonan I (RG-I) domains.