Characterization of antioxidant polysaccharides in bitter gourd (Momordica charantia L.) cultivars

Three water-soluble polysaccharides in fruits of bitter gourd (Momordica charantia L.) cultivars, coded as BP1, BP2 and BP3, were isolated by precipitation with alcohol from the aqueous extract of the fruits residue after refluxed with ethanol and deproteined by Sevage method and decolored by 30% H 2 O 2 from the fruit of bitter gourd. Their chemical structure and physicochemical properties were characterized by anthrone-sulfuric acid method, carbazole-sulfuric acid method, FT-IR spectra and gas chromatography, respectively. Furthermore, their antioxidant activities were evaluated by several in vitro systems of assay, namely hydroxyl radical-scavenging activity and superoxide radical-scavenging activity. The results indicated that in the same growing environment, there are differences in monosaccharide composition, structure and antioxidant activities among different bitter gourd cultivars. Three water-soluble polysaccharides of bitter gourd were all composed of L-arabinose (Ara), D-glucose (Glu) and D-galactose (Gal),with variations of the component ratio. All three polysaccharides showed antioxidant activities. They had strong scavenging effect on hydroxyl free radical, and much weaker effect on superoxide radical. Among them, BP1 showed the highest scavenging rate on hydroxyl radicals and superoxide radicals. The presence of polysaccharides with high antioxidant capacity in fruits indicates bitter gourd can be considered an important dietary source of antioxidants.