Structural characterization and antioxidant activities of polysaccharides from okra (Abelmoschus esculentus (L.) Moench) pericarp

In this study, okra ( Abelmoschus esculentus  (Linn.) Moench) pods (pericarp) obtained after removing seeds and flesh were applied for polysaccharide extraction. The 60 °C water extract polysaccharide (OPW-60) was obtained from okra peel at 60 °C, and then 100 °C water extract polysaccharide (OPW-100) was obtained from the residue at 100 °C. Acid extraction at 60 °C was finally used to obtain the polysaccharide by acid leaching at 60 °C (OPA-60). Then, structural characteristics and antioxidant activities investigations were performed on the extracted polysaccharides. The results showed that monosaccharide composition of three polysaccharides was different. OPW-60 was mainly type I rhamnogalacturonan (RG-I) pectin, while OPW-100 and OPA-60 consist of RG-I and homogalacturoan (HG) pectins. 1 H NMR analysis confirmed the existence of rhamnose and acetyl group among them. The structure diversity resulted in the difference of viscosity, molecular weight, surface morphology and antioxidant activities. OPW-60 exhibited the highest apparent viscosity, which might be attributed to the differences in molecular weight distribution and monosaccharide composition. OPW-60 was most effective in scavenging 2,2-Diphenyl-1-picrylhydrazyl radicals and chelating ferrous ion ability, while OPW-100 exhibited the highest hydroxyl radical scavenging activity. The results showed that polysaccharides with different structure and antioxidant ability could be obtained from okra under different extraction conditions.