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

Abstract

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. 1H 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.