Purification, structural elucidation and physicochemical properties of a polysaccharide from Abelmoschus esculentus L (okra) flowers

Abelmoschus esculentus L (okra) is widely used as a healthy vegetable and favourable source of dietary medicine. Okra flowers which are by-products of okra, are rich in polysaccharide, polyphenols and trace elements etc., however, except a few for health tea, most of them were discarded as the waste of resources. In this study, a polysaccharide named AEFP22 was extracted, purified and identified from okra flowers, and its physicochemical property and antioxidant activity were also elucidated. AEFP22, with a molecular weight of 2.741 x 10(5) Da, was composed of Rha, GalA and Gal in the ratio of 1:1.02:0.86. The methylation and nuclearmagnetic resonance (NMR) analysis indicated AEFP22 was composed of [2)-alpha-D-Rhap-(1 -> 4)-alpha-D-GalpA-(1 -> 2,4)-alpha-D-Rhap-(1 -> 4)-alpha-D-GalpA-(1] with branch of terminal T-alpha-D-Galp pointed at C4 of 1,2,4-alpha-D-Rhap. The Conge-red test, Atomic force microscope ( AFM) and Scanning electron microscope (SEM) further revealed the triple-helical conformation, irregular sheet structure with molecule aggregations of AEFP22. The physicochemical property analysis indicated AEFP22 possessed stable thermal property and exhibited shear-thinning and normal Newtonian fluid in different concentrations, -7.04 mV zeta potential and polymerization phenomenon existed in AEFP22 solution. AEFP22 exhibited good 1,1-diphenyl- 2-picrylhydrazyl (DPPH) radical scavenging ability. These results indicated potential utilization of AEFP22 in nutritional food and material application. (C) 2020 Elsevier B.V. All rights reserved.