Ultrasonic-Assisted Extraction, Structural Characterization, Chain Conformation, and Biological Activities of a Pectic-Polysaccharide from Okra (Abelmoschus esculentus)

The purpose of this study was to better understand the chemical characteristics and chain conformation of okra polysaccharides extracted by ultrasonic-assisted extraction. A pectic-polysaccharide, named OPP-D, was obtained, which was mainly composed of rhamnose, galacturonic acid, and galactose with a molar ratio of 1.01:1.00:2.31. Combined with NMR analysis, -4)-α-d-GalAp-(1,2,4)-α-l-Rhap-(1- were identified as the backbone with galactan side chains substituted partly at O-4 of Rhap. Molecular weight and radius of gyration of OPP-D were determined as 2.19 × 10(5) Da and 27.0 nm, respectively. OPP-D was determined as an air-core sphere with branching chains in 0.9% NaCl solution by high-performance size-exclusion chromatography coupled with multi-angle laser light scattering and dynamic light scattering for the first time. Moreover, OPP-D exhibited typical shear-thinning behavior. In addition, OPP-D exhibited remarkable in vitro antioxidant activities and prebiotic activities, while the relatively high molecular weight, high degree of esterification, high content of uronic acids, and highly branched globular conformation of OPP-D might contribute to its in vitro anti-diabetic activities and binding capacities. Results can contribute to a better understanding of the structure–bioactivity relationship of OPPs, and OPP-D has great potential applications in the functional food and pharmaceutical industries.