Effects of extraction methods on the physicochemical characteristics and biological activities of polysaccharides from okra (Abelmoschus esculentus)

The impacts of three extraction techniques, including hot water extraction (HWE), pressurized water extraction (PWE), and microwave assisted extraction (MAE), on the physicochemical characteristics, antioxidant activities, in vitro binding properties, and in vitro inhibitory activities on α-amylase and α-glucosidase of okra polysaccharides (OPPs) were investigated and compared. The extraction yields, constituent monosaccharides, and FT-IR spectra of OPP-W, OPP-P, and OPP-M extracted by HWE, PWE, and MAE, respectively, were similar. However, their molecular weights, intrinsic viscosities, uronic acids, and degree of esterification were different. Furthermore, results showed that OPP-W, OPP-P, and OPP-M exhibited remarkable antioxidant activities, binding capacities, and inhibitory activities on α-amylase and α-glucosidase. Indeed, the antioxidant activities of OPP-W were significantly lower than those of OPP-M and OPP-P, which might be attributed to the low molecular weights and high contents of unmethylated galacturonic acid of OPP-P and OPP-M. However, the binding capacities and inhibitory activities on α-amylase and α-glucosidase of OPP-W and OPP-P were similar, but significantly higher than those of OPP-M, which might be attributed to the low molecular weights of OPP-M. Results suggested that the PWE method could be a good potential technique for the extraction of OPPs with high bioactivities for industrial applications.