Extraction optimization, physicochemical property, antioxidant activity, and α‐glucosidase inhibitory effect of polysaccharides from lotus seedpods

Lotus seedpods are an agricultural by-product of lotus (Nelumbo nucifera Gaertn.), which is widely cultivated in Southeast Asia and Australia. Most lotus seedpods are considered waste and are abandoned or incinerated, resulting in significant waste of resources and heavy environmental pollution. For recycling lotus seedpods, the extraction optimization, physicochemical properties, antioxidant activity, and α-glucosidase inhibitory effect of the polysaccharides contained therein were investigated in this study.Hot water extraction of lotus seedpod polysaccharides was optimized by using a response surface methodology combined with a Box-Behnken design, with the optimum conditions being as follows: a liquid/solid ratio of 25.0 mL g-1 , an extraction temperature of 98.0 °C, and an extraction time of 138.0 min. Under these conditions, an experimental yield of 5.88 ± 0.06% was obtained. Physicochemical analyses suggested that lotus seedpod polysaccharides belong to acidic heteropolysaccharides and are principally composed of rhamnose, arabinose, galactose, glucose, mannose, and galacturonic acid. The polysaccharides content has a broad molecular weight distribution (2.15 × 105 to 1.77 × 107 Da), an α-configuration, and mainly possesses smooth and sheet-like structures. Biological evaluations showed that the polysaccharides possessed good scavenging activity on 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, 1,1-diphenyl-2-picryl-hydrozyl, and hydroxyl radicals, and exerted an obvious inhibitory effect on α-glucosidase activity. Moreover, the polysaccharides content was determined to be a mixed-type noncompetitive inhibitor of α-glucosidase.The results indicate that lotus seedpod polysaccharides have potential as natural antioxidants and hypoglycaemic substitutes. This study provides the theoretical bases for the exploitation and application of polysaccharides from lotus seedpod by-product resources. © 2022 Society of Chemical Industry.