Novel alkali extraction, optimisation, characterisation, and antioxidant activity of polysaccharides from Foshou yam

Foshou yam (Dioscorea opposita Thunb.), cultivated as a vegetable in the region of eastern Hubei Province, China, is a nutritious delicacy. Polysaccharides in the genus Dioscorea play important roles in health-promoting activities. Previous extraction methods used to obtain polysaccharides from Foshou yam (FYP) included water and enzymes, but not alkali conditions. The extraction methods greatly influenced the structure and biological properties of polysaccharides. Hence, in the present work, the alkali extraction of FYP was explored and optimised using the response surface method. The characterisation and antioxidant activity of FYP were also investigated. The results showed that the optimal extraction conditions were as follows: sodium hydroxide concentration, 1.0 mol/L; extraction time, 8 h; and solvent-to-material ratio, 10 mL/g. Under these conditions, the FYP extraction yield was 64.52 ± 0.23%. FYP contained 91.70% of the total sugar with a minimal amount of protein. FT-IR analysis revealed the presence of α-D-glucopyranose in FYP. Congo Red tests indicated that the triple helical conformation in FYP did not exist. In addition, in vitro antioxidant activity experiments revealed that FYP exhibited good scavenging capacity on DPPH and superoxide anion free radicals. These results indicated that the FYP can be used as a novel natural antioxidant in the functional food industries.