Physicochemical properties and biological activities of polysaccharides from the peel of Dioscorea opposita Thunb. extracted by four different methods

Polysaccharides are the important biologically active components found in the peel of Dioscorea opposita Thunb. (DTTP). The influences of 4 extraction methods, namely hot water extraction (W), acidic extraction (HA), hot-compressed water extraction (HCW) and enzyme-assisted extraction (EAE), on the yields, physicochemical properties, hypoglycemic and antioxidant activities of polysaccharides from DTTP were studied and compared. Among these DTTP polysaccharides, DTTP-HA was outstanding in several respects. DTTP-HA was the most water soluble; it had the highest total carbohydrate content (85.08 %), the highest uronic acid (13.20 %) and the highest thermal stability. DTTP-HA and DTTP-W possessed a triple-helix structure. These 4 kinds of polysaccharides have the same types of monosaccharides, but in different molar percentages. Extraction method had a significant impact on the microstructures of the extracted polysaccharides. DTT-HA exhibited irregular structure with many holes. Among the 4 extracted methods, the DTTP-HA and DTTP-W initially exhibited higher hypoglycemic and antioxidant activities. The better bioactivities of DTTP-HA may be related to the above factors. The findings indicated that acid extraction is an effective method to extract polysaccharides with high biological activities from DTTP.