Physicochemical characterization and in vitro biological activities of polysaccharides from alfalfa (Medicago sativa L.) as affected by different drying methods

Abstract

Alfalfa (Medicago sativa L.) polysaccharides (MSPs) were subjected to three drying methods, namely, hot-air drying (HD), freeze drying (FD), and vacuum drying (VD). Three corresponding polysaccharides were obtained and named HD-MSPs, FD-MSPs, and VD-MSPs. The physicochemical characteristics and activities of the three MSPs were compared. The results showed that the three MSPs all consisted of five monosaccharides: glucuronic acid, rhamnose, glucose, galactose, and xylose. However, the glucuronic acid contents of HD-MSPs (7.90 %) and VD-MSPs (9.94 %) were lower than that of FD-MSPs (11.65 %). HD-MSPs and VD-MSPs had higher molecular weights than that of FD-MSPs. HD-MSPs possessed higher inhibition activities against α-amylase and α-glucosidase than VD-MSPs and FD-MSPs, which might be due to their relatively higher viscosities and molecular weights. The scavenging activities of FD-MSPs for 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and 2,2-azino-bis-(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) radicals were the highest among those of the three MSPs, which might be related to their lower molecular weight and higher content of uronic acid. These results suggested that MSPs obtained by different drying methods possessed different specific characteristics and had the potential to be used for different purposes, where HD-MSPs and FD-MSPs had the potential to be used as a hypoglycemic agent and an antioxidant, respectively.