关键词: 白三叶, 多糖, 干燥方式, 理化性质, 抗氧化活性

Abstract: This paper reports the results of a comparative study of the effects of three different drying methods (hot air drying, freeze drying and vacuum drying) on the physicochemical properties and antioxidant activity of water-soluble polysaccharides (WSP) from the aerial part of Trifolium repens L. The aim of the study was to find out the best drying method for WSP. The results showed that the yield of freeze-dried polysaccharides was significantly higher than that of hot air-dried and vacuum-dried polysaccharides (P < 0.05). Different drying methods had significant influence on the total sugar and sulfate and uronic acid contents of polysaccharides (P < 0.05) and the total sugar and uronic acid content of dried polysaccharides was in the decreasing order: freeze drying > vacuum drying > hot air drying. On the other hand, the drying methods had no significant effect on the contents of proteins, amino sugars or moisture, pH or relative viscosity of polysaccharides (P > 0.05). The dissolution time of freeze-dried polysaccharides was significantly shorter compared with those dried by two other drying methods (P < 0.05). The polysaccharides from Trifolium repens L. contained a small amount of proteins or polypeptides, and exhibited a triple-helix conformation. The freeze-dried polysaccharides showed stronger reducing power and radical scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl and 2,2’-azino-bis(3- ehtylbenzothiazoline-6-sulfonic acid) free radicals than the two other dried samples (P < 0.05). Therefore, freeze drying was the best drying method for polysaccharides from Trifolium repens L. because it maintained their antioxidant activity.

Key words: Trifolium repens L., polysaccharides, drying methods, physicochemical properties, antioxidant activity