Abstract: The composition, Fourier transform infrared (FTIR) spectral characteristics and molecular mass distribution of crude polysaccharides extracted from fresh, hot air, vacuum, infrared and freeze-dried longan (Dimocarpus longan Lour.) pulp, named as FLP, HDLP, VDLP, IDLP and FDLP, respectively were analyzed, and their antioxidant activity and immune-stimulating activity were evaluated as well as their stability in simulated digestive system. The five crude polysaccharides mainly contained glucans and proteins at different mass fractions, and were distinct in amino acid composition. In addition, they exhibited significant differences in molecular mass distribution with average molecular mass ratio of 51.37:28.33:5.95:7.86:1.00, but not in the polysaccharide and protein (in the amide region) infrared absorption characteristics. Comprehensive comparison showed that FDLP had stronger scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radicals, while HDLP had a stronger ability to stimulate macrophages to generate NO and tumor necrosis factor-α. Longan polysaccharides were relatively stable in simulated intestinal juice, but degraded in simulated saliva and gastric juice, releasing a small amount of reducing sugar dominated by glucose, while the digestion performance of IDLP was different from the other four polysaccharides. From this study, we conclude that drying methods affect the physicochemical and biochemical properties of polysaccharides extracted from dried longan pulp. Selecting an appropriate drying method is vital for controlling the functional quality of dried longan pulp.

Key words: longan, polysaccharide, physicochemical characteristics, activity, digestion