Abstract:Ultrasonic treatment has been widely used to increase the yield during extraction of polysaccharides from longan pulp; however, its effect on the bioactivity of polysaccharides remains unclear. Polysaccharides from dried (LPD) and fresh longan pulp (LPF) were treated with ultrasonic waves at different power settings. Resulting molecular weight distribution as analyzed by gel chromatography indicated significant changes after ultrasonic treatment at 150~450 W for 15 min, partly due to degradation of their high molecular weight fractions. This degradation was confirmed by a decrease in intrinsic viscosity following an increase in the power of ultrasonic waves from 150 to 450 W. The effects of different power values on molecular weight distribution showed no obvious difference. Additionally, the ultrasonic treatment resulted in the cleavage of O-glycosidic bonds in LPD and the dissociation of non O-glycosidic bond-bound protein in the high-molecular weight fraction of LPF. In vitro immunomodulatory evaluation showed that LPD and LPF (50~400 μg/mL)-mediated stimulation of splenic lymphocyte proliferation, macrophage phagocytosis, and NO production were weakened to various degrees after ultrasonic treatment, which might be related to macromolecule degradation and dissociation of bound proteins. Moreover, ConA-induced lymphocyte proliferation by LPD at 400 μg/mL was significantly increased after ultrasonic treatment (p < 0.05), which might be due to the decrease in viscosity. The results suggest that the degradation of polysaccharides from longan pulp due to ultrasonic treatment leads to a significant reduction in immunomodulatory activity in vitro.
