超声波广泛用于龙眼果肉多糖的浸提以实现提取率的大幅增加，但对其生物活性的影响尚不清楚。采用不同功率超声处理干制和新鲜龙眼果肉粗多糖（LPD和LPF），以凝胶色谱法分析分子量分布发现：经150-450 W超声处理15 min后，因高分子量级分降解，LPD和LPF的分子量分布发生明显变化，且其降解行为也由逐渐减小的特征粘度所印证，而不同功率之间的影响差异不明显。超声处理还能解离LPD中大部分O型糖苷键以及LPF高分子量级分中非O型糖苷键结合的蛋白。体外免疫调节活性评价发现：超声处理不同程度地减弱LPD和LPF（50~400 μg/mL）对脾淋巴细胞增殖、巨噬细胞吞噬和NO生成的刺激活性，可能源于高分子降解和结合蛋白解离；LPD经超声降解后在400 μg/mL剂量下对ConA诱导淋巴细胞增殖的刺激活性显著增强（p<0.05），推测与粘度降低有关。超声波对龙眼多糖分子的降解作用导致其体外免疫调节活性明显减弱。

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.

国家自然科学基金资助项目（31301416）