龙眼是一种颇受欢迎的亚热带水果，其干制果肉作为传统中药材亦被人们所熟知，而多糖是主要的生物活性成分。基于多糖理化特征和免疫调节活性的分析评价，探析新鲜和干制龙眼果肉的营养性差异。通过气质联用、离子交换层析、凝胶过滤层析、粘度测定、紫外和红外光谱分析发现，新鲜果肉多糖（LPF）和干制果肉多糖（LPD）均为多糖-蛋白络合物，但两者的结合蛋白含量、中性与酸性多糖含量比、单糖组成、分子量分布和特征粘度均存在显著差异。体外细胞试验证实，LPD在50–400 μg/mL剂量范围内对脾淋巴细胞增殖和巨噬细胞吞噬的增强作用明显强于LPF。LPD和LPF均能显著刺激ConA诱导的脾淋巴细胞增殖和巨噬细胞NO生成(P<0.05)，但对LPS诱导的脾淋巴细胞增殖刺激作用较弱。龙眼果肉的干制处理可能通过改变水溶性多糖的理化特征而增强其体外免疫调节活性。

Longan is a popular fruit and is widely distributed throughout the subtropical area. The dried pulp of longan has been used in traditional Chinese medicine and is made up of polysaccharides as one of the main bioactive ingredients. The nutritional difference between fresh and dried longan pulp products was investigated using analytical methods and the physicochemical properties and immunomodulatory activity of polysaccharides were evaluated. Gas chromatography-mass spectrometry (GC-MS), ion exchange chromatography, gel filtration chromatography, viscometry, ultraviolet (UV) spectroscopy, and infrared (IR) spectroscopy were performed. The results showed that the longan polysaccharides from fresh and dried fruits (i.e., LPF and LPD, respectively) were polysaccharide-protein complexes, but significant differences were found in their binding protein contents, neutral/acid polysaccharide ratios, monosaccharide compositions, molecular weight distributions, and intrinsic viscosities. Cellular in vitro tests confirmed LPD strongly stimulated lymphocyte proliferation and macrophage phagocytosis compared to LPF in the dose range of 50~400 μg/mL. Both polysaccharides significantly stimulated ConA-induced lymphocyte proliferation and nitric oxide production from macrophages (P < 0.05), but had a weak effect on lipopolysaccharide (LPS)-induced lymphocyte proliferation. The drying process of longan pulp may enhance the in vitro immunomodulatory activity of water-soluble polysaccharides by changing their physicochemical characteristics.

国家自然科学基金资助项目（31301416）