多糖结构和生物活性间的相互关系是影响多糖在食品领域中开发应用的关键科学问题之一。海藻是食品活性多糖的重要来源。泡叶藻聚糖是一种具有强免疫刺激活性的新型海藻多糖，但该多糖分子量大且结构复杂，限制了对其进行深入研究及开发利用。针对该问题，本项目在前期纯化泡叶藻聚糖及深入研究其生物活性的基础上，拟制备泡叶藻聚糖低分子量降解产物，纯化获得具有强免疫活性的低分子量片段，解析其基本结构，并研究硫酸化、磷酸化、乙酰化、羧甲基化等修饰对其免疫刺激活性的影响。本项目的实施预期可明确泡叶藻聚糖的强免疫刺激活性低分子量降解片段的基本结构特征，阐明常见的多糖修饰反应对其免疫刺激活性的影响。这些预期成果不仅可为泡叶藻聚糖的开发和利用提供理论基础，也可为其他海藻多糖的生物活性与结构关系研究提供参考。

The relationships between the structural characteristics and biological activities of polysaccharides are one of key scientific issues in the basic research field of food science, which affect the development and application of polysaccharides in food industry. Seaweeds are important source of polysaccharides with numerous biological activities in food industry. Ascophyllan is a novel sulfated polysaccharide derived from brown alga Ascophyllum nodosum. Our previous studies revealed that ascophyllan possesses potent immunostimulatory activities and seems to be a valuable polysaccharide, which can be developed to functional foods. However, the further development and utilization of ascophyllan is limited due to its large molecule weight (390 kDa) with complex structural characteristics. Based on our previous studies, in this project, we intend to prepare and purify low-molecule-weight degraded fragments with potent immunostimulatory activities (LMWA) from ascophyllan, and clarify the structural characteristics of LMWA. Meanwhile, we aim to reveal the effects of some common chemical modification reactions on the immunostimulatory activities of LMWA, including sulfation, phosphorylation, acetylation, and carboxyl methylation. The implementation of our project will be expected to demonstrate the structural characteristics of LMWA, which possess potent immunostimulatory activities, and further clarify the effects of common modification reactions on the immunostimulatory activities of LMWA. The expected achievements of our study can provide not only the theoretical basis for the development and the application of ascophyllan in food industry, but also some basic information for the study on the structure-activity relationships of other algae polysaccharides.