维生素C诱发自由基降低天然产物来源多糖黏度的多组分互相作用分子机制

Understanding of the interactions between chemical components in foods (intermolecular association, aggregation, degradation, etc) and the mechanisms helps clarify food quality and function, which depends on characteristics of multi-scale structure. Vitamin C is a kind of small molecules commonly used and found in food. It has great influence on polysaccharide viscosity and other properties, while has not received much attention. This project aims at systematically analyzing effects of vitamin C on the rheological, structural and conformational properties of viscous polysaccharides from natural resources, by applying modern analytical techniques combined with free radical theory. Various polysaccharides will be used in the study, including pectin, konjac glucomannan, high viscous β-glucan and arabinoxylan, etc. More importantly, the mechanism of free radical induced degradation of polysaccharides mediated by vitamin C, the degradation pathway of vitamin C, and interactions between specific degraded products from vitamin C and the polysaccharides will be elucidated, based on the polysaccharide structure. The investigation may help explain how vitamin C significantly reduces the viscosity of natural polysaccharides, and understand the law of vitamin C induced free radical based on the structural characteristics of polysaccharide in the degradation process. Therefore, the molecular mechanism of interactions between vitamin C and the viscous polysaccharides from natural polysaccharide will be clear. Results of this project would enrich the theory of multi-components interactions in complex food system, and provide great theoretical support for the development of food rich in polysaccharides.

明晰食品中组分间相互作用（分子间缔合、聚集、降解等）及相关机制，有助于阐明基于多尺度结构特性的食品品质与功能。维生素C作为食品中常见的一类小分子，对食品中多糖的黏度等功能性质有重要影响，但没有得到广泛重视。本项目拟利用现代仪器分析技术和自由基理论，系统性地分析维生素C对天然产物来源高黏性多糖（果胶、魔芋葡甘露聚糖、高黏性β-葡聚糖、阿拉伯木聚糖等）的流变行为、结构及空间构象特征的影响，尤其是在此过程中基于多糖结构基础的维生素C介导自由基降解多糖的机制、维生素C降解途径以及特定降解产物与多糖间相互作用。通过上述研究，阐明维生素C通过何种方式显著降低天然产物来源多糖黏性及在此过程中基于多糖结构特征的维生素C诱发自由基规律，明确维生素C与天然产物来源高黏性多糖相互作用的分子机制。相关成果将丰富食品复杂体系中多组分相互作用理论，为开发富含多糖食品提供有力的理论支持。

维生素C与多糖均广泛存在于食品体系中，而低浓度维生素C会导致多糖黏度下降，因此阐明维生素C对多糖黏度降低的影响机制具有很好的科学意义。本课题系统性阐明了不同条件（Vc浓度、反应温度、时间、pH、金属离子等）下Vc对4种不同结构特征的天然产物来源多糖（阿拉伯木聚糖、果胶多糖、葡甘露聚糖、β-葡聚糖）表观黏度的影响，发现低浓度、弱酸性条件下的Vc更容易引起多糖黏度下降，适当升高反应温度、延长加热时间或添加过渡金属Cu2+/Fe2+都能够促进多糖黏度的降低；在此基础上分别比较Vc处理前后多糖的结构特征和溶液构象，明确Vc处理后多糖分子量明显降低，溶液构象参数也发生了变化；其中秋葵果胶多糖的甲基酯化度和乙酰化度有着显著增加，推测OPP中未被甲酯化或乙酰化的半乳糖醛酸可能是Vc的作用位点；但单糖组成、红外光谱、糖苷键连接方式以及NMR信号均无明显变化，因此Vc对多糖的结构影响采用常规的结构表征手段难以捕捉到。利用电子自旋共振光谱技术分析反应体系内自由基的生成变化规律，将多糖溶液黏度的降低与•OH的生成水平进行关联，揭示Vc能够引发体系内•OH的形成，从而导致溶液黏度和分子量降低。此外，通过监测反应过程中Vc的含量变化进一步佐证Vc发生了降解反应，而添加小分子化合物（如蔗糖、苯丙氨酸和半胱氨酸）能够抑制自由基反应从而减缓多糖黏度的降低。通过本研究，将“流变行为、结构特征与自由基监测”相结合，阐述维生素C与多糖的反应机制，为今后开发高黏性多糖与维生素C相互共存的食品（实现黏度有效调控等）提供理论依据，同时为研究小分子与多糖的相互作用提供理论依据和数据参考。

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