脂质体系中植物甾醇光敏氧化的分子机制及控制途径研究

Phytosterols in vegetable oils are easy to be oxidized, and transformed into their oxidized forms when subjected to light exposure, which have been proved to be significant cytotoxic, and existing big security risk to human beings. The existed researches were mainly focused on sterol thermal and auto-oxidation, however, their photosensitized oxidation were not been conducted deeply and systematically, especially the effect of unsaturation degree of triglycerides, irradiation light, type of photosensitizer and interface area of lipids to oxygen on photosensitized oxidation behavior of phytosterols has not yet been revealed. In this project, common phytosterols are selected as the research object, and the molecular mechanism and control pathway of their photosensitized oxidation would be explored systematically on the basis of drawing lessons and making innovations from the traditional research ideas. First, the key factor/factors controlling the yield of singlet oxygen in lipid matrix would be explored and confirmed by using singlet oxygen capture and chemiluminescence spectra analytical methodology, and the reaction mechanism of singlet oxygen with sterols would also be further investigated, aiming to reveal the rules that control the transformation and accumulation of different oxidation products. After that, the key elementary reactions that control oxidation rate and the accumulation of oxidation products would be ascertained by means of controlled photosensitized oxidation experiment. On this basis, we will make a further probe into the effect of different antioxidant to blocking oxidation-chain of sterols from the view of quenching singlet oxygen and removing free radicals, etc., and obtain an effective approach to control the oxidation, which would provide theoretical foundation and technical support for edible oil safety.

食用油受到光照后很容易导致植物甾醇的氧化，生成具有显著细胞毒性的氧化产物，存在较大的安全隐患。已有研究主要集中于甾醇的热氧化和自动氧化，对于其光敏氧化尚未开展深入系统研究，特别是基质甘油三酯不饱和度、辐照光源、光敏剂种类、油脂氧接触面等对甾醇光氧化行为的影响尚未探明。因此，本项目以常见植物甾醇为研究对象，在借鉴和发掘传统研究思路的基础上，系统地探索其光敏氧化分子机制及控制途径。首先，借助单线态氧捕获和化学发光光谱分析技术，找到控制脂质体系中单线态氧产率的关键因素，并进一步探究其与甾醇作用的分子机制，揭示氧化过程中不同种类氧化产物转变和累积的规律。然后，通过可控光敏氧化实验，确定控制氧化反应速率和氧化产物累积的关键基元反应。以此为基础，从单线态氧淬灭、游离基清除等多角度出发，探究不同抗氧化方式对甾醇氧化链的阻断效应，获得控制氧化的有效途径，为保障食用油安全提供理论基础和技术支撑。

食用油受到光照后很容易导致植物甾醇（Phytosterols, PS）的氧化，生成具有显著细胞毒性的氧化产物，存在较大的安全隐患。已有研究主要集中于PS的热氧化和自动氧化，对于其光敏氧化尚未开展深入系统研究，特别是基质甘油三酯不饱和度、辐照光源种类和光照强度、光敏剂种类和浓度以及溶氧量等对PS光氧化行为的影响尚未探明。因此，本项目首先对脂质体系中PS光敏氧化的分子机制开展研究，发现1O2是引起PS光氧化的关键因素，其产率与光源种类（波长）、光照强度、光敏剂种类和含量、以及溶氧量等因素存在密切的关系。同等条件下，氙灯促发1O2的产率最高，荧光灯次之、LED灯最弱；在一定范围内，脂质体系中1O2的产率与光照强度、溶氧量和光敏剂浓度呈正比。PS光敏氧化以C5反应路径为主，优势初级产物为α型PS-5-OOH，通过解离机理PS-5α-OOH形成烯丙基自由基-O2对，然后经重排形成PS-7α-OOH，再通过差向异构化转变为PS-7β-OOH，并最终形成典型的植物甾醇氧化物。其次，光源种类和光照强度、光敏剂浓度、脂质体系组成对PS的光氧化特性产生重要的影响。氙灯促发光氧化能力最强，光照处理7 d，PS损失率可达53.84%，生成的甾醇氧化物总量为1525.9 μg/g；同等条件下，PS的氧化劣变和氧化产物的形成与光照强度、光敏剂浓度和脂质体系饱和度呈正相关；甾醇氧化产物的形成主要是通过C5反应路径，以C7位羟基/酮基氧化产物为主，其含量占总氧化产物的2/3以上；在典型脂质体系中PS的降解和POPs的形成均符合一级动力学反应模型。最后，本项目对植物甾醇光敏氧化的抑制开展了深入探索，发现α-生育酚和叔丁基对苯二酚具有较高的1O2淬灭总速率常数（分别为1.42×109 M−1s−1和4.35×108 M−1s−1），并且二者均以物理淬灭为主，物理淬灭占比高达98.66%以上；α-生育酚和叔丁基对苯二酚组合可在淬灭1O2的同时有效清除脂质氧化中产生的自由基，最大程度的抑制PS光氧化的C5反应路径，减少羟基/酮基产物和5,6-环氧产物的形成。本项目的开展为有效抑制脂质中甾醇的氧化提供了理论基础和技术支撑，具有较好的应用前景。