米谷蛋白氧化对稻米蒸煮食用品质影响及机理研究

A series of interrelated changes of starch, lipid, and protein of rice occurred during ageing, and oxidative modification of oryzenin structure contributed to the decline of cooking and eating quality of rice during storage. For the mechanism of effects of ageing on cooking and eating quality of rice is not entirely clear, and effects of the measure which used to delay ageing of rice were not perfect. Therefore, mechanism of effects of ageing on cooking and eating quality of rice was investigated from the point of view of oryzenin oxidation in the present work. Simple oxidation system of oryzenin and three kinds of lipid oxidation products was used to simulate oxidative stress environment of oryzenin during storage. Mechanism of oryzenin oxidation and effects of oxidative modification on the structure of oryzenin were studied. Properties of urea-induced unfolding and aggregation of oxidized oryzenin, thermally induced denaturation and aggregation of oxidized oryzenin, and oryzenin-starch interaction of aged rice were also characterized. Results of the above-mentioned were associated with micro-structure as well as cooking and eating quality of rice, which could further understand the mechanism of rice ageing and mechanism of effects of ageing on cooking and eating quality of rice, and provide a theoretical basis for the quality control of rice during storage.

稻谷在陈化过程中淀粉、脂质和蛋白质发生系列变化，其中米谷蛋白结构氧化性修饰是导致稻谷储藏过程中稻米蒸煮食用品质下降的重要原因。针对目前对于陈化影响稻米蒸煮食用品质的机理还不甚明晰和延缓稻谷陈化措施的效果还不甚理想的现状，本项目从米谷蛋白氧化的角度研究陈化影响稻米蒸煮食用品质的机理。通过构建米谷蛋白与三种脂质氧化产物的单纯氧化体系模拟稻谷储藏过程中米谷蛋白的真实氧化应激环境。通过考察米谷蛋白的氧化机理以及氧化修饰对米谷蛋白结构的影响，研究氧化米谷蛋白尿素去折叠性质、尿素去折叠后聚集性质、热变性和热聚集性质，表征陈化稻米中米谷蛋白-淀粉相互作用的性质，并将它们与陈化稻米的蒸煮食用品质和微结构相关联，从而进一步认识稻谷陈化机理和陈化影响稻米蒸煮食用品质的机理，为稻谷在储藏过程中的品质控制提供理论依据。

大米蛋白结构氧化性修饰是导致稻谷储藏过程中稻米蒸煮食用品质下降的重要原因。针对目前对于陈化影响稻米蒸煮食用品质的机理还不甚明晰的现状，本项目从大米蛋白氧化的角度研究陈化影响稻米蒸煮食用品质的机理。首先以新收获籼米和粳米品种为原料，采用人工加速陈化条件研究贮藏对大米蛋白氧化程度、结构特性和功能性质的影响，证明了稻米在贮藏过程中大米蛋白逐渐氧化，结构特征和功能性质也随之改变；接着采用2,2'-偶氮二(2-脒基丙烷)二盐酸（AAPH）热分解产生的过氧自由基、HPODE （脂质氢过氧化物）、丙二醛（MDA）分别代表脂质过氧化反应过程中产生的脂质自由基、脂质氢过氧化物和活性醛，研究三种氧化体系对大米蛋白氧化程度、结构特征和功能特性影响，确定了过氧自由基和MDA共同参与稻米贮藏过程中大米蛋白的氧化修饰，并以MDA氧化修饰为主；氧化大米蛋白易于发生去折叠反应，而不易发生复折叠反应，蛋白质氧化导致大米蛋白结构稳定性下降；蛋白质氧化导致大米蛋白热稳定性下降。在大米蛋白热变性过程中，大米蛋白粒径随温度的升高而逐渐增大，热变性过氧自由基氧化大米蛋白的粒径随着蛋白质氧化程度的上升而下降，而同等热变性条件下丙二醛氧化大米蛋白的粒径则随着丙二醛添加浓度的增加呈现先上升后下降趋势，热变性大米蛋白冷却后的粒径和热聚集体含量均随着蛋白质氧化程度的增加而减少；陈化导致大米蛋白形成二硫键以及疏水相互作用，通过抑制大米淀粉颗粒的糊化性质降低稻米的蒸煮食用品质。以新收获籼米、粳米和糯米为原料，采用人工加速陈化实验比较贮藏过程中三种稻米的蒸煮特性和耐贮性，结果发现糯米的耐贮性最差，籼米耐贮性最好，粳米居中。这些研究结果可进一步认识稻谷陈化机理和陈化影响稻米蒸煮食用品质的机理，为稻谷在储藏过程中的品质控制提供理论依据。