稻米的品质和影响因素

稻米品质应从碾米、外观、蒸煮、食味、营养等方面来衡量，有时还要考虑安全、贮藏、加工和卫生等性质。淀粉和蛋白质的种类与数量决定了稻米的品质。一般来说，直链淀粉含量在20％以上的稻米品种食味差；直链淀粉含量在15％——20％以下的食味较好；蛋白含量超过9％的品种其食味往往较差。稻米中垩白出现部位与灌浆物质的输入途径有关。离背部维管束远的腹部胚乳细胞易充实不良形成垩白。稻米品质形成是品种遗传特性和环境条件综合作用的结果。环境条件对稻米品质的影响是通过影响稻株和颖果的生理过程而发挥作用的。过多施用氮素，特别是灌浆期间氮素过多，会使米中的蛋白质含量显著提高，垩白率降低，然而食味变差。饭的食味还与煮饭方法、煮饭后食用时间有关。通常将米用水先浸1—2小时后煮，饭在煮好后的半小时时食用，食味最佳。

Rice Quality and its Affecting Factors

Rice quality usually includes the quality of milling, appearance, cooking, taste and nutrition, and the quality of safety, storage, processing and health is also involved. The type and amount of starch and protein have a great effect on the rice quality. Generally, the rice with 15%-20% amylose always has a fine taste, while the rice with more than 20% amylose or 9% protein is distasteful. The region of chalk is associated with the way of filling substance importing into the endosperm, that is, the abdominal endosperm cells far from the dorsal vascular bundle are easily to form chalk. On the other hand, rice quality is resulted from the interaction between the inheritance of variety and environmental conditions, which affects rice quality by their physiological influencing on rice plant and caryopsis. When the nitrogenous fertilizer is applied overmuch, especially during the filling period, the protein content of rice will be remarkably increased, and the chalky areas be reduced, while the rice tastes poorly. The taste of rice is also influenced by ways of cooking and eating time after cooking. The rice will have the best taste when it is dipped into the water for one or two hours before cooking, and is tasted delicious about thirty minutes after being cooked.