稻米爆腰机理与碎米率

The Mechanism of Brown Rice Kernel Cracking Rate and Rice Broken Rate

碾米过程中产生的碎米率与稻谷中的糙米的爆腰率有重要相关关系。米粒的主要成分是淀粉,淀粉以一定的晶体结构排列在米粒的胚乳细胞壁中,当淀粉在受热和受潮时,淀粉粒膨胀,使米粒产生热应力和水分应力差,当此拉应力大于米粒抗拉强度时,米粒内部就产生裂纹而形成爆腰米粒。稻谷在收获后期、收获后的干燥、贮藏中均会受到温度和水分变动而产生爆腰米粒,稻谷在加工过程中受到机械力的作用也会增加米粒的破碎。所以,降低碎米率应该从稻谷的收获后期就引起注意,防止温度和水分过大的波动,在稻谷加工中米粒应避免拉伸和弯曲的作用。

China is a major country of producing rice in the world. It can produce great social and economic benefits to decrease rice broken rate. This paper and some former researches indicate that the rice broken rate in the rice milling process has great relationship with the brown rice kernel cracking rate. So to reduce the rice broken rate, it is essential to decrease rice kernel cracking rate. Brown rice contains 75%±starch. The starch grain arranges in the cell wall of endosperm according to some kinds of crystal structure, between them is protein which affects rice strength and its quantity is different according to rice varieties. The rice tensile strength is between 9. 8×10~5-9. 8×10~6 Pa. The starch can expand when it absorbs moisture or being heated, and the humid coefficient of expansion is greater than that of temperature. So the rice grain can produce inner stress difference when it absorbs moisture or being heated, when the inner stress is greater than the tensile strength, rice kernel will crack, and they will break during hulling and milling process. In order to reduce rice broken rate, humidity and temperature should keep constant during the rice late ripening stage, drying and storage period, it should not be affected by tensile or bending strength during process period.