基于玻璃化转变的稻谷爆腰产生机理分析

Fissure formation in rice kernel based on glass transition theory

稻谷爆腰是造成碎米的主要原因之一,为此,人们一直在探讨产生稻谷爆腰的机理。介绍了一种新的稻谷爆腰机理——基于玻璃化转变的稻谷爆腰机理。根据该机理分析了稻谷干燥和缓苏过程中爆腰的产生原因。基于玻璃化转变的稻谷爆腰机理,干燥过程中,当稻谷颗粒由外表向里形成玻璃态时,颗粒内部形成玻璃态和橡胶态两个部分。由于玻璃态和橡胶态的弹性模量和膨胀系数有很大的差别,因此在一定水分梯度条件下,银纹(微裂纹)从两者交界处产生,并可能进一步扩展成爆腰。稻谷缓苏过程中,颗粒内部如果存在橡胶态区,则其不同含水率部分就会在不同水分梯度下分别进入玻璃态,如果此时水分梯度足够,就会引起各部分不均匀收缩和各不相同的应力、应变,这样使玻璃态层产生大量银纹,银纹持续生长即产生爆腰。最后,介绍了两种控制稻谷爆腰的干燥工艺——变温干燥工艺和高温干燥工艺。

The fissure formation in rice kernel has been studied by many researchers, because it is the major cause to reduce the head rice yield. The reason for fissure formation based on glass transition was introduced during drying and tempering in this paper. In the course of drying, the glass state was formed in kernel appearance and inner part of kernel was still in rubbery state, and there was an interface between rubbery and glass state. Because the thermal expansion coefficient of rubbery state was many times larger than that of glass state, the tiny fissure formed in the interface between rubbery and glass state under an enough moisture gradient, and then the tiny fissure extended to a big fissure. In the course of tempering, the different parts of rubbery state in kernel can transit to glass state under different moisture gradients, the tiny fissure formed in the part of glass state. Based on the above analysis, two methods to prevent the fissure formation can be obtained. One method is changing temperature drying, the rice kernel must still be in glass state during drying. The other method is high temperature drying, the rice kernel must still be in rubbery state.