Study On The Changes Of Texture Quality And Mechanisms Of Rice During Storage

Rice is one of China's most important staple foods. The characteristics of rice consumption require that rice should go through a period of storage, whilc in the process of storage; its edible quality will decline remarkably, such as the decrease in adhesive force, the worse of flavor and the weakening of flavor etc. Thus, the study of the reasons why the edible quality of rice decreases after storage seems fairly important.This paper used Texture Analyzer to test the texture quality of stored rice and set up an evaluated method of rice quality, analyzed the change of the sample's texture quality index during the process of storage and to study the change of the main chemical elements such as lipid, protein, and starch, etc. and the indexes change of amylase, lipase, and debranching enzyme, etc during the process of storage. All these study is to analyze and study the relationship between the changes of rice texture quality indexes and physical-chemical indexes in the course of storage and then to reveal the mechanism of rice aging and lay the theoretical foundation for rice storage and the improvement of its quality. The study shows that:1. The analysis of the cooking quality indexes, texture quality indexes and their correlation of 13 kinds of rice samples indicated that the stringiness length of rice was significantly correlated with the starch iodine blue of rice and its swelling volume(r=0.774,0.853); the adhesiveness and the dry matter in rice were significantly correlated(r=0.788); the correlative coefficients of hardness and adhesive force with rice water absorbency were 0.736 and 0.971 respectively, while the recoverable work done and hardness work done etc had no significant correlation with rice cooking quality indexes. Therefore, we can use Texture Analyzer to test the hardness, adhesive force, adhesiveness and stringiness length to evaluate the edible quality of rice.2. Under 38℃heat condition, after the rice being cooked, the ratio change trend of its hardness and hardness/adhesive force increased with the increase of storage time, while the indexes such as adhesive force, adhesiveness, stringiness length and recoverable work done etc decreased with the increase of storage time. Besides, with the increase of storage time, the texture indexes changed remarkably. Under the 4℃storage condition, the texture quality of rice had no significantly changed. So 38℃heat storage accelerated the texture quality of rice decline.3. When stored under the 38℃heat condition, the amylose and insoluble amylose content increased as well as -S-S- content and gelatinition temperature (To,Tp,Tc) while the disulfide bond content, fat, lipase activity, debranching enzyme activity andα- amylase activity decreased. All the results above showed that the rice quality declined in heat condition storage.4. Under the 38°C heat storage condition, the rice texture quality indexes and physical-chemical indexes had fairly good correlation. For example, the insoluble amylose content and the adhesive force and adhesiveness were negatively correlated(r=-0.643,-0.757) while the insoluble amylose content and hardness/adhesive force were positively correlated (r=-0.696). The disulfide bond content and adhesiveness were positively correlated (r=0.686) while disulfide bond content and hardness/adhesive force (r=-0.602) are the reverse. The lipase activity and hardness/adhesive force were negatively correlated (r=-0.695) The debranching enzyme activity and adhesive force,adhesiveness were positively correlated(r=0.762, 0.719) while the debranching enzyme activity and hardness/adhesive force(r=-0.628) were the reverse. Theα- amylase activity and the adhesive force were positively correlated (r=0.537) while theα-amylase activity and hardness/adhesive force(r=-0.562) were the reverse.The gelatinition temperature (To,Tp,Tc) and the adhesive force and adhesiveness were negatively correlated while gelatinition temperature and hardness/adhesive force were the contrary. Such results showed that in the process of storage, the changes of amylose content, insoluble amylase, disulfide bond content, lipase activity, debranching enzyme activity, and amylase activity etc can all influence the change of rice texture quality.