| Rice is one of the most widely cultivated cereals in the world and a staple food consumed by nearly half of the world's population,especially in Asia,South America and Africa.Although a small amount of rice crops are used as food ingredients and feed ingredients.However,most of them are used as rice for cooked consumption,and this pattern of usage leads to the need for rice storage in different periods.During storage,many changes have taken place in the physical and chemical properties of rice,commonly known as rice aging.The rice aging usually leads to a worse quality,which seriously affects its economic benefits.Therefore,studying the aging mechanism of rice to solve the problem of rice quality plays an important role in improving the economic value of rice.This study focuses on starch to explain the trend and role of starch fine structures and physiochemical properties in the aging process of rice.The main research results are as follows:1.The results showed that the grain color changed during the storage of brown rice under the environment of high temperature and high humidity,through the measurement of the appearance of rice grains and the morphological structure of starch granules of 11 rice samples,and the grain surface gradually became darker and darker,showing a dark brown color.After storage,the hardness of the polished rice grains decreased and became brittle and broken.2.The preliminary physical and chemical quality measurement results showed that the protein content and total starch content of 11 rice samples were not affected by storage environment and period,but the apparent amylose content of rice variety LP93,Yongyou 2640,Nangeng 2728,Nangeng 42 significantly reduced,which indicated that the aging environment and period had different effects on different rice samples.The taste quality of the rice was measured by a taste meter.The results showed that the aroma,integrity,taste and mouthfeel of these samples all decreased to varying degrees,and the comprehensive taste value also decreased.3.The fine structure of starch was determined by FACE and SEC.The results showed that the medium and long chains of amylopectin in starch were significantly reduced during the rice storag,and the medium and long chains of amylopectin were degraded to shorter branches.The content of amylose was significantly reduced,the short and medium chains of amount and chain length of amylose were significantly reduced,and the molecular size of starch was significantly reduced.In addition,XRD results showed that aging did not change the crystalline type,but will significantly reduce the crystallinity degree.The microstructure of starch granules observed did not change significantly using SEM.4.The main physical and chemical qualities of 11 kinds of rice samples were determined.DSC results showed that the value of onset temperature(To),peak temperature(Tp)and conclusion temperature(Tc)of rice during storage were significantly reduced,indicating the gelatinization temperature was significantly reduced.Besides,the enthalpy value was significantly reduced.The RVA results showed that the peak viscosity,trough viscosity,breakdown value,final viscosity and set back value increase significantly.5.According to the established structure-property relationship in this study,the structural change is related to the observed lower aging temperature and enthalpy,higher peak viscosity and final viscosity after aging.The changes of amylose and amylopectin on starch will affect the physical and chemical properties of starch and rice.At the same time,this effect depends on different rice variety. |
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