Study On The Control Mechanism Of Starch Regeneration During Rice Steaming In Early Indica Rice

Early indica rice is an important variety of Grain Reserve in China,but its edible quality is poor,and it is rarely used for food.As a kind of rice stored in the warehouse of grain purchasing enterprises,it can effectively solve the problem of low utilization rate of early indica rice resources,which is conducive to stabilizing the production of early indica rice and improving the level of national food security.During the soaking and cooking process of steamed rice,water,starch,protein and fat in rice will change and distribute unevenly,and the gelatinization degree of starch granule is also different.Therefore,the mechanism of starch retrogradation in this heterogeneous starch paste system is more complex.The research on starch retrogradation and its control mechanism in the processing of steamed rice will help to deepen the understanding of starch retrogradation mechanism in heterogeneous starch paste system,improve the quality of steamed rice,and promote the futher development of steamed rice industry in China.Around the above problems,this project carried out three parts of research content:(1)the preparation of early indica rice starch and its physical and chemical properties;(2)the effect of the processing process of early indica rice steamed rice on starch retrogradation;(3)the physical and chemical properties of different flour layers of steamed rice.The following conclusions can be drawn from the research:(1)Amylose,amylopectin and resistant starch accounted for 22.31%,75.46%and 1.81%,respectively.The crystal characteristics of early indica rice starch were measured by X-ray diffraction.The amorphous substance and crystal form of early indica rice starch were identified,and the early indica rice starch was a type.There was a V-shaped crystal absorption peak at 21 ° which indicated that amylose lipid complex appeared in early indica rice starch.The fitting relative crystallization rate of early indica rice starch was 35.2%,which was higher than that of corn starch and potato starch,and its aging degree was lower,and the content of resistant starch was lower.The thermal properties of early indica rice starch were detected by DSC.There was a large endothermic peak of early indica rice starch at 56.6?,indicating that the crystal disintegrated at this temperature,and a small endothermic peak appeared at 92?,indicating that the amylose lipid complex crystal of early indica rice starch disintegrated.The vibration absorption peak intensity of each functional group of starch was obtained by FT-IR.The peak value of 1047/1020 cm-1 was compared.The crystallinity of early indica rice starch was 0.72,that of potato starch was 0.74,and that of corn starch was 0.7 1.The aging degree of early indica rice starch and jade rice starch was lower than that of potato starch,and early indica rice starch was easy to age.(2)The effect of soaking,cooking and drying on starch retrogradation in the process of steaming rice was studied.The enzymolysis power was used as the measuring index.The higher the enzymolysis force was,the smaller the retrogradation degree of starch was.In the soaking process,the enzymolysis power first increased and then decreased in the range of pH 4.0-9.0,and reached the maximum value at pH 6.0;in the range of 2.0-6.0 h,the enzymolysis power increased with the increase of soaking time;in the range of 45-60?,the enzymolysis power increased with the increase of soaking temperature,and had little change at 60-70?.The results showed that the gelatinization degree of rice reached the best when soaking at pH 6.0 and 70? for 4.5 h.the lower the retrogradation of starch in steamed rice,the lower the content of resistant starch and easier to digest.In the cooking process,the enzymatic hydrolysis power increased with the increase of cooking time and cooking temperature in the range of 5-30 min and 75-100?.The amylase hydrolytic power of steamed rice reached the maximum when the cooking temperature was 100? and the cooking time was 30 min.at this time,the starch gelatinization degree was the highest,the aging degree was low,and the content of resistant starch was low.In the drying process,in the drying time range of 1.0-3.5 h and the drying temperature of 50-100?.the enzymatic hydrolysis ability increased with the increase of drying time and drying temperature.The main reason is that after soaking and cooking,the starch completely gelatinizes,the aging degree of starch decreases rapidly,and the content of resistant starch decreases.(3)Compared with early indica rice,the physicochemical properties of inner and outer layers of steamed rice were studied.The results showed that:the amylose and amylopectin of each layer of rice flour of steamed rice were earlier than those of indica rice,and the amylopectin decreased faster.The content of resistant starch in each layer of steamed rice was earlier than that of indica rice,indicating that the processing of steamed rice had a great influence on starch retrogradation.There is an obvious absorption peak at 19 ° in the inner layer and whole rice flour of steamed rice,which is the characteristic peak of straight chain fat complex and forms V-shaped crystal.At 20°there are steamed rice and early indica rice,and the outer layer of rice flour has a multiple diffraction peak,which may be a V-type crystal of fiber.The relative crystallinity of rice flour and starch in each layer of steamed rice was earlier than that in indica rice.Compared with early indica rice,steamed rice showed lower phase transition temperature and gelatinization enthalpy,and steamed rice starch showed higher phase transition temperature and gelatinization enthalpy,but the gelatinization temperature range of steamed rice flour and starch was narrow,so it was difficult to aging.From the rice flour and starch of each layer of steamed rice,we can know the change of starch retrogradation degree of steamed rice,which indicates that non starch substances have great influence on starch retrogradation.