Study On Molecular Structure And Physicochemical Characteristics Of Glutinous Rice Starch

Molecular structure, physicochemical properties and their relationship of glutinous rice starch from different varieties and areas in Hubei Province were studied, Result indicated:1. Molecular structure of glutinous starchGlutinous rice starch mainly consists of amylopectin and intermediate fraction, accounting for 25.29%-63.42% and 27.93%-55.56%, respectively. Molecular weight of glutinous rice amylopectin was range in 8.96×107g/mol～7.96×109g/mol. Varieties and areas have no significant influence on starch fraction content and its molecular weight.The suitable conditions for separation of glutinous rice amylopectin by gradient centrifugation as follows:1% starch suspension heated for 8min after pasting, then centrifuged by 9000r/min for 30min at 4℃, the supernatant was centrifuged by 12000 r/min for 30min at 4℃, and the precipitation was amylopectin. The purity of amylopectin isolated by gradient centrifugation was high, and the isolated amylopectin was pherical structures in aqueous solution.2. Physicochemical properties of glutinous starchGranularity of glutinous rice starch, whose dimensional appearance was polyhedron or globe, was 2μm-10μm. Blue value, crystallinity, intrinsic viscosity, paste properties and creep properties differed from different rice varieties, areas and harvest time. The pasting temperature of glutinous rice starch sol was lower than that of glutinous rice starch gel.Glutinous rice starch gel shows high diaphaneity, good viscoelastic and stability for storage. With the storage time extension, the relaxation time, viscosity coefficient of starch gel reduced during storage, while retard elastic modulus increased, indicating the hardness of starch gel increased and viscoelastic reduced. The variation trends of retard elastic modulus, relaxation time and viscosity coefficient during storage couled be describled by Exponential mathematical models, and their variation rate were correlated with fraction contents, molecular weight of glutinous rice amylopectin, crystallinity and storage temperature.Areas of starch had influence on residual protein contents, BV, intrinsic viscosity of glutinous rice starch and the retard elastic modulus, relaxation time and viscosity coefficient of starch gel. The residual protein contents of glutinous rice starch from Hanchuan were high, while its intrinsic viscosity was low. The relaxation time of starch gel from Yingcheng, Hanchuan and Jingshan was high.Varieties of starch had influence on residual protein contents, BV, intrinsic viscosity of glutinous rice starch and the retard elastic modulus, relaxation time and viscosity coefficient of starch gel. The residual protein contents and BV of Zajiao glutinous rice starch was high, while its intrinsic viscosity was low. Intrinsic viscosity and BV of Zhenzhu and Jingnuo glutinous rice starch was high. The relaxation time of Jingnuo and Zajiao glutinous rice starch gel was low, indicating the hardness of starch gel was low and viscoelastic was high.3. Correlation analysis between molecular structure and physicochemical propertiesStarch molecular structure had influence on its physicochemical properties. The higher starch fraction content was, the faster ageing rate of starch gel was. The lower molecular weight of amylopectin or crystallinity was, the faster ageing rate of starch gel was. The higher amylopectin molecular weight or crystallinity or amylopectin content was, the higher relaxation time of its starch gel and the lower viscosity coefficient was, indicating that starch gel for good stability for storage...