大米淀粉的分子量分布及其与粘性的相关性研究

Molecular Weight Distribution of Rice Starches and Its Correlation with Viscosity

目的研究大米淀粉的分子量分布和粘性,探讨天然淀粉(直链淀粉和支链淀粉的混合体系)的分子结构与特征粘度的关系。方法以6种大米淀粉为原料,采用凝胶色谱法和乌式粘度计测定大米淀粉的分子量分布和特征粘度,用非线性回归拟合分子量分布与特征粘度关系的数学模型。结果大米淀粉主要由支链淀粉、中间级分和直链淀粉3个级分组成。6种大米支链淀粉的平均相对分子质量约为0.90×108～15.60×108 g.mol-1,直链淀粉的平均相对分子质量约为4.06×106～6.58×106 g.mol-1。支链淀粉分子的分子量分布范围较直链淀粉分子的窄。中间级分的分子量分布较宽。大米淀粉的特征粘度约为77.65～237.53 g.g-1。结论天然大米淀粉的比浓粘度、比浓对数粘度与浓度的关系呈二次曲线的特征。当支链淀粉的平均相对分子质量和摩尔比较大时,淀粉的特征粘度较高,较大的直链淀粉平均相对分子质量和摩尔比使特征粘度减小,用指数模型拟合淀粉分子量分布规律与特征粘度的关系可以达到较高的精度,该模型可为定量描述天然淀粉或直链淀粉和支链淀粉混合体系的粘度与其分子结构的关系提供一种方法。

[Objective] The relationship between molecular weight distribution and intrinsic viscosity of rice starches （amylose-amylopectin mixed system）was studied. [ Method ] The molecular weight distribution rule and intrinsic viscosity on rice starches were measured by gel permeation chromatography and Ostwald viscometer, respectively. Numerical model of their relationship was fitted by non-linear regression. [Result] Rice starch has 3 main fractions, amylose, intermediate and amylopectin. Relative molecular weight of rice amylopectins is about 0.90× 10^8 - 15.60× 10^g·mol^-1, while that of rice amyloses is about 4.06× 10^6 -6.85× 10^6 g·mol^-1. The molecular weight distribution of rice amylopectin is narrower than rice amylose. The molecular weight distribution of intermediate is wider. The intrinsic viscosity of rice starches is about 77.65 - 237.53 g·g^-1. [Conclusion] ηsp/c and lnηr/c of native rice starch assumed quadratic curved lines relations with c. When molecular weight and molar ratio of amylopectin are bigger, intrinsic viscosity is higher. But amylose with bigger molecular weight and higher molar ratio may make intrinsic viscosity to be lower. An exponential model could describe the relationship between molecular weight distribution and intrinsic viscosities of rice starches accurately. The model provides a way to determine the relationship between the intrinsic viscosities and molecular structures of natural rice starches amylose- amylopectin mixed system quantitatively.