Determination Methods For Sorghum Starch And Its Physicochemical Properties

Chinese sorghum liquor has a long history and is renowned the world. Starch is themain ingredient of sorghum which is composed of two types of macromolecules,including the linear amylose and the highly branched amylopectin, and its content hasan essential effect on the liquor yield and brewing quality. However, methods fordetermining the content of two types of starch simultaneously in sorghum now aresingle and complex. Here, a novel method was proposed to address that question.Compared with the existing methods, this way was easier and more precise. In addition,the physicochemical properties of different sources of sorghum starches were studied.Research of this article included the following parts:①Isolation of amylose and amylopectin in sorghum starch. The distinctive UVabsorption spectra of different starches would bring error when measuring its content.So the sorghum amylose, amylopectin were separated by N-butanol method and theirpurity were confirmed by UV spectroscopy, blue values and gel filtrationchromatography. The results showed that the separated amylose, amylopectin insorghum conformed to the requirements of the experiment. The λmaxof theiodin-amylopectin compound and iodin-amylose compound located at540nm and640nm, respectively.②A new method for determination of starch content in sorghum was established byusing UV-visible absorption spectroscopy. Measuring the absorbance values ofcompound of amylose, amylopectin and the mixture of both with iodine in the400-800nm suggested that each component had an additive effect on the final ultravioletabsorption and would not interfere with each other. Therefore, the absorption values oftwo substances at the specific wavelength could be separated from mixed absorptionvalue using a mathematical method, then calculated the content based on the method ofone-component calculations. This method could determine amylose, amylopectincontent simultaneously and it was simple, convenient. The results of recovery rate testwere between95%~105%showed that the method had high accuracy. Seven sorghumstarches content were measured using this method, found-ing that Southern sorghumcontained low amylose, like GuoJiao、Lu Nuo had no amylose, but the amylose contentof Northern sorghum more than13%.③The physicochemical properties including granules, crystallinity, pasting properties of starches from different brewing sorghum were studied by means ofScanning electron microscopy(SEM), X-ray diffraction (XRD), and rotational rheometer.The results were as follows: Compared with the North sorghum starch, Southernsorghum granule corners were more rounded and had more honeycomb, the diameter ofgranules were smaller; X-diffraction spectrum showed that the crystal structure ofsorghum starch exhibited A type. The relative crystallinity of Southern sorghum weremore than30%, while the North sorghum were20~25%; The gelatinization temperatureand the peak viscosity of Southern sorghum starch were relatively higher, theregenerative value were smaller compared to the North sorghum starch; The enzymehydrolysability of Southern sorghum were greater than that of North sorghum.