STUDIES ON THE ELUCIDATION OF THE PHYSICOCHEMICAL BASIS OF SORGHUM GRAIN QUALITY
Abstract
Fifteen sorghum cultivars differing widely in grain hardness (percent vitreousness) were studied to determine the relationship of grain hardness on some physical and chemical parameters for differentiating texture of cooked sorghum. For further elucidation of the influence of starch on the texture of cooked sorghum, this chemical component was isolated from the floury and corneous endosperm fractions of some sorghum cultivars, and characterized. Adhesion test, cooked grain texture test, and alkali gel stiffness test are equally reliable physical indices for predicting texture of cooked sorghum. These tests were observed to be strongly influenced by the percent vitreousness of the sorghum cultivar. Other tests such as alkali digestibility, and amylography are less useful measures of cooked sorghum texture. BEPT seemed not to influence the texture of cooked sorghum and grain hardness. Soluble and kafirin proteins, total and hot-water soluble amylose were the major chemical components identified to be related to cooked grain texture. The level of these chemical constituents in the endosperm appeared to be significantly influenced by the percent vitreousness of the grain. The floury and corneous endosperm fractions isolated from the same sorghum cultivar exhibited different levels of protein content and alkali gel stiffness value. The CP/MAS-('13)C-NMR spectral pattern of these endosperm fractions exhibited distinct differences in the starch and protein regions. The starch isolated from the floury endosperm fraction exhibited lower intrinsic viscosity, faster rate of lintnerization, larger mass median diameter, higher iodine binding capacity and higher amount of amylose than the starch from the corneous endosperm fraction. It can be concluded that the starch and polymeric components of the floury endosperm fraction have lower molecular weight and size, and are less crystalline in structure compared to the ones from the corneous endosperm fraction. Consequently, the softer alkali gel exhibited by the floury endosperm fraction is accounted for by the above starch properties. This was supported by the strong relationship between alkali gel stiffness value of sorghum endosperm and intrinsic viscosity.
Degree
Ph.D.
Subject Area
Agronomy|Food science
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