ENHANCED END USE QUALITY AND UTILIZATION OF SORGHUM GRAIN
Location: Grain Quality and Structure Research Unit
Title: Characterization of polymeric proteins from vitreous and floury sorghum endosperm
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 14, 2007
Publication Date: December 1, 2007
Citation: Ioerger, B.P., Bean, S., Tuinstra, M.R., Pedersen, J.F., Erpelding, J.E., Lee, K.M., Herrman, T.J. 2007. Characterization of polymeric proteins from vitreous and floury sorghum endosperm. Journal of Agricultural and Food Chemistry. 55:10232-10239.
Interpretive Summary: Grain hardness is an important end-use quality trait in sorghum. Grain hardness is important not only in milling and food quality, but also in insect and weathering resistance. The exact mechanism controlling grain hardness in sorghum is not yet fully understood. This project examined the differences in protein cross-linking between different parts of the sorghum grain which has been thought to play an important role in sorghum grain hardness. We found that proteins extracted from hard endosperm appeared to be more cross-linked than proteins extracted from floury (soft) endosperm. Through understanding the factors controlling grain hardness in sorghum it may be possible to manipulate these factors to produce sorghum with improved quality traits, benefiting sorghum producers, the grain industry, the cereal food industry, and the animal feed industry.
Differences in protein content and composition between vitreous and floury endosperm were investigated using a number of different techniques. Differences in protein cross-linking between vitreous and floury endosperm was investigated using differential solubility, size exclusion chromatography (SEC), and analysis of sulfhydryl content and composition. Vitreous endosperm was found to have higher levels of total protein and kafirins, but floury endosperm had a higher proportion of ' kafirins than the vitreous. Floury endosperm was found to have higher levels of SDS soluble proteins than SDS insoluble proteins extracted using sonication than vitreous endosperm. Conversely, vitreous endosperm had a greater proportion of the insoluble proteins than the soluble. SEC analysis of the polymeric proteins revealed that the insoluble proteins had more polymeric proteins than did the soluble proteins, indicating greater cross-linking and a larger Mw distribution. Vitreous endosperm was also found to have a greater percentage of disulfide bonds than floury endosperm. These results show that the proteins in vitreous endosperm have a higher degree of cross-linking and a greater Mw distribution than those found in floury endosperm.