|Zhao, Renyong - KANSAS STATE UNIVERSITY|
|Wang, Donghai - KANSAS STATE UNIVERSITY|
|Boyle, Daniel - KANSAS STATE UNIVERSITY|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 10, 2007
Publication Date: January 16, 2008
Citation: Zhao, R., Bean, S., Ioerger, B.P., Wang, D., Boyle, D.L. 2008. Impact of Mashing on Sorghum Proteins and Its Relationship to Ethanol Fermentation. Journal of Agricultural and Food Chemistry. 56:946:953. Interpretive Summary: Sorghum proteins are known to cross-link strongly when wet cooked, such as occurs during ethanol production. This cross-linking may influence ethanol yields and fermentation time by reducing access by enzymes to the starch. Thus the objectives of this research were to investigate the changes that occur to sorghum proteins during mashing and how this impacts the fermentation process. Protein solubility experiments and analysis of proteins by chromatography showed that sorghum proteins formed highly cross-linked weblike structures during mashing. The degree of protein cross-linking was different among varieties. More fluffy microstructures were observed in varieties with higher conversion efficiencies. Web-like protein matrix held not only starch granules but also some oligosaccharides or polysaccharides inside. The formation of web-like microstructures due to cross-linking reduced conversion efficiency.
Technical Abstract: Nine grain sorghum varieties with a broad range of ethanol fermentation efficiencies were selected to characterize the changes in sorghum protein in digestibility, solubility and microstructure during mashing and to relate those changes to ethanol fermentation quality of sorghum. Mashing reduced in vitro protein digestibility considerably. As a marker of cross-linking, protein digestibility of original samples was highly related to conversion efficiency. Gamma-kafirin (%) neither correlated to ethanol yield nor conversion efficiency significantly. Solubility of proteins in an alkaline borate buffer in junction with SDS decreased substantially after mashing. A large amount of polymers cross-linked by disulfide bonds developed during mashing. There might be non-disulphide cross-links existing in sorghum proteins after mashing. Solubility and SE-HPLC area of proteins extracted from mashed samples were highly correlated with ethanol fermentation. Ethanol yield increased and conversion efficiency improved notably with the increase of extracted proteins from mashed samples. SE-HPLC total area could be used as an indicator to predict ethanol fermentation. CFLSM images proved that sorghum proteins tended to form highly extended, strong web-like microstructures during mashing. The degree of protein cross-linking was different among varieties. More fluffy microstructures were observed in varieties with higher conversion efficiencies. Web-like protein matrix held not only starch granules but also some oligosaccharides or polysaccharides inside. The formation of web-like microstructures due to cross-linking reduced conversion efficiency.