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The impacts of protein on grain sorghum ethanol fermentation efficiency

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2007 ASAE Annual Meeting  076158.(doi:10.13031/2013.23339)
Authors:   Renyong Zhao, Scott R Bean, Donghai Wang
Keywords:   Sorghum, ethanol, fermentation, protein, digestibility, mashing, FAN, HPLC

Nine grain sorghum samples with a broad range of ethanol fermentation efficiencies (EFE) were used for this study. Relationships between free amino nitrogen (FAN), protein digestibility, protein extractability, and protein microstructure to EFE were investigated. Only 0.60%~1.20% of sorghum protein was liberated in the form of free amino acids during mashing and this amount of FAN was not enough to support yeast fermentation. Protein digestibility reduced significantly during mashing. No strong linear relationship between protein digestibility and EFE was observed after mashing. However, there was a strong linear relationship between EFE and the amount of extractable protein from mashes. The extractable protein could be used for prediction of EFE. The proteins extracted with sonication induced by 2% ß-mercaptoethanol and separated by SEC showed that the extractable non-disulphide cross-linked oligomers were positively related to EFE. Confocal laser scanning was used to analyze the effect of mashing on protein structure. The images showed that sorghum proteins tended to form highly extended, strong web-like microstructures during mashing. The degree of protein cross-linking was different among samples. The formation of web-like microstructures due to cross-linking reduced EFE.

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