Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2008
Publication Date: 11/1/2008
Citation: Zhao, R., Bean, S., Wang, D. 2008. Sorghum Protein Extraction by Sonication and Its Relationship to Ethanol Fermentation. Cereal Chem. 85:837-842.
Interpretive Summary: Sorghum proteins form web-like cross-links during the fermentation process. These cross-links tie up starch and reduce its availability for fermentation. Thus, protein cross-linking is a measure of fermentation quality in sorghum. In order to predict the fermentation efficiency of sorghum, a rapid method to extract polymeric proteins from sorghum using ultrasound was employed. The amount of extractable protein in sorghum was correlated to the ethanol efficiency. Thus, area of proteins from mashed sorghum using sonication could be used as an indicator for predicting fermentation quality of sorghum.
Technical Abstract: The objectives of this research were to develop a rapid method for extracting proteins from mashed and non-mashed sorghum meal using sonication (ultrasound), and to determine the relationships between the levels of extractable proteins and ethanol fermentation. Nine grain sorghum samples with a broad range of ethanol fermentation efficiencies were used. Proteins were extracted in an alkaline borate buffer using sonication and characterized and quantified by SE-HPLC. A 30-sec sonication treatment was found to extract a lower level of proteins from non-mashed sorghum meal than by extracting the proteins for 24 h with buffer only (no sonication). However, for the mashed samples, sonication extracted more protein than did the buffer only 24 h extraction. In addition, sonication extracted more polymeric proteins from both the mashed and non-mashed samples compared with the buffer only extraction method. CFLSM images showed that the web-like protein microstructures were disrupted during sonication. The results showed that there was a strong relationship between extractable proteins and fermentation efficiency. Ethanol yield increased and conversion efficiency improved significantly as the amount of extractable proteins increased. Absolute amount of polymeric proteins from sonication extract were also highly related to ethanol fermentation. SE-HPLC area of proteins from mashed sorghum using sonication could be used as an indicator for predicting fermentation quality of sorghum.