Extraction of protein from distiller’s grain

We have investigated the feasibility of extracting the oil and protein from distiller’s grain (DG) to obtain a higher-valued protein-rich product and a carbohydrate-rich residue better suited for conversion to fermentable sugars. Protein extractions based on aqueous ethanol, alkaline-ethanol, and aqueous enzyme treatments were compared. Three of the methods extracted a significant amount of the protein from dried, defatted DG (DDDG). The enzymatic extraction decreased the crude protein content in the solid phase for both milled and unmilled DDDG from 41% (dry weight) to approximately 10% (dry weight) protein in the residual solid; this corresponded to extraction of 90% of the protein in the original DDDG. The alkaline-ethanol extraction was similarly effective for milled but not unmilled DG. Simple extraction with alcohol was not as effective. Amino acid analysis of each protein extract was consistent with it consisting mainly of zeins. For the protease-assisted extractions, 95% the proteins were in the form of peptides smaller than 10 kDa.