Protein-Rich Residue from Wheat Alcohol Distillation: Fractionation and Characterization

Cereal Chern. 61(5): 423-427 Whole wheat and flour were fermented to make alcohol. The residue, after alcohol was distilled, was fractionated into distillers' grains, centrifuged solids, and distillers' solubles. Distillers' grains and centrifuged solids had protein contents of 29 and 57%, respectively, and accounted for Fermentation of cereal grains to make alcohol produces a protein-rich material (stillage) after the alcohol is distilled. The fermentation process predominantly consumes the starch in cereal grains, and other nutrients such as protein are thereby concentrated. Alcohol fermentation of corn is done commercially, and a small amount of wheat is also used for this purpose. Fractionation and characterization of corn stillage and of corn distillers' dried grains with and without solubles were reported previously (Wu et al 1981, Wu and Stringfellow 1982). Satterlee et al (1976) prepared protein concentrate from fermented corn and fermented wheat by extraction with alkali. Tsen et al (1982, 1983) incorporated distillers' dried grain flours in bread and cookies. Prentice (1978) and Prentice et al (1978) blended brewers' spent grain with flour for muffin and cookie formulations. Finley and Hanamoto (1980) incorporated various fractions of brewers' spent grains into bread. Some composition data on wheat distillers' grains and wheat distillers' grains with solubles are available l tv1ention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over others firms or similar products not mentioned. This article is in the pUblic domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Association of Cereal Chemists, Inc., 1984. 36 and 21 % of total hard wheat nitrogen. Half of the nitrogen in distillers' solubles of flour passed through a 10,000 molecular weight membrane. Lysine, expressed in grams per 16 g of N, was considerably higher in distillers' grains and centrifuged solids than wheat. (National Research Council 1956). Since corn is not available for alcohol fermentation in some parts of the United States and various regions of the world, wheat is often used as the substrate for yeast. Wheat and wheat flour differ appreciably from corn and degermed corn flour, respectively, in composition and properties, and the by-products of wheat fermentation may have better characteristics for food than does corn. The purpose of this study was to fractionate and characterize the protein-rich distillation residues from fermented hard and soft whole wheats and their flours. MATERIALS AND METHODS Wheat Newton wheat, a typical hard red winter wheat in Kansas, was grown in 1981. Daws wheat, a soft white winter wheat, was from Washington. The wheat was milled in a laboratory model Allis rolls until all passed through No. 12 screen (whole grain), milled in the Allis rolls until 83% of the wheat passed through No. 12 screen (83% extraction flour), or in a Buhler mill with 70% of the wheat collected in the flour bins (70% extraction flour). Fermentation Ground wheat or wheat flour was dispersed in 5 L of tap water in a 20-L stainless steel, temperature-controlled, jacketed fermentor equipped with stirrers. The dry basis weights used were 2,350, VoI.61,No.5,1984 423 2,065,1,838,1,950, 1,927, and I,81lgforNewtonwheat,Newton flour (83% extraction), Newton flour (70% extraction), Daws wheat, Daws flour (85% extraction), and Daws flour (70% extraction), respectively, The pH of each slurry was adjusted to 6.2, and 6 ml of Miles Taka-therm a-amylase (170,000 Modified Wohlgemuth Units/g) was added. One Modified Wohlgemuth Unit is that amount of enzyme which will dextrinize one milligram of soluble starch to a dextrin of a definite size in 30 min under the conditions of the assay. The temperature of the fermentor was maintained at 90° C for I hr to gelatinize and degrade starch to soluble dextrins. Then tap water was added to the fermentor. The volumes of tap water added at this stage were 1,328, 1,307, 1,315, 1,316, 1,309, and 1,337 ml for Newton wheat, Newton flour (83% extraction), Newton flour (70% extraction), Daws wheat, Daws flour (85% extraction), and Daws flour (70% extraction), respectively. The fermentor was cooled to 60° C, the pH was adjusted to 4.0, and to hydrolyze dextins 18 ml of Miles Diazyme L-100 glucoamylase (100 Diazyme units/ ml) was added. The suspension was incubated for 2 hr. The mixture was cooled to 30° C and adjusted to pH 4.5, and 500 ml of yeast (Saccharomyces cerevisiae) in the logarithmic growth phase containing an average of 5 million cells per milliliter was added. The yeast inoculum was made from 9 g of Fermivin dry yeast (G. B. Fermentation Industries, Des Plaines, IL), 0.3% yeast extract, 0.5% peptone, and 1.0% glucose in 500 ml of tap water. Each fermentation was stopped after 66 hr. Fractionation of Stillage Alcohol was distilled from the fermentor by steam, and the residue (stillage) was filtered through cheesecloth under suction (Fig. I). The thin stillage that passed through the cheesecloth was centrifuged at 45,000 rpm in a model T-I Sharples continuous centrifuge with a bowl having a 4.5-cm inside diameter. The solution that passed through the continuous centrifuge was designated distillers' solubles. The solids that remained in the bowl of the centrifuge were termed centrifuged solids. The materials that remained on the cheesecloth were the distillers' grains. The wet distillers' grains and wet centrifuged solids were dried overnight in a forced-air oven at 90° C or were freeze-dried. Ultrafiltration Two kinds of ultrafiltration apparatuses with different membranes were used. Amicon ultrafiltration cell model 52 (Amicon Corp., Lexington, MA) with two membranes 43 mm in diameter was used for most experiments. Each membrane is characterized by its nominal molecular weight cutoff; for example, 500 for UM05 and 10,000 for PM I 0; above these levels most species are retained by the membrane. Distillers' solubles (l0 ml) was