Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2016
Publication Date: 2/5/2017
Citation: Liu, K. 2017. Fractionation of condensed distillers solubles and compositional characterization of its co products. Journal of the American Oil Chemists' Society. 94(1):161-168.
Interpretive Summary: Fuel ethanol production in the United States has grown to be economically important. In 2015, US ethanol plants converted 5.2 billion bushels (132.1 million metric tons) of corn (about 38% of the total US supply) into an estimated 15.3 billion gallons (57.9 billion liters) of ethanol and 41 million metric tons of co-products as livestock feed. Over 90% of co-products was distillers dried grains with solubles (DDGS) resulting from a dry grind process. The process uses whole kernel grains (mostly corn) as a feedstock and creates two intermediate streams: distillers wet grains (DWG) and condensed distiller solubles (CDS). It is preferable to dry the two streams separately and generate two separate co-products, but CDS is very viscous and difficult to dry. The current industrial practice is to mix the two and dry them together to produce DDGS, which has been a global feed commodity. At present a typical dry grind ethanol plant earns roughly 27% of its gross revenue from the sale of co-products. Therefore, feed co-products represent an increasingly important share of profit opportunities for ethanol producers. Recently, three methods were developed at our laboratory to fractionate CDS into several sub-fractions that have unique composition and some of them are easier to dry than CDS. Therefore, the new co-product recovery methods not only solve the dewatering problem of CDS, eliminate the step of blending CDS with DWG for drying together into DDGS, and produce distillers dried grains (DDG) as a standalone product, but also create several fractions as new co-products. For exploring value added utilization of these new co-products and thus improving profitability of ethanol production, the present study was conducted to further characterize the new CDS fractions (except for the oil fraction) made by the three methods described earlier with respect to general composition, mineral profile, and amino acid composition. Recovery rates for mass and key nutrients, including protein, oil, ash, glycerol and other carbohydrates, in each fraction were also documented. Such information is vitally important for predicting feasibility and profitability of the new co-product recovery processes and improving utilization of the new co-products.
Technical Abstract: Condensed distillers solubles (CDS) was fractionated into a protein-mineral fraction and a glycerol fraction by a chemical method; protein and glycerol-mineral fractions by a physical method; and protein, mineral, and glycerol fractions by a physicochemical method. The coproducts from each method, along with CDS, were characterized for concentrations of key constituents (protein, oil, ash, glycerol and other carbohydrates), mineral profile, and amino acid composition. Recovery of mass and main constituents was also investigated. With the chemical method, about two-third of the mass went to the protein-mineral fraction, while by the physical method the equal amounts of mass went to the protein and glycerol-mineral fractions. Protein, minerals, and glycerol were mostly recovered into their respective fractions. CDS and its fractions contained six major minerals (Ca, Mg, P, K, Na, and S) and four trace ones (Cu, Fe, Mn, and Zn). Both chemical and physical treatments caused significant reduction of mineral contents (dry matter basis) in the protein or glycerol fraction. Several amino acids differed significantly in percent relative to total amino acids among fractions but the extent was not substantial for protein-rich fractions. These changes resulting from CDS fractionation are favorable for value added utilization of the new co-products.