Methods to recover value-added co-products from dry grind processing of grains into fuel ethanol

Authors: Liu, Keshun; Barrows, Frederic

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2013
Publication Date: 7/9/2013
Citation: Liu, K., Barrows, F. 2013. Methods to recover value-added co-products from dry grind processing of grains into fuel ethanol. Journal of Agricultural and Food Chemistry. 61.7325-7332.

Interpretive Summary: Fuel ethanol production in the United States and elsewhere is an important and growing industry. In 2012, the U.S. ethanol plants converted 114.3 million metric tons of corn (about 40% of total U.S. supply) into an estimated 50.3 billion liters of ethanol and 34.4 million metric tons of co-products as livestock feed. Of that production, 91.8% of ethanol facilities employed some variation of the dry-grind processing. In the dry-grind processing, the whole grain kernels are processed through several sequential steps, including; grinding, cooking, liquefaction, scarification, fermentation, distillation, and co-product recovery. This last step is an important one since the sale of co-products as livestock feed substantially increases the economic viability of ethanol plants. At the present, the major co-product of the dry grind process is the distillers dried grains with solubles (DDGS). In this communication, three methods are described to slightly modify the dry grind ethanol process. The three methods, based on chemical, physical and physicochemical principles, make it easier to reclaim distillers dried grains as a stand-alone product during ethanol production and at the same time produce a few new co-products, allowing producers to turn low-value DDGS into high-value ingredients. Furthermore, some of the new co-products have chemical compositions and nutritional values favorable for aquaculture feed, either as a protein ingredient or a mineral supplement. All of these developmental features could potentially boost profitability of the fuel ethanol industry.

Technical Abstract: Three methods were described to fractionate condensed distillers solubles (CDS) into several new co-products, including a protein-mineral fraction and a glycerol fraction by a chemical method; a protein fraction, an oil fraction and a glycerol-mineral fraction by a physical method; or a protein fraction, an oil fraction, a mineral fraction, and a glycerol fraction by a physicochemical method. Processing factors (ethanol concentration and centrifuge force) were also investigated. Results show that the three methods separated CDS into different fractions, with each fraction enriched with one or more of the five components (protein, oil, ash, glycerol and other carbohydrates), and thus having different targeted end uses. Furthermore, because glycerol, a hygroscopic substance, was mostly shifted to the glycerol or glycerol-mineral fraction, the other fractions had much faster moisture reduction rates than CDS upon drying in a forced air oven at 60°C. Thus, these methods could effectively solve the dewatering problem of CDS, allowing elimination of the current industrial practice of blending distiller wet grains with CDS for drying together and production of distiller dried grains as a standalone co-product in addition to a few new fractions.