ARS | Publication request: Conversion of starch from dry common beans (Phaseolus vulgaris L.) to ethanol

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 21, 2010
Publication Date: March 1, 2011
Citation: Nichols, N.N., Sutivisedsak, N., Dien, B.S., Biswas, A., Lesch, W.C., Cotta, M.A. 2011. Conversion of starch from dry common beans (Phaseolus vulgaris L.) to ethanol. Industrial Crops and Products. 33(3):644-647.

Interpretive Summary: This work demonstrated that starch from dry common beans could be efficiently fermented to ethanol using the same process and enzymes used for corn. Recognition of the health benefits of beans has led to focused interest in micronutrient content and functional properties of beans. Processing beans for selected high-value components will, however, necessitate development of uses for the other fractions, including starch and protein. Toward this end, starch from several varieties of dry beans was evaluated for potential conversion to ethanol. The average ethanol yield for the eight bean types examined was 92% of the theoretical maximum. Ethanol could be produced as a co-product to a higher-value use for another bean component, such as phytochemical extracts obtained from hulls. The protein fraction, if not extracted and marketed as an isolated product, could be collected after fermentation as a high-protein animal feed product.

Technical Abstract: Dry common beans (Phaseolus vulgaris L.) were evaluated for potential conversion of starch to ethanol. Eight varieties of beans with average starch content of 46% (db) were assayed in a laboratory-scaled process based upon the commercial corn dry grind fermentation process. Ethanol yield was 0.43-0.51 g ethanol/g glucose (0.19-0.23g ethanol/g beans). The average ethanol yield for the eight bean types was 92% of maximum theoretical yield, demonstrating that starch from beans could be efficiently converted to ethanol. Ethanol concentration obtained from 20% (w/w) solids loading was 3.5-4.4% (w/v). The residual fermentation solids contained, on a dry basis, 37.1-43.6% crude protein, 10.8-15.6% acid detergent fiber and 19.1-33.3% neutral detergent fiber.