Monday, April 30, 2007

Production of the polysaccharide curdlan on a corn dry-milling coproduct from ethanol fermentation

Thomas P. West and Beth Nemmers. Biology and Microbiology, South Dakota State University, Box 2104, Brookings, SD 57007

The utilization of the ethanol dry milling coproduct condensed corn distillers’ solubles for production of the polysaccharide curdlan was studied. Curdlan has several commercial uses including food and beverage applications. The polysaccharide is synthesized by Agrobacterium sp. ATCC 31749 in a nitrogen-limiting medium that contains an excess of carbon source. In this work, the bacterial cells were grown in a phosphate-buffered minimal medium (pH 6.8) that contained condensed corn distillers’ solubles as a source of carbon and nitrogen. The effect of supplementing 3% corn syrup to the medium as an additional carbon source was also investigated. Using shake flask cultures, the strain was grown for up to 120 hours at 30oC. A culture grown for 48 hours containing the same medium was used to inoculate each shake flask culture.  Gravimetric determinations were used to determine curdlan and biomass production. The strain could utilize the solubles to produce the polysaccharide in the medium containing no additional carbon source with the highest concentration being observed after 96-120 hours 30oC.  It did appear that carbon was limiting in the solubles because curdlan production could be further elevated after 120 hours at 30oC when the medium was supplemented corn syrup.  Biomass production by the strain grown on the corn syrup-containing medium generally was slightly lower compared to its production on the unsupplemented medium. In conclusion, it was possible to produce curdlan on the medium containing the dry milling coproduct condensed corn distillers’ solubles but additional carbon source in the medium stimulated higher polysaccharide production.