(342e) Ethanol Production From Waste Sweet Potato Using Recombinant Zymomonas Mobilis Strains

Ethanol production from waste sweet potatoes, which are left in the fields and cannot be marketed for various reasons, has been investigated. Sweet potatoes collected from a family-owned farm in Texas contain 4.35% sucrose, 2.68% glucose, and 2.21% fructose, respectively. However, since the dry mass content is only 19.4%, the average sugar content based on the dry biomass is close to 50%. Other component in the dry biomass is mainly starch, which can be effectively converted to monosaccharides, mainly glucose and fructose, using amyloglucosidase as the enzyme at 55 oC. Two strains of recombinant Zymomonas mobilis, 8b and AX101 from National Renewable Energy Laboratories, have been tested, to convert the enzyme treated sweet potatoes to ethanol. The capacity of these two strains to converting ethanol from four sugars, e.g. glucose, xylose, fructose and sucrose, has first been evaluated individually. The results show that, these two strains have very different capacities in converting those sugars to ethanol. Fermentation experiments have been conducted in a 1 L fermentor at 30 oC, average pH 6 and anaerobic condition, using the enzyme treated sweet potato as the raw material. More than 90% of the sugar can be converted to ethanol within 24 hours.