Nutritional value of sweet potato residue following fermentation for ethanol

Two sweet potato cultivars. Centennial, an orange-flesh type, and TG-75-96-1, an industrial white cultivar, were comminuted and allowed to ferment to produce ethanol. An enzyme alpha-amylase, was used to hydrolyze starch to increase the concentration of fermentable sugars. Saccharomyces cerevisiae was used to ferment the sugars to ethanol. Fermentation was completed in two weeks at 21.1-23.9°C. Ethanol production was 2.02% for the orange and 1.73% for the white sweet potatoes. Analysis of the fermented residue indicated that the percentage protein was increased for Centennial, from 4.7% to 7.0%, and for the white-fleshed cultivar, from 4.3% to 5.1%. The amount of fat, crude fiber, caloric content, calcium and iron increased also. The essential amino acid (EAA) analysis showed no significant change in amino acid content and that isoleucine was the limiting amino acid for both cultivars. Centennial was found to be significantly more nutritious than the white cultivar in terms of the B-vitamins and vitamin C. The white cultivar, however, contained a significantly greater solids content indicating a potentially higher yield of ethanol.