The use of cassava and sweet potato separately as raw materials for ethanol production in the recent past has been demonstrated. The search for the optimum processing conditions to hydrolyse and ferment sugars from the starches in cassava and sweet potato is well studied. The effects of substrate, temperature, enzyme types and concentrations, the reaction times of saccharification and fermentation were investigated for effect on ethanol yield. The objective of this work was to combine cassava and sweet potato as raw material to optimise the yield of ethanol for the combination. Selected cassava and sweet potato varieties were cultivated and harvested after 10 and 3 months, respectively. Liquefaction, saccharification and fermentation were carried out with Liquozyme SC DS, a combination of Spirizyme Fuel and Viscozyme L and Bio-Ferm XR (Lallemand) yeast, respectively. The combinations of cassava and sweet potato flours yield more ethanol than processing cassava and sweet potato flours separately. The best combination ratio of cassava and sweet potato, 1:1, resulted in the optimal ethanol yield of 16.2% v/v.
Key words: Cassava, sweet potato, optimization, ethanol yield, combination.
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