Effect of Starch Granule Morphology on Production of Bioethanol from Cassava and Sweet Potato

Abstract. The need for renewable biofuels alerted by increasing global energy demand which failed to be met with fossil fuels has led to a search for suitable alternatives like bioethanol to meet this great challenge. In this study, starch was extracted separately from both cassava (Manihot esculenta Crantz) and sweet potato (Ipomea batatas Lam), hydrolysed with α-amylase followed by fermentation of the hydrolysates at room temperature with bakers' yeast at varying fermentation durations (between 24 and 120 h) and pH values (between 4.5 and 6.5). From the experimental results, the optimum fermentation duration is 48 h for sweet potato and 120 h for cassava, while the optimum pH is 4.5 and 6.5 for sweet potato and cassava respectively. These results show that although both duration and pH of fermentation affect the production of ethanol; their effects are not independent of the presence of readily fermentable sugars in the fermenting mash which is predicated on the granule morphology of the starch in the feedstock.