Sugar and ethanol production potential of sweet potato (Ipomoea batatas) as an alternative energy feedstock: processing and physicochemical characterizations

This study focuses on the processing, characterization, and sugar and ethanol production potential of red-fleshed sweet potatoes (RFSP) and white-fleshed sweet potatoes (WFSP). These feedstocks were used for the production of sugar; and bioethanol from its pulp by the action of five different microbes. The characterization of raw sweet potatoes and desired products of raw sugar, and bioethanol were carried out through proximate analyses, Fourier transforms infrared spectroscopic (FTIR) method, measurement of pol% by using a Refractometer, Polarimeter, Saccharimeter. The proximate analyses of feedstocks show the presence of a respectable amount of dry solids 25 ± 0.03g/100g with a lower amount of fat (0.025 ± 0.002) and ash (0.533 ± 0.076) contents make them promising crops for the production of sugar and ethanol. Comparatively, RFSP raw sugar ((o)Z: 95.25 ± 0.05) is considered purer than WFSP raw sugar ((o)Z: 94.6 ± 0.015). FTIR spectrums of the presently studied raw sugar and bioethanol have characteristic bands. It shows that the raw sugars products are rich in sucrose content, and confirms that the bioethanol was produced from the selected raw materials is at a satisfactory level. The efficiency of microbes was evaluated by taking a sample from the fermented wash to measure the residual sugar in ((o)Brix). Comparatively, fermented wash with sweet potato extracted yeast was found 14% Brix(o) (consume 86% of pulp) in RFSP, and 17% of Brix(o) (consume 83% pulp) in WFSP within 24 hours of fermentation. The alcohol level of bioethanol's produced from RFSP and WFSP pulps was tested using Ebuliometer and the result was found to be ranged 78 °C – 80 °C which is closer to the boiling point of absolute anhydrous alcohol (78.3 °C). Thus, the results of the present study proved that the sweet potato and its pulp are considered as a potential alternative sugar/energy feedstock.