Abstract
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.
Highlights
Corn, sugar cane and wheat are major crops used globally to produce ethanol (Zabed et al, 2016; Li et al, 2016; Gupta and Verma, 2015, McMurry, 2015; Vollhardt and Schore, 2014; Boundy et al, 2011)
Several studies demonstrate the use of cassava and sweet potato as raw materials for ethanol production (Costa et al, 2018; Martinez et al, 2018; Pereira et al, 2017; Schweinberger et al, 2016; Archibong et al, 2016; Swain et al, 2013; Oyeleke et al, 2012; Ademiluyi and Mepba, 2013; Ocloo and Ayenor, 2010)
Sika bankye and Apomuden were selected for the study because they are improved cassava and sweet potato varieties in Ghana that have higher starch and lower fresh root moisture content compared to the other cassava variety (Ampong) and sweet potato variety (Tuskiki) used and analysed in earlier study (Komlaga, 2018)
Summary
Sugar cane and wheat are major crops used globally to produce ethanol (Zabed et al, 2016; Li et al, 2016; Gupta and Verma, 2015, McMurry, 2015; Vollhardt and Schore, 2014; Boundy et al, 2011). The potential of cassava is significant because it offers the cheapest source of food calories and the highest yield per unit area (Duvernay et al, 2013; Lee et al, 2012) It has multiple roles as a famine reserve, food and cash crop, industrial raw material and livestock feed (Amarachi et al, 2015). The over seventy (70) million litres of ethanol imported into Ghana for the various industries in 2016 (Ghana Business News, 2017) could have been produced in Ghana using the excess cassava as raw material. It has been reported that some industrial sweet potato breeding lines developed could produce ethanol yields of 4500 to 6500 L/ha compared to 2800 to 3800 L/ha for corn (Duvernay et al, 2013; Ziska et al, 2009)
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