Malt hydrolysis of sweet-potatoes and eddoes for ethanol production

Abstract

In the Caribbean the main root crops produced are cassava, sweet-potatoes, eddoes, dasheen and yam. The production of ethanol from these starchly substrates first requires the hydrolysis of the starch into simpler sugars. Hydrolysis can be performed enzymatically or by means of acids. The root crops selected for study were sweet-potatoes ( Ipomoea batatas) and eddoes ( Colocasia antiquorum esculenta var. globulifera). They were hydrolysed using the enzymes contained in malt. The optimum malt percentage for the conversion of cooked sweet-potato was in the range 8–10% with a corresponding reaction time of 60 min at the set saccharification temperature of 66°C. The optimum malt percentage for the conversion of eddoes was 8% with the other conditions of time and temperature being as for sweet-potatoes. The sugars obtained under the above conditions were 5.6 and 5.4% (w/v) for sweet-potatoes and eddoes, respectively. The corresponding starch conversions were 88 and 92%. Fermentation of the above hydrolysates gave alcohol in the region of 2.3 and 2.2% (v/v) for sweet-potatoes and eddoes, respectively. The conversion of sugar to alcohol was 91 and 89%. A pre-determined quantity of malt was then added prior to cooking and the hydrolysis procedure was followed using the optimum malt percentages. As the solid/liquid ratio increased from 0.3 to 0.5, the percentage sugars (w/v) increased from 7.53 to 10.72% and from 6.29 to 9.35% for sweet-potatoes and eddoes, respectively. The corresponding starch conversions were 96 and 95%.