Acha (Digitaria exilis) Malt as a Source of Enzyme for Bio-Ethanol Production from Starchy Materials

Abstract

Three acha varieties were malted and their enzyme activities were compared with that of barley malt. During the malting, the maximum amylase activity was achieved on day 3 for white and black acha but in the case of brown acha, the maximum activity was obtained on  day 4. Under the optima malting conditions, all the three acha varieties gave higher amylase activity than barley malt. Of the three varieties of acha, white acha gave the highest glucoamylase activity (50 U/ml) and the least was exhibited by barley malt (26 U/ml). Application of malted acha as a source of enzyme for simultaneous hydrolysis and ethanol fermentation of two substrates (cassava and corn flour) was investigated under various conditions. Cassava flour yielded higher ethanol than corn flour under all the conditions investigated. Comparison of acha malt with koji enzymes for simultaneous hydrolysis and ethanol fermentation under various conditions showed that acha malt enzymes are superior to koji enzymes (microbial enzymes) under the three conditions investigated. Furthermore, regardless of the substrate used, gelatinization of starch improved ethanol productivity and yields. Incubating a mixture of raw starch and acha malt at 50^oC for 30 minutes before inoculation of yeast cells improved the ethanol production but the final ethanol concentration was not as high as the value obtained with gelatinized starch. These results have demonstrated that acha malt has great potential application in brewery and ethanol production industries.

Keywords: Acha malt, Koji enzymes, Bio-ethanol, Cassava flour, Corn flour