Abstract
The ethanol production ability of baker’s yeast (Saccharomyces cerevisiae) and burukutu starter culture were examined on yam starch hydrolyzed with malts of maize and millet. Four substrate treatments which include yam starch (as control), yam starch hydrolyzed with millet malt (B), yam starch hydrolyzed with maize malt (C) and yam starch hydrolyzed with a mixture both millet and maize malt (D) were prepared in duplicate and made up to 600 ml. Baker’s yeast (4.40 g) was inoculated on one set of four while burukutu starter was inoculated on the other set of four and fermented for a period of four days at a temperature of 26°C. The pH was observed to drop as fermentation period increased, the highest ethanol yield of up to 74.5 g/Kg was obtained from starch hydrolyzed with maize malt and inoculated with baker’s yeast. Yam is a potential source of industrial scale ethanol production, there was a significant difference (p<0.05) between maize and millet malts in ethanol yield but between baker’s yeast and burukutu starter culture fermentation there was no significant difference (p<0.05), the interaction between malts and the inoculums was significant (p<0.05). Ethanol yield strongly depends on the hydrolysis of yam starch into fermentable sugar.
Highlights
Continuous search for renewable energy sources are ongoing
The specific gravity (SG) of the substrates decreased as fermentation began until it didn’t change any further after some days (Table 1) the greatest decrease in density was observe in wort treated with maize malt and bakers yeast with about 0.07 Kg/L deduction while the least was seen in the controls X1, X2 and B2 (0.02 Kg/L) this can be accounted for by higher starch content as compared to those treated with other malts
Decreased SG correlated with increased ethanol yield, it was observed to be highest after 24 hours and 48 hours, this agrees with Ref. [2] who observed steepest increase in ethanol production within the 24 hours, the authors attributed decreased ethanol production to inhibitory activities of both ethanol and by-products in the fermentation medium
Summary
Continuous search for renewable energy sources are ongoing. Key to this search is the discovery of biofuels which include biodiesels and bio-ethanol among others. Existing facts suggests that crude oil; the major source of organic fuel in Nigeria is gradually depleting and time will come when it will not sustain the nation or it will become scarce. The global collaborative fight against greenhouse gas emission necessitates eco-compatible and sustainable alternative fuel sources. Ethanol is a byproduct of the metabolic process of yeast [1]. Ethanol is produced by microbial or enzymatic fermentation; a process that converts sugars to ethanol and carbon (IV) oxide, shown below: C6H12O6→2 CH3CH2OH+2CO2
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