Bioethanol Production from Decaying Oranges and Pineapple Juice Using Ethanol Tolerant-Yeast

Scientists across the globe ought to harness ways of getting alternative sources of energy which will be renewable, sustainable, efficient, eco-friendly, and cost effective because of the global energy crises owing to the cost of production, transportation and distribution of fossil fuel products. In Nigeria, decaying fruits always constitute a major environmental pollution during the harvesting season. This study screened, selected the best starter, and produced bioethanol from the juice obtained from decaying oranges and pineapple through the process of fermentation and distillation. Samples were collected from different locations within Ile-Ife and transported aseptically to the Laboratory. Microbiological and physicochemical assessment of the isolated strains were on yeast maintenance media. The cell biomass, pH, temperature, brix level, titratable acidity, specific gravity and ethanol yield were monitored during fermentation from day zero to day fourteen. Screening of the isolates obtained from a previous study was carried out to select the best starter for the production of bioethanol.

S.cerevisae and K. marxianus and showed efficient physico-chemical attributes from the screening of the yeast isolates; a temperature of 30oC and pH 6 was the optimum for the growth of isolates tolerating 20% v/v absolute ethanol. Cultures were inoculated singly and in combination, S. cerevisiae gave the highest reduction in brix level from 2.2o at the onset and it reduced to 0.3o at the 21st day of fermentation while the least reduction was seen in K. marxianus. Mixed culture of S. cerevisiae and K. marxianus gave the highest reduction in brix level from 2.0o at the onset to 0.1o, pH reduced from 4.7- 3.3 while the cell biomass increased, and the temperature increased from 30oC to 34.5oC at the end of fermentation. Titratable acidity in the fermenting fruits juice increased from 0.23 to 1.76, the specific gravity reduced while the alcohol content increased from zero to 25.63 as the fermentation progressed and a reduction on day 21 (1.67) was observed.

The use of decaying plant biomass or fruit waste can be a rich and cheaper source of substrate for different yeasts strains endogenous to the biomass for the production of environmental-friendly biofuel. This can also be employed as a waste management option and an alternative solution to environmental pollution and the global energy crises.