Isolation, characterization of ethanol-tolerant yeast from decaying oranges and pineapples for the production of bioethanol: A waste management option

Abstract

The increase in population has led to a high demand for petroleum, a nonrenewable fossil fuel; excessive use of which results in global  warming causing health and environmental problems. Therefore, there is a need for urgent replacement with renewable energy such as  Bioethanol. The study focuses on isolating, identifying, and confirming ethanol-tolerant yeasts from decaying oranges and pineapples  obtained from local markets within the Ibadan Metropolis. Standard morphological, biochemical, analytical profile index (API), and  physicochemical tests were carried out on the yeasts and ethanol produced respectively. The fruits were crushed, juice extracted and  yeasts isolated with Yeast Extract Agar (YEA) and screened for ethanol, NaCl, and antibiotics tolerance. The brix level, titratable acidity, pH,  and specific gravity of the ethanol produced were determined during fermentation from day zero to fourteen. The yeasts isolated  were Candida valida, Pichia meri, Saccharomyces cerevisiae, Kluveromyces fragilis, and K. marxianus. The pH and TTA were monitored  from day 0 to day 14, a decrease in pH from 4.57 to 3.07 and an increase in TTA from 0.03 to 0.51 was observed as fermentation  progressed. There was a significant reduction in reducing sugar level (brix) from 1.10 to 0.20; and specific gravity from 1.036 on day 0 to 1.005 on day 14. The lower the specific gravity, the higher the alcohol content. This means that the alcohol content increases as the  specific gravity reduces. Moreover, the pH and the specific gravity reduced, and the ethanol content increased with fermentation time.  This research concluded that decaying oranges and pineapples can serve as substrates for isolating of ethanol-tolerant yeasts and  producing bioethanol, thus presenting a viable waste management solution.