Screening of yeast isolates from flowers for effective ethanol production

Authors: ASMA CHAUDHARY, SHUICHI KARITA

Abstract: The use of alternative substrates to produce biofuel is a striking option nowadays. This study aimed to screen bioethanol-producing yeast strains. From different flowers, 65 yeasts were isolated. Twelve isolates assimilated glucose by liberation of CO₂ anaerobically. Out of these, only 5 yeast isolates fermented glucose in medium consisting of 0.8 g/L Mg²⁺ ions to produce 2.05 $\pm$ 0.03% ethanol. The selected five strains were identified as members of the genera Metschnikowia or Meyerozyma based on molecular characterization. Selected yeast strains were used for conversion of rice into bioethanol following dilute acid hydrolysis and fermentation. Consistent ethanol production was 1.80 $\pm$ 0.05% at days 2-4 by Metschnikowia cibodasensis Y34 and 2.20 $\pm$ 0.21% by Meyerozyma caribica Y42 at days 4-6 with a gradual decrease at the time of experiment termination (day 10). Metschnikowia cibodasensis Y34 and Meyerozyma caribica Y42 produced the highest ethanol at pH 3, i.e. 1.75 $\pm$ 0.14% at days 3 and 5 and 2.05 ($\pm$) 0.14% at days 1 and 3, respectively, upon incubation with different pH levels and 1% NaCl. Growth and ethanol production at pH 4 and 5 was close to that at pH 3, with a slight increase in production by Metschnikowia cibodasensis Y34 at pH 4 up to day 3.

Keywords: Ethanol-producing yeast, acid hydrolysis, Oryza sativa, bioethanol production, fermentation, biofuel

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