Process parameters for biosurfactant production using yeast Meyerozyma guilliermondii YK32

Microbially produced biosurfactants are fast catching up due to their environment-friendly approach over chemical surfactants. But their commercial production is restricted due to poor economy of the production process which could be improved by using high yielding microbial strains and optimizing the process parameters. The present research was directed to optimize the biosurfactant production monitored in terms of oil displacement and emulsification (E₂₄) index, using a promising yeast Meyerozyma guilliermondii YK32. Maximum oil displacement equaling 7.5 cm was obtained with olive oil at 8% (v/v) concentration as carbon source under shaking conditions (150 rpm). Diesel being a complex hydrocarbon was not utilized easily by yeast and showed poor biosurfactant production. Yeast extract at 1.5% (w/v) concentration yielded maximum biosurfactant as evident from maximum oil displacement and E₂₄ index equal to 8.1 cm and 52.6%, respectively. Sodium chloride at the rate of 3% (w/v) supported maximum oil displacement (8.8 cm) using the production broth containing optimized carbon and nitrogen sources. Any increase beyond this level negatively influenced the biosurfactant production. The yield was at its maximum at 30 °C as a shift in temperature either to 35 °C or 25 °C decreased the oil displacement from 8.8 to 5.2 or 7.6 cm, respectively. At 40 °C, oil displacement was decreased to 2.5 cm. Biosurfactant production appeared to be sensitive to varying pH as evident from the E₂₄ index as high as 67.3% at pH 6.0 as compared with 60.2%, 60.1%, and 52.4% at pH 5.0, 5.5, and 7.0, respectively. Yeast biomass yield equivalent to 10.3 g/L and 8.3 g/L was recorded at pH 6 and 7, respectively, during the production process. Elimination of shaking reduced the E₂₄ index from 67.3 to 34.8% under optimized conditions.