Baker's yeast mediated biotransformation of geraniol into citronellol using a continuous-closed-gas-loop bioreactor (CCGLB) system

The kinetics of the biotransformation of geraniol into citronellol by the resting cells of Saccharomyces cerevisiae (baker's yeast type-II) was investigated in a continuous-closed-gas-loop bioreactor (CCGLB). Geraniol, which has high vapour pressure, high volatility and low solubility in aqueous medium, is highly suitable to be used in this system. Various operating parameters which affect the reduction reaction were investigated. The optimal conditions were; pH 7, agitation rate of 350 rpm, substrate flow rate of 8 L/min and glucose concentration of 50 g/L. The gas loop led to a maximum citronellol concentration of 2.38 g/L with the specific activity of 7.90 U/gcell, which were apparently higher than that of the values obtained using conventional systems. The CCGLB system also has the advantage of in situ product removal and can be readily utilized in large-scale production.

► The CCGLB system gives an advantage of in situ product removal.
► Gas phase biotransformation promotes better mass transfer between gas and liquid phases.
► High substrate flow rate gives a positive effect to the rate of reaction.
► High agitation leads to an excessive foaming inside the CCGLB.