Biotransformation of 2-phenylethanol to phenylacetaldehyde in a two-phase fed-batch system

Phenylacetaldehyde (PA) can be produced by the oxidation of 2-phenylethanol (PE) through biotransformation. In order to prevent substrate and product inhibitions and the transformation of the PA to phenylacetic acid (PAA), utilization of a two-phase system is very attractive. Gluconobacter oxydans B-72 was used as the microorganism and iso-octane as the solvent. The effect of initial substrate concentration on the PA production was investigated in single- and two-phase systems. In the single-phase system, substrate inhibition occurred above 5 g/l, and in the two-phase system, above 7.5 g/l. Substrate inhibition kinetics were also studied in the two-phase system and kinetic constants were determined as r_max=0.64 g/l min, K_M=8.15 g/l, K_PA=2.5 g/l. Because it was observed that two-phase system is insufficient to remove the substrate inhibition effect, fed-batch operation was utilised in this study. For 7.5 g/l of PE, 1.65, 3.85, and 7.35 g/l of PA were obtained in the single-phase, two-phase, and two-phase three fed-batch systems, respectively. Effect of biotransformation time, initial substrate concentration, agitation speed, and fed-batch number on the PA production was investigated in a two-phase fed-batch system by the response surface methodology (RSM). The optimum values were found as 3 fed-batch number, 2.75 g/l initial substrate concentration, 150 rpm agitation speed, and 65 min of one batch biotransformation time. In order to verify these results, an experiment was performed at these optimum conditions and 7.10 g/l of PA concentration was obtained.