Synthesis of Cinnamyl Alcohol from Cinnamaldehyde with Bacillus stearothermophilus Alcohol Dehydrogenase as the Isolated Enzyme and in Recombinant E. coli Cells

The synthesis of the aroma chemical cinnamyl alcohol (CMO) by means of enzymatic reduction of cinnamaldehyde (CMA) was investigated using NADH-dependent alcohol dehydrogenase from Bacillus stearothermophilus both as an isolated enzyme, and in recombinant Escherichia coli whole cells. The influence of parameters such as reaction time and cofactor, substrate, co-substrate 2-propanol and biocatalyst concentrations on the bioreduction reaction was investigated and an efficient and sustainable one-phase system developed. The reduction of CMA (0.5 g/L, 3.8 mmol/L) by the isolated enzyme occurred in 3 h at 50 °C with 97 % conversion, and yielded high purity CMO (≥98 %) with a yield of 88 % and a productivity of 50 g/g_enzyme. The reduction of 12.5 g/L (94 mmol/L) CMA by whole cells in 6 h, at 37 °C and no requirement of external cofactor occurred with 97 % conversion, 82 % yield of 98 % pure alcohol and a productivity of 34 mg/g_{wet cell weight}. The results demonstrate the microbial system as a practical and efficient method for larger-scale synthesis of CMO.