Application of solid-liquid TPPBs to the production of L-phenylacetylcarbinol from benzaldehyde using Candida utilis

The biotransformation of benzaldehyde and glucose to L-phenylacetylcarbinol (PAC) using Candida utilis was demonstrated in a solid-liquid two-phase partitioning bioreactor (TPPB) with the aim of reducing substrate, product, and by-product toxicity via sequestration. Previous work in the field had used octanol as the sequestering phase of liquid-liquid TPPBs but was limited by the toxic effects of octanol on C. utilis. To improve solvent selection in any future studies, the critical log P of C. utilis was determined in the current study to be 4.8 and can be used to predict biocompatible solvents. Bioavailability tests showed alkanes and alkenes to be non-bioavailable. As polymers are biocompatible and non-bioavailable, a wide range of commercially available polymers was screened and it was demonstrated that polymer softness plays a key role in absorptive capability. The polymer Hytrel G3548L was selected as the second phase to sequester benzaldehyde, PAC, and benzyl alcohol, with partition coefficients of 35, 7.5, and 10, respectively. With a 9% by volume partitioning phase, 13.6 g/L biomass of C. utilis achieved an overall PAC concentration of 11 g/L, a 1.9-fold improvement over the single-phase case. Benzyl alcohol concentration was 4.5 g/L, a 1.6-fold reduction. The volumetric productivity was 0.85 g/L h, a 1.2-fold improvement over the single-phase system. These results demonstrate a promising starting point for solid-liquid TPPBs for PAC production.