Biooxidation of 2-phenylethanol to phenylacetic acid by whole-cell Gluconobacter oxydans biocatalyst immobilized in polyelectrolyte complex capsules

A high-performance biocatalyst in the form of encapsulated cells of Gluconobacter oxydans have been developed for production of phenylacetic acid (PAA) as a natural flavor component. Polyelectrolyte complex (PEC) capsules consisting of sodium alginate, cellulose sulfate, poly(methylene-co-guanidine), CaCl2, and NaCl were used for highly controlled and mild encapsulation of cells. Utilization of encapsulated G. oxydans cells was a significant improvement on existing data on operational stability of cells and cumulative product concentration during biocatalytic production of PAA from 2-phenylethanol. Concerning operational stability, encapsulated cells were active over 12 cycles with a high biotransformation rate, while free cells were inactive after 7 cycles of use. The biocatalytic properties of encapsulated G. oxydans were tested in a bubble column reactor over 7 days with a final cumulative product concentration of 25 g/L. High cell viability (90%) was observed within PEC capsules by confocal laser scanning microscopy, performed before and after repetitive PAA production in the bubble column reactor. The surface microstructure of fully hydrated capsules with and without G. oxydans cells was investigated and compared using an environmental scanning electron microscope.