Optimized synthesis of L-sorbose by C5-dehydrogenation of D-sorbitol with Gluconobacter oxydans

The optimization of L‐sorbose synthesis by regiospecific dehydrogenation of D‐sorbitol using Gluconobacter oxydans is reported. The current L‐sorbose production processes that are based on G. oxydans and other bacterial strains are suboptimal as to yield and rate of L‐sorbose synthesis. One reason for these problems is the toxicity that is induced by the substrate D‐sorbitol when used in concentrations of >10% (w/v). This phenomenon significantly limits the potentials of L‐sorbose production from an industrial point of view. The goal of this study was to develop a fast production process that yields L‐sorbose in stoichiometric amounts starting from D‐sorbitol concentrations that exceed 10% (w/v). A gradual improvement of the inoculum build‐up procedure, culture medium composition, and process parameters ultimately led to a theoretically maximal L‐sorbose productivity (200 g L−1 of L‐sorbose from 200 g L−1 of D‐sorbitol in 28 h of fermentation) using a Gluconobacter oxydans mutant strain that was selected under conditions of substrate inhibition. Because the D‐sorbitol/L‐sorbose bioconversion is used to mass‐produce vitamin C, the procedure reported here will contribute to a more efficient and more economic synthesis of vitamin C. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 69: 339–343, 2000.