Productivity improvement in l-sorbose biosynthesis by fedbatch cultivation of Gluconobacter oxydans

The effect of increased (100, 200 and 300 g l −1) initial sorbitol concentrations (S 0) was investigated in the sorbitol to sorbose bioconversion process. Batch cultivations with a S 0 of 100, 200 and 300 g l −1 were completed at 10, 14 and 24 h with a corresponding overall sorbose productivity of 10.1, 14.3 and 12.4 g l −1 h −1 respectively. The decrease in sorbose productivity at S 0=300 g l −1 was attributed to the inhibition by sorbitol of culture growth and product formation. In order to eliminate substrate inhibition, two identical fed-batch cultivations were performed in which a highly concentrated (500 g l −1) sorbitol solution was added at a constant feed rate (0.2 l h −1) in the exponential phase of growth. The Fed-batch culture initiated with S 0=225 g l −1 exhibited an enhanced accumulation of sorbose (336.2 g l −1) but with a processing time of 24 h, and a productivity of 14.0 g l −1 h −1. While, the fed-batch culture initiated with S 0=100 g l −1 accumulated 279.7 g l −1 of sorbose with an increase in productivity of 17.6 g l −1 h −1 in 16 h.