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

The effect of increased (100, 200 and 300 gl(-1)) initial sorbitol concentrations (S0) was investigated in the sorbitol to sorbose bioconversion process. Batch cultivations with a S0 of 100, 200 and 300 gl(-1) were completed at 10, 14 and 24 h with a corresponding overall sorbose productivity of 10.1, 14.3 and 12.4 gl(-1) h(-1) respectively. The decrease in sorbose productivity at S0=300 gl(-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 gl(-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 S0=225 gl(-1) exhibited an enhanced accumulation of sorbose (336.2 gl(-1)) but with a processing time of 24 h, and a productivity of 14.0 gl(-1) h(-1). While, the fed-batch culture initiated with S0=100 gl(-1) accumulated 279.7 gl(-1) of sorbose with an increase in productivity of 17.6 gl(-1) h(-1) in 16 h.