Productivity improvement in l-sorbose biosynthesis fedbatch cultivation of gluconobacter oxydans

Abstract

The effect of increased (100, 200 and 300 gl) initial sorbitol concentrations (S) was investi-gated in the sorbitol to sorbose bioconversion process. Batch cultivations with a S of 100,200 and 300 g1 were completed at 10, 14 and 24 h with a corresponding overall sorbose productivity of 10.1,14.3 and 12.4 gt h-l respectively. The decrease in sorbose productivity at So=300 gt 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 gt) sorbitol solution was added at a constant feed rate (0.2 I h-) in the exponential phase of growth. The Fed-batch culture initiated with So=225 gt exhibited an enhanced accumulation of sorbose (336.2 gt) but with a processing time of 24 h, and a productivity of 14.0 gt h-1.While, the fed-batch culture initiated with S= 100 gt accumulated 279.7 gt of sor-bose with an increase in productivity of 17.6 gt h-1 in 16 h.