L-Sorbose production in a continuous fermenter with and without cell recycle

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The kinetics of continuous l-sorbose fermentation using Acetobacter suboxydans with and without cell recycle (100%) were investigated at dilution rates (D) of 0.05, 0.10, 0.15 and 0.3 h−1. The biomass and sorbose concentrations for continuous fermentation without recycle increased as the dilution rate was increased from 0.05 to 0.10 h−1. A maximum biomass concentration of 8.44 g l−1 and sorbose concentration of 176.90 g l−1 were obtained at D=0.10 h−1. The specific rate of sorbose production and volumetric sorbose productivity at this dilution rate were 2.09 g g−1 h−1 and 17.69 g l−1 h−1. However, on further increasing the dilution rate to 0.3 h−1, both biomass and sorbose concentrations decreased to 2.93 and 73.20 g l−1 respectively, mainly due to washout of the reactor contents. However, the specific rate of sorbose formation and volumetric sorbose productivity at this dilution rate increased to 7.49 g g−1 h−1 and 21.96 g l−1 h−1 respectively. Continuous fermentation with 100% cell recycle served to further enhance the concentration of biomass and sorbose to 28.27 and 184.32 g l−1 respectively (in the reactor at a dilution rate of 0.05 h−1). Even though, there was a decline in the biomass and sorbose concentrations to 6.8 and 83.40 g l−1 at a dilution rate of 0.3 h−1, the specific rates of sorbose formation and volumetric sorbose productivity increased to 3.67 g g−1h−1 and 25.02 g l−1 h−1.