Conversion of L‐sorbose to L‐sorbosone by immobilized cells of Gluconobacter melanogenus IFO 3293

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Abstract
Gluconobacter melanogenus IFO 3293 cells capable of converting L‐sorbose to L‐sorbosone were immobilized in polyacrylamide gel. The preferred polymer composition for high activity and stability was determined to contain a total monomer concentration of 7.2% and 16.6% crosslinking agent. No significant differences in optimal conditions for conversion, e. g., pH and temperature, were found in comparison with free cell suspensions. However, in the absence of L‐sorbose, the thermal stability of immobilized cells was lower. After the initial loss, the conversion activity of immobilized cells increased, possibly due to lysis, and this increase was related to the polymerization conditions and the incubation temperature for the L‐sorbose conversion. The enzymatic activity and stability of the immobilized cells also depended on the physical form of the gel and the aeration levels. Addition of electron acceptors or addition of L‐sorbosone to the medium reduced, while addition of neomycin, ampicillin, chloramphenicol, and tetracycline increased the stability of the enzymatic activity.