SIMULTANEOUS ENZYMATIC-SYNTHESIS OF GLUCONIC ACID AND SORBITOL - CONTINUOUS PROCESS-DEVELOPMENT USING GLUCOSE-FRUCTOSE OXIDOREDUCTASE FROM ZYMOMONAS-MOBILIS

The production of sorbitol and gluconic acid by isolated glucose-fruct ose oxidoreductase (GFOR) from Zymomonas mobilis has been studied in a convective, 100-mL loop reactor with tangential ultrafiltration Using a dilution rate of 0.04/h and 5 kU/L GFOR, substrate conversion (3 M sugar) in a single stage was >85%, and productivities of 126 g sorbito l/(L.d) were obtained. At a constant recycle rate (3/min) and a membra ne area of 50 cm(2), the dilution rates land thus productivities) were however limited by a more than 30-fold reduction of the permeate flow in the presence of high sugar and protein concentrations (5 g/L). Pro tein was added, together with 10 mM dithiothreitol, to improve the sta bility of GFOR during substrate turnover and crossflow filtration, thu s leading to a stable operation of the enzyme reactor for at least 5 d .