The cetus process revisited: A novel enzymatic alternative for the production of aldose-free D-fructose

In the Cetus process crystalline D-fructose is produced from D-glucose via the intermediate 2-keto-D-glucose. Whereas the first step in the traditiona l process is catalyzed by the immobilized enzyme pyranose 2-oxidase, the en suing reduction is performed by catalytic hydrogenation. In an entirely enz ymatic variation of this process, soluble pyranose 2-oxidase from Trametes multicolor was employed. This biocatalyst could be efficiently stabilized u nder operational conditions by the addition of bovine serum albumin (BSA) t ogether with catalase which decomposes hydrogen peroxide formed as a by-pro duct. D-Glucose could be converted into 2-keto-D-glucose in yields above 98 %. When the biocatalyst together with both stabilizing agents was separated from the product solution by ultrafiltration, it could be reutilized for s everal subsequent batch operation cycles. 2-Keto-D-glucose thus obtained wa s quantitatively reduced to D-fructose by NAD(P)-dependent aldose reductase from Candida tenuis. Two different enzymatic systems were successfully emp loyed for the continuous regeneration of the coenzyme necessary in this rea ction. In this way, D-fructose essentially free of D-glucose can be prepare d by this simple and convenient method.