Production of the potential sweetener 5-ketofructose from fructose in fed-batch cultivation with Gluconobacter oxydans

[Display omitted] •5-Ketofructose (5-KF) is a potential low-calorie sweetener.•The sweet quality is good and without aftertaste, comparable to fructose.•Fructose dehydrogenase is overexpressed in G. oxydans to oxidize fructose to 5-KF.•5-KF production is characterized and a fed-batch fermentation process is developed.•Product concentrations up to 489 g/L and product yields up to 98% are reached. Sweeteners improve the dietary properties of many foods. A candidate for a new natural sweetener is 5-ketofructose. In this study a fed-batch process for the production of 5-ketofructose was developed. A Gluconobacter oxydans strain overexpressing a fructose dehydrogenase from G. japonicus was used and the sensory properties of 5-ketofructose were analyzed. The compound showed an identical sweet taste quality as fructose and a similar intrinsic sweet threshold concentration of 16.4 mmol/L. The production of 5-ketofructose was characterized online by monitoring of the respiration activity in shake flasks. Pulsed and continuous fructose feeding was realized in 2 L stirred tank reactors and maximum fructose consumption rates were determined. 5-Ketofructose concentrations of up to 489 g/L, product yields up to 0.98 g5-KF/gfructose and space time yields up to 8.2 g/L/h were reached highlighting the potential of the presented process.