RAPID AND SIMPLE DETERMINATION OF D-GLUCOSE, D-FRUCTOSE AND SUCROSE IN FOOD BY COMBINATION OF QUINONE-DEPENDENT DEHYDROGENASE REACTIONS AND SELF-DRIVEN COULOMETRY

A new method for determination of D-glucose, D-fructose and sucrose was developed by combining quinone-dependent dehydrogenase reactions and self-driven coulometry and applied for determination of sugars in food. Enzyme reaction was carried out in a mixture consisting of phosphate buffer (pH 6.5), ubiquinone-0 (Q(0)), quinone-dependent glucose dehydrogenase or fructose dehydrogenase. An aliquot of the reaction mixture was then added to the self-driven coulometric cell to determine the amount of reduced Q(0) by coulometry. In a range of 0.1 to 6% (w/v) of D-glucose or D-fructose, the measured total charge was correlated with sugar concentration and corresponded to the theoretical total charges, suggesting that these sugars were determined without calibration. In case that glucose dehydrogenase and invertase were used, sucrose was determined. D-glucose, D-fructose and sucrose in various foods were determined by this method and the results were correlated with those determined by high-performance liquid chromatography and enzymatic method. Coefficient of variation of ten trials was about 2%. Total concentration of the three sugars was also rapidly determined and the results were correlated with the Somogyi's method (r=0.9983).