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Abstract
D-Glucose and D-fructose are present in honey, wine and beer, and in a range of other foodstuffs such as bread, pastries or chocolate. Both sugars can occur as a monosaccharide or in di-, oligo- and polysaccharides. To validate the performance of the Enzytec™ Liquid D-Glucose/D-Fructose test kit for the determination of D-glucose and D-fructose in food and beverages such as fruit and vegetable juices, soft drinks, wines, and beer. The method is based on enzymes which are part of a prepackaged kit that contains 3 ready-to-use components. Both sugars are phosphorylated by a hexokinase. Glucose-6-phosphate (G-6-P) and NAD are converted to gluconate-6-phosphate and NADH. NADH is measured at 340 nm. Phosphoglucose isomerase converts fructose-6-phosphate to G-6-P which in turn is converted to gluconate-6-phosphate and NADH. The test is specific to D-glucose and D-fructose and shows no side activities or interferences with the exception of mannose and sulphite that interfere at 5.1 and 1.25 g/L or more, respectively. The measurement range is from 6.1 to 2000 mg/L for D-glucose and 5.6 to 1000 mg/L for D-fructose (100 µL test volume). Trueness was evaluated using NIST SRM 3282 (cranberry juice) and one reference wine. The recoveries ranged from 101 to 102%. Spiking of wine, beer, soft drinks and juices resulted in recoveries between 93 and 105%. Intermediate precision is below 6% for concentrations at 25 mg/L and below 4% for higher concentrations. For automation, three applications with different test volumes and different measurement ranges were validated. Linearity is given from 5.0 up to 10000 mg/L for the sum of both sugars. The method is robust and accurate for manual and automated applications and was approved as AOAC Official Method of Analysis℠. The ready-to-use components of the test kit have a shelf of at least 29 months.
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