A simple, quick enzymatic spectrophotometric assay specific for dextran

An enzymatic assay was developed for the direct, exclusive quantification of dextran in raw juice from sugarbeet, using the method of standard additions and dextran of molecular mass 2,000,000. Ethanol precipitation and a subsequent ethanol rinse was used to remove sucrose. Dextran was resuspended in citrate buffer and digested with dextranase. Isomaltose was then quantified using a Roche diagnostic glucose test kit, with an additional isomaltase solution. Reduction of NADP+ to NADPH was monitored at 340 nm, producing the detectable signal. The assay shows excellent linearity (r2 = 0.98 to 0.99) and can be used to determine dextran concentrations from 50 to 400 mg/L in raw juice, using 10 mL samples. Larger sample volumes can be used to detect lower dextran concentrations. Sucrose and starch augment the signals, but neither levan nor pectin shows any interference. The assay responds the same to dextrans of molecular mass 9,500, 500,000 and 2,000,000, can be performed in 3 to 4 h, is relatively simple and requires no expensive equipment or hazardous chemicals.