Application Notes Reflectometry – Glucose in Juices

Reflectometric determination after reaction with glucose oxidase and peroxidase

Glucose in Juices (Reflectometry)Reagents

Cat.No. 116720 Reflectoquant® Glucose Test

Cat.No. 117246 Reflectometer RQflex® 20

This application note pertains to RQflex® 20 and all discontinued instruments (RQflex® 10, RQflex® plus)


Sample preparation

Dilute the sample in a suitable way by adding distilled water (for dilution factors see the table below). Mix 1 mL of juice with distilled water in either a 500-mL or 1000-mL volumetric flask and make up to the final volume (dilution factor 500 or 1000).


Press the reflectometer START key and simultaneously place the test strip into the prepared sample solution (15 - 30 °C) for 15 seconds, ensuring that both reaction zones are immersed. Remove the strip and allow excess liquid to run off via the long edge of the strip on to an absorbent paper towel. Wait 60 seconds and then measure the strip in the reflectometer. The value [mg/l] will be stored automatically. (Please refer to the RQflex® operating instructions and the package insert of the Reflectoquant® Glucose Test.)


Glucose content [mg/l] = Measured value [mg/l] x dilution factor


Results – comparison with enzymatic method

Sample Dilution factor Reflectoquant® [g/L] Enzymatic [g/l]
Orange juice 1   500 25.6 25.3
Orange juice 2   500 25.0 26.5
Multivitamin juice   500 28.3 27.7
Apple juice 1   500 32.5 33.0
Apple juice 2   500 28.8 27.5
Grape juice (red) 1000 75.6 78.0
Carrot juice   500 16.0 16.0
Coca Cola 1000 54.0 48.0


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