Application Notes: Reflectometry – Total Sugar (Glucose and Fructose) in Potatoes

Reflectometric determination after enzymatic reaction with glucose-6-phosphate dehydrogenase and diaphorase


Cat. No. 116136 Reflectoquant® Total Sugar Test
Cat. No. 117246 Reflectometer RQflex® 20

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

Sample preparation:

Homogenize the potato in a blender (e.g. Ultraturrax). Weigh approx. 10 - 20 g of the mashed sample exactly into a 50-ml volumetric flask. Add approx. 40 ml distilled water and stir for approx. 10 minutes. Afterwards make up to the mark with distilled water. Filter through a folded filter.

french fries


Place 10 ml distilled water, 5 drops of reagent TS-1 and 1 ml filtrated sample in the test vessel and swirl. Press the reflectometer START key and simultaneously dip the test strip into the measurement sample (23 + 3 °C) for ca. 2 seconds, ensuring that both reaction zones are immersed. Allow excess liquid to run off via the long edge of the strip on to an absorbent paper towel. Insert the strip immediately into the strip adapter.

After 600 seconds the strip is measured 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® Total Sugar Test.)


Total sugar content [g/kg] = Measured value [mg/l] x 50 ml
Sample weight [g] x 100

Serial measurements:

After the first measurement, it is possible to run further measurements by pressing the START button. In this case, however, a stopwatch is required since the countdown function of the reflectometer is available only once per series.

Protect the reaction zones from light during the reaction time.

Results - comparison with enzymatic method:

Sample Reflectoquant® [g/kg] Enzymatic [g/kg]
1 15.4 17.3
2 5.7 6.4
3 0.4 0.4
4 < 0.2 0.1


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