Sucrose (Saccharose) in Soft Drinks

Reflectometric determination after enzymatic conversion.

Experimental Method

Sucrose (saccharose) is cleaved by sucrose phosphorylase into fructose and glucose-1-phosphate. The latter is converted by phosphoglucomutase into glucose-6-phosphate. This is in turn oxidized by NAD under the catalytic effect of glucose-6-phosphate dehydrogenase to gluconate-6-phosphate. In the presence of diaphorase the NADH formed in the process reduces a tetrazolium salt to a blue formazan that is determined reflectometrically.

Reagents, Instruments and Materials

Test Kits

• Sucrose (Saccharose) Test Method: reflectometric with test strips and reagent 0.25 - 2.50 g/l Reflectoquant^® (1.16141)

Instruments

• Reflectometer RQflex^® 20 Reflectoquant^® (1.17246)*

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

Sample preparation

Dilute the sample depending on the anticipated sucrose content, e. g. for a 1:100 dilution, pipette 0.5 ml of sample into a 50-ml volumetric flask and make up to the mark with distilled water. The measurement results should preferably lie in the middle of the measuring range. It may be necessary to repeat the dilution step with a further dilution.

Instrumental Analysis

• Place 10 ml of distilled water, 5 drops of reagent Sa-1, and 1 ml of correspondingly diluted sample in the test glass and swirl.
• Press the start button of the reflectometer and at the same time immerse the test strip with both reaction zones into the measurement sample (20 - 26 °C) for approx. 2 seconds.
• Allow excess liquid to run off over the long edge of the strip onto an absorbent paper towel.
• Immediately insert the test strip into the strip adapter.
• The test strip is measured in the reflectometer after 300 seconds.

The measurement value [g/l] is saved automatically. (See the operating manual for RQflex^® and the instruction for use for Reflectoquant^® Sucrose (Saccharose) Test.)

Serial measurement

After the first measurement, any number of further measurements can be made by pressing the start button. This, however, requires the use of a stopwatch since the countdown function of the reflectometer is available only for the first measurement. The detection zones of the test strip must be appropriately protected from light during the reaction time.

Calculation

Sucrose content [g/l] = measurement value [g/l] x dilution factor

Results