Color Determination of White Sugar Solution with a Color Index up to 50 IU Based on ICUMSA^® Color GS2-10 (2024)

Introduction

The measurement of degrees Brix and solution color is routinely required in sugar manufacturing industries, where these parameters are used to grade product concentration, assess product quality, and support blending operations. The development of color in sugar products is attributed to specific stages of the manufacturing process. During refining, progressive removal of color occurs as raw sugar undergoes additional processing steps, and the pigmentation of the final product reflects the extent of refining to which it has been subjected. The refining process can therefore be regarded as a sequence of operations in which higher-colored raw sugar with lower market value is converted into low-colored refined white sugar with higher market value.¹

To support this evaluation, several scales for the measurement of degrees Brix and color are used in the food industry. ICUMSA^® (International Commission for Uniform Methods of Sugar Analysis) is recognized as the global body responsible for analytical methods applied in the sugar sector. Within this framework, raw sugar obtained from the initial production stage is characterized by very high color values and requires refinement and purification prior to consumption. Brown sugar and natural sugar represent partially purified forms of raw sugar that retain relatively high color values. Further purification yields refined and white sugars with substantially lower color values.

Analytical determination of color in these products is performed using standardized procedures. The method titled “Sugar color” is based on ICUMSA^® Method GS2-10 (2024). Full procedural details are provided in the Official ICUMSA^® Method, although updated versions may exist. This method is applied to solutions of crystalline white sugar, icing sugar, sugar syrup with color indices up to 50 IU (ICUMSA^® Units). In the analysis, the sample under investigation is dissolved in water. Subsequently, the dry mass is measured by refractometry, and the absorption of the prepared sample is determined photometrically at 420 nm, with the results being used to calculate the ICUMSA color.

Experimental

Method

In the analysis, the sample under investigation is dissolved in water. Subsequently the dry mass is measured by refractometry, and the absorption of the prepared sample is determined photometrically at 420 nm, with the results being used to calculate the ICUMSA^® color.

The method is based on the ICUMSA^® Method GS2-10 (2024).²

Applicable Sample

Sugar with a color index up to 50 IU (e.g., crystalline white sugar, icing sugar, sugar syrup).

Instruments, Reagents, and Auxiliaries

Instrument(s) & Devices

For the measurement one of the following Spectroquant^® photometers is necessary

• Spectroquant^® VIS Spectrophotometer Prove 100 plus (1.73026)
• Spectroquant^® UV/VIS Spectrophotometer Prove 300 plus (1.73027)
• Spectroquant^® UV/VIS Spectrophotometer Prove 600 plus (1.73028)

This application note pertains to the above listed photometers and all discontinued instruments from the Spectroquant^® Prove series.

Software for Data transfer

• Optional Spectroquant^® Prove Connect to LIMS software package (Y.11086) to transfer your data into an existing LIMS system.

Instrument Accessories

• Rectangular cells 50 mm (1.14944) and/or
• Rectangular cell 100 mm (only for Prove 600 (plus)) (1.74011)

Other Reagents and Accessories

• Water for analysis, EMSURE^® (1.16754) or
• Distilled water
• Membrane filters made of cellulose nitrate, pore size 0.45 µm
• Refractometer
• Ultrasound bath
• 250-mL conical flasks
• Standard laboratory glassware (e. g. glass beakers) and pipettes

Analytical Procedure

Sample Preparation

The sample must be prepared (incl RDS measurement) according to ICUMSA^® Method GS2-10 (2024), chapter 8.²

Measurement

General instructions for performing the measurement, including zero setting and calibration sample blank preparation

• Select the method (2550, “Sugar Color’’) from the method list of the Spectroquant^® Prove.
• Tap on the entry field “RDS” and enter the RDS value in %. Confirm with <OK>.
• Perform a zero adjustment (procedure see “Zeroing the photometer”).
• Press <START> to start the measurement mode.
• Transfer the sample solution into a corresponding cell and place the cell into the cell compartment.
• Allow the instrument to perform the measurement automatically.
• Confirm measurement with <OK>. The IU value is shown in the display.
• Press <START> to start the measurement procedure for the next sample. The system does not prompt a repeat of the zero adjustment.

Zeroing the photometer

• The photometer must be zeroed before each new measurement series.
• A rectangular cell is filled with water for analysis for use in the zero adjustment.
• It is advisable to zero the photometer using the same cell as the one used for the measurement sample or else a cell with identical optical characteristics and an identical absorption (matched pair).
• The zero-adjustment procedure for the measurement series is automatically prompted by the instrument after the entry of the weight of the first analytical sample.

Evaluation

Results are expressed in ICUMSA^® units (IU).