Syrup Color removal
Decolourisation is necessary to reduce the refined sugar colour to meet the EEC2 white sugar specification standards.
Pure sucrose is colourless, but may appear coloured because of the inclusion of small amounts of coloured material in the sugar.
Colour is the generic term used to cover a wide range of components which contribute to the colour of sugar.
Most of these compounds are complex and not easy to quantify and colour is measured as the total effect of all colorants on light absorbance at 420 nm.
This is not altogether satisfactory, because different colorant components behave differently in the various processing and decolourizing operations.
The refining process incorporates colour removal steps.
Raw sugar solutions, made by extracting sugar beet pulp, and, to an ever greater extent, the juice extracted from sugar cane, are naturally yellow-brown / brown. This coloration increases during processing as a result of the enzyme-catalyzed and heat- induced procedures involved. These include the Maillard reaction between sugar and amino acids, enzymatic browning and caramelization. Colored products are also produced through the alkaline decomposition of sugars.
Decolorization units are typically used in the corn sweetener process just before deashing units. Their main purpose is to remove syrup stream components which contribute to color and off-flavors.
Decolorization with ion exchange resins complements traditional purification methods, the most important of which is crystallization.
Ion exchange resins used in the sugar industry as decolorizers are of the strong-base anionic type, with quaternary amine functional groups. They are operated in the chloride form.
A multi-stage process is applied to produce white granulated sugar or clear sugar solutions from sugar cane or sugar beet.
Decolorization with ion exchange resins is a standard procedure. Many types of compounds contribute to the color of sugar solutions, but most colorants are polar compounds that are adsorbed well by low crosslinked anion exchange resins.
In an ION-IX system, the ION-IX valve continuously distributes the feed, wash, regeneration, and rinse streams through the stationary resin columns so that all resin is in active duty. The process “moves” in a circle, moving through each operation, one step at a time from one column to the next. The rotational speed is proportional to the colour removal load required.
Example of a cane syrup decolorizing unit using the ION-IX technology
ICUMSA : International Commission for Uniform Methods of Sugar Analysis
A sugar juice free of suspended solids, corrected to pH 7, and of known solids concentration is analysed using a spectrophotometer set to 420nm.
The color is calculated as follows:
ICUMSA 420 Color = As x 10.000 / bc
The absorbance, As , is divided by the product of the dissolved concentration, c (g/ml), and the cell width, b (mm).
ICUMSA 420 color is a measurement to give an indication of the overall color of the juice. This is useful in evaluating the color removal performance of a process. Clearly, no information is given about the specific types of colorants present in the sample.