COLORANT REMOVAL DURING CLARIFICATION AND DECOLORISATION PROCESSES

FOR PRODUCERS of raw sugar, current global conditions of oversupply and poor economic returns are placing increasing emphasis on quality in order to maintain access to premium markets. The key parameter in the eyes of most refiners of raw sugar is colour. Consequently, much past research has concentrated on attempts to better quantify the chemical nature of raw sugar colorants, assess their behaviour during various processing stages, and understand their deleterious effects upon sugar quality. High molecular weight (HMW) colorants have long been implicated in raw sugar refinability issues. This paper describes detailed studies of colour removal in three refineries that were conducted to formulate a more complete understanding of HMW colorants, as well as allow the comparison of colorants across a range of sugars and refining processes. Colour, phenolics, very high molecular weight (VHMW) and HMW colorants were monitored through three refineries that use different combinations of clarification and decolorising techniques, allowing the efficiency of removal of each particular colorant to be evaluated at different stages through the different refineries. Sampling of refinery streams was performed at varying times to attempt to capture differences in the incoming raw sugars, as well as the service life of particular decolorising systems, in order to gain a representative picture. The prior identification of some specific HMW colorants as being difficult to remove in refineries has now sharpened the focus on developing techniques to better understand and quantify HMW colorants. Factory control measures aimed at minimising their production should therefore produce better refining raw sugars, while processes that are known to produce particular colorants implicated in poor refinability could be more carefully monitored and maintained. The ultimate goal would be to apply such knowledge from refinery studies in order to produce higher quality, better refining raw sugars.