Colourants distribution in the crystal and in the syrup layer is important to understand colour distribution during refining. Raw sugar is considered to have good refing quality when, after affination, the percentage of colourants in the affined crystal is low.
The knowledge of the type of colourants that remains inside the crystal is important in order to evaluate their behavior during refining. Paton, 1992, using molecular exclusion chromatography, observed that the majority of compounds inside crystals have with high molecular weight. She calculated that 70% of a raw sugar colour, recently crystallized, without storage, is originated by high molecular weight compounds (measured at 405 nm).
Phenolic compounds of flavonoid type also contribute to raw sugar colour. Concentration of these compounds in Australian raws vary between 10 ppm and 60 ppm, contributing untill 30% of sugar colour, at pH 7 (Smith and Paton, 1985).
Bento et al. (1997) using GPC - Gel Permeation Chromatography and a ELS - Evaporative Light Scattering detector demonstrated that clourants with high molecular weight in raw sugar have tendency to remain in sugar crystal after affination.
Bento L.S.M., Pereira M.E., Sa S., 1997, Gel permeation chromatography of sugar
materials using spectrphotometric and evaporation light scattering detectors,
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Paton N.H., 1992, The origin of colour in raw sugar, Proc. of Aust. S.S.C.T. Conf., 8-17
Smith P., Paton N.H., 1985, Sugar cane flavonoids, Sugar Tech. Rev., 12. 117-142