Colourants - Affination

In Affination the majority of colourants in raw sugar are separated to the affined syrup. A decolourization of circa 62%, in relation to raw sugar colour, is achieved in this operation (Godshall et al., 1987).

High molecular compounds in the raw sugar will be preferentially retained in the affined sugar. This was confirmed by GPC technique with an ELS detector (Bento et al., 1997). The percentage of compounds with molecular weight over 250kD, Group A, increased from the raw sugar (2,8%) to the respective affined sugar (9,2%) (on total high molecular compounds) (Table 1). Included in these compounds are polysaccharides which represent 70% from total very high molecular compounds in raw sugar (Godshall et al., 1987).
Compounds with molecular weight between 12kD and 50kD (Group B) changed from 56% in raw sugar to 70% in affined sugar.
Compounds of molecular weight between 2,5kD and 12kD (Group C) decreased about 50% during affination.

Table 1 - High molecular weight compounds in refinning

Figure 1 - ELS diagram from Affination, Carbonatation and Fine liquor

With ELS technique it is not possible to study low MW compounds as sucrose interfere with the results. However we can compare the chromatograms at 330nm of raw sugar and affined sugar solutions (Bento, 2008). In Table 2 the valuesof colour at 330nm of raw sugar and affined sugar are compared. In this Table it was observed that the colour at 330 nm due to low molecula weight compounds increase from 22% on total colour of raw sugar to 38% on total colour of affined sugar (Bento, 2008). This low MW compounds are mainly phenols and their degradation products, with high IV. This explains increase of IV through Affination, from 3.0 IV to 3.6 IV, as referred by Kennedy and P. Smith, 1976.

Table 2 - Distribution of colour at 330nm

Figure 2 - Colour at 330nm of RawSugar, Affined Sugar and Affination syrup

Paton, 1992, in experiments using high speed centrifugation, with a separation of syrup in a quantity of 2% on raw sugar, observed that the majority of cinnamic acids, chlorogenic acid and flavonoids, are separated to the syrup. Regardind the neutral phenolics, only 30% are separated to the syrup. This shows that these compounds are preferentially inside of the raw sugar crystals.

Bibliography

Bento L.S.M., M.E. Pereira, S. Sa, 1997, Gel permeation chromatography of sugar materials
using spectrophotometric and evaporator light scattering detector, Proc.of S.I.T. Conf., 383-392
Bento L.S.M., 2008, Colourants throgh cane sugar production and refining, S.P.R.I. meeting (in press)Godshall M.A., M.A. Clarke, C.D. Doodley, E.J. Roberts, 1987, Large colorants and polysaccharide
molecules in raw cane sugars, Proc. of S.I.T. Conf., 193-211
Kennedy A.M. and P. Smith, 1976, Color in Refineries, Proc. S.I.T. Conf., 35 : 156-160
Paton N.H., 1992, The origin of colour in raw sugar, Proc. of Aust. S.S.C.T. Conf., 8-17

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