Colourants - Carbonatation

During Carbonatation there is a substancial reduction of affination liquor colour (40 - 50%). Colourants that have acidic nature can form weak bonds with calcium and will be incorporated in the calcium carbonate precipitate during growing (Davis, 2001). Kennedy and P. Smith, 1976, refer that polar polymeric colourants, with amino nitrogen and anionic at high pH, have high affinity to the calcium carbonate precipitate. Compounds of molecular weight between 12 kDa and 50 kDa, including melanoidins, are substantially removed (Figure ) (Bento and Sá, 1998).
Compounds of very high molecular weight, higher than 250 kDa, suffer a reduction of 8% (Table  Figure). Due to browning products hydrolysis, single phenols are released to carbonatation liquor. Kennedy and P. Smith, 1976, refer that carbonatation removes few cane pigments of low molecular weight. Farber, et al, 1968, refer that flavonoids are not well removed by Carbonatation, although those derived from tricine are preferentially removed (P. Smith and Paton, 1985).

  Compounds of high molecular weight in liquors

ELS diagrama of carbonated liquor (Carbonated L.) and affination liquor (Affined L.)

Due to the high alkalinity observed during Carbonatation, a hydrolysis of phenolic acids esterified to polysaccharides can occur. Due to this hydrolysis, the phenolic part, coloured,  or their oxidation products, will be separated from the carbohydrates, and therefore, its affinity to sugar crystals decreases. This fact can explain that sugars crystallized from liquors, with equivalent quality, obtained from Carbonatation and Phosphatation, are different. Sugars obtained from carbonated liquors present a lower colour than those from Phosphatation (Clarke et al., 1988). 

Bibliography

Bento L.S.M., S. Sa, 1998, Study of HMW compounds in sugar liquors from carbonatation and ion-exchange resins using GPC chromatography with an evaporative light scattering detector, Proc. of S.P.R.I. Conf., 233-247
Clarke M.A., W.S.C. Tsang, M.A. Godshall, 1988, Structure of colorants, Proc. of S.P.R.I. Conf., 183-191 
Davis S.B., 2001, The chemistry of colour removal: a processing perspective, Proc. South Afr. Sug. Tec.  Ass., 75,28-336
Farber L., E.J. Mc Donald, F. G. Carpenter, 1968, Proc. Tech. Sess. C.C.R.R., 85-101
Kennedy A.M. and P. Smith, 1976, Color in Refineries, Proc. S.I.T. Conf., 35 - 156-160
Smith P., N.H. Paton, 1985, Sugar Cane Flavonoids, Sugar Tech. Rev., 12,117-142