The application of reducing compounds in sugar industry is another way to reduce sugar colour. Normally, in certain countries as India, Brazil and China, sulphur dioxide is used by bubbling it through the juice, liquor or syrup. The action of SO2 promotes the reducing of colour compounds that become colourless. In this reaction double conjugated bonds, that absorb visible radiation, become saturated.
This process is used to produce white plantation sugar in sugar mill.
The utilization of sodium metabisulfite in powder added directly in vacuum pans is also used. These processes are being abandoned due to legal restrictions on residual sulfites in food products.
In cane sugar mills using alkaline sulfitation, juice is mixed with lime (7.9 L of 26 brix milk of lime per 100 L of juice) and sulfitated till 7.5 pH. Precipitate is remove with settling and decantation (Meade, Chen, 1977).
Sulphitation decolourizethose colourants with high affinity into sugar crystals (Lionnet, 1990).
Acting on mixed juice, syrup or remelt, a decolurization between 10 and 15% was obtaining with dosages of SO2 between 500 - 2500 ppm on brix (Meadows et al., 2005).SO2 is obtained burning sulfur in kilns but, for small dosages, SO2 in bottles can be used (Meadows et al., 2005).
Lionnet G.R.E., 1990, The use of sulphitation and ion exchange in the refining of cane raws, Proc. of S.Afr.
Sug. Tech. Ass., 64, 228-232
Meade, Chen (1977), Cane Sugar Handbook, 10th Edition, John Wiley & Sons, p. 149
Meadows D.M., P.M. Schorn, M. Moodley, S.D. Peackock, A. Bindoff, 2005, South African experiences with raw
sugar quality, Proc. of S.I.T. Conf., 110-120