Colour formation may hapen during raw sugar storage. In a raw sugar crystal, the syrup layer has a high brix and, therefore, is a factor for colour formation by Maillard reactions, with loss of amino nitrogen (Paton, 1992). This colour formation depends on temperature, storage time and ambient relative humidity.
Raw sugar quality is also a factor influencing colour formation. Petri and Carpenter, 1979, report that the colour of a low quality raw sugar duplicated in a storage during one year at 30ºC, but, a good quality raw sugar increased only 50%, at same conditions.
Paton, 1992, reported that a raw sugar with 3740 IU colour, stored during 20 days at 30ºC, in an atmosphere of 52% of RH, increased its colour of 42%. She observed too that cinnamic and chlorogenic acids have decreased 50%, from their initial values of 12 ppm and 23 ppm, respectively. In atmosphers of 63% of RH, more drastic changes have occurred. After 10 days of storage, raw sugar colour increased 57% and phenolic acids concentration decreased to 1ppm.
Phenolic acids concentration decreases can be explained by its oxidation (Paton, 1992). This fact is in agreament with the decrease of IV during raw sugar storage. In the examples referred above, IV decreased from 3.7 to 2.7 at 52% of RH, and to 2.1 at 63% of RH.
Neutral phenols and flavonoids, in the same example, did not suffer a great change. As these compounds are inside sugar crystals, they are not exposed to the external oxidants conditions, as the ones in the external syrup layer.
Paton N.H., 1992, The origin of colour in raw sugar, Proc. of Aust. S.S.C.T. Conf., 8-17
Petri P.H., F.G. Carpenter, 1979, Review of deterioration of raw cane sugar in
storage, Cane Sugar Refining Research Project Inc., Report No 49
Saska M., Kochergin V., 2008, Storage and production of and VLC sugars, Proc. of S.I.T
Paper # 944.