Melanins

In the presence of enzymatic complexes, as PPO - polyphenol oxidase, in an oxidant environment, polyphenols are oxidized, forming quinones. These compounds may react with o-diphenols, amino acids, proteins (Mersad et al., 2000) or other quinones, forming polymeric compounds.
The formation of enzymatic browning compounds in juices depends on the cane variety, on type and concentration of phenolic compounds, and on the activity of enzymes involved in the oxidation reaction (Paton, 1992). Some products of this reaction present an intense dark brown colour, as in the melanines.  

Bibliography

Mersad A., R. Lewanndowski, M. Decloux, 2000, Colorants in cane sugar industry, Proc. of S.I.T. Conf., 235-
          247
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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