Colourants - Milling

By Bento, Luis San Miguel
Posted on 2007-08-29    Last edited on 2009-09-10

After milling, mixed juice contains the majority of sucrose in cane. Are also extracted polysaccharides originates from cane or formed after harvesting, cane pigments including flavonoids and other phenolic compounds. Durante a moenda há uma diminuição da concentração dos ácidos clorogénicos, dos fenóis neutros e dos flavonoides (Table 5).

Tabela 5 – Concentration of phenolic compounds in juices (Paton, 1992)

Cane juice

Mixed juice


Chlorogenic acids *



- 62%

Neutral phenolics



- 64%





* Chlorogenic acid and isomers

The decrease of phenolic compounds, from cane juice to mixed juice, can be explained by its enzymatic oxidation occurred during extraction. In the presence of PPO-polyphnol oxidase enzyme, phenols can be oxidized to quinones that can be polymerized into high molecular weight and high colour compounds.

Paton, 1992, observed by exclusion chromatography that 70% of coloured compounds, at pH 7, in first extraction juice, have molecular weight higher than the one of flavonoids. This can be explained by the formation of polymeric compounds.

Goodacre and Coombs, 1978, concluded that more than half of colour in cane juices is provoked to enzymatic browning mechanisms. According to Paton, 1992, this reaction contributes to 84% of first extraction juice colour, at pH 4. This value decreases to 53% at pH 7, due to low the IV of polymerized compounds, in relation to other phenolic compounds..

During milling sucrose concentration in juice (on solids) decreases from the first to the last mill. The relation colour/sucrose and flavonoids concentration increase through the (Paton, 1992). These compounds increase from 50ppm-150ppm, on solids, to values until 2000ppm in the last mill (Smith and Paton, 1985). In Brasil, in factories producing alcohol from juice, the juice of last mills is used for alcohol production, and those from first mills is used to produce sugar. Doing this way, sugar colour decreases significantly, to values of 80IU, comparing with cvalues of 150IU when all the juice is used to produce sugar.

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