Decolorization of Glucose-Glycine Melanoidin as Model Color Pollutant Using Ozonation and Bacterial Treatment
Melanoidin was prepared as model color pollutant by heating equimolar amounts of glucose and glycine in sodium carbonate solution for 3 h at 121o C. After partial purification by Sephadex G-100 chromatography it was ozonated and then used as culture substrate for Bacillus subtilis. Ozone treatment for 15, 30, and 60 min resulted in decolorization (reduction in absorbance at 475 nm) values of 21.92 %, 41.10 % and 65.75 %, respectively; corresponding molecular weight (MW) values were 18.23, 15.14 and 8.66 kDa compared with a MW of 22.79 kDa for raw melanoidin. The 1-h ozonated melanoidin showed further 22.80 % decolorization after bacterial treatment for 5 days. The final MW values after combined ozonation and bacterial treatment were 16.24, 13.36, and 7.61 kDa for 15, 30, and 60 min of ozonation, respectively, followed by 5 days of bacterial treatment.
The problem of color pollution has raised much concern in alcohol distilleries and other fermentation industries utilizing sugarcane molasses as raw material. The compound mainly responsible for this color pollution is called melanoidin, which is a collective term for polymeric brown substances formed at an elevated temperature via the Maillard reaction between reducing sugars and amino acids. Many studies have already identified a number of intermediates involved in the mechanism for melanoidin production. However, little is known about the chemical characteristics of melanoidin, although some structures have been proposed for this polymeric molecule (Kato & Tsuchida 1981; Cammerer & Kroh 1995; Yaylayan & Kaminsky 1998).
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