Optimization of process parameters for decolorization of melanoidins using powdered activated carbon and determination of their molecular weight by Gel Permeation Chromatography

In this study, the aqueous melanoidin solution (as a model for the colorant present during thick beet juice processing) were decolorizied by powdered activated carbon. A Response Surface Methodology (RSM) was applied to optimize the operating variables of the decolorization process. The results revealed that the optimal values of the process parameters for concentration of melanoidins equal to 750.0 mgL-1 were as follow: pH of 7 and reaction time of 30 min. Under these optimal conditions, the color removal performance was achieved 73.07% and 93.0% for aqueous melanoidin solution and sugar beet syrup, respectively with the addition of 0.1 g of powdered activated carbon. Chemical specifications of synthetic melanoidins and activated carbon, before and after adsorption process were determined using Fourier transform infrared. Decolorization kinetic parameters indicated that the adsorption of melanoidins was followed from pseudo-first order equation. Furthermore, adsorption isotherm studies indicated that melanoidins adsorption was correlated reasonably well by Langmuir isotherm model. In following, molecular size distribution of melanoidins was studied in order to get a better understanding of the evolution distribution molecular weight of melanoidins during decolorization processes. Analysis confirmed the presence of melanoidins with molecular weight distribution between 0.7 kDa to 4000.0 kDa. The colorants with a molecular mass of 4000.0 kDa were completely removed whereas components above 230.0 kDa, 7.0 kDa and 0.7 kDa presented lower removal efficiencies, showing lower affinity on powdered carbon during decolorization process. The results of this study indicated that powdered activated carbon has a good potential for removal of the high molecular weight colored impurities in thick beet juice.