Melanoidins from coffee infusions. Fractionation, chemical characterization, and effect of the degree of roast.

A method involving fractionation in ethanol aqueous solutions, anion exchange chromatography, and immobilized copper chelating chromatography was developed to obtain high molecular weight anionic melanoidin populations from coffee infusions. Six anionic fractions with different physicochemical properties (ethanol solubility and chelating ability) and chemical composition regarding carbohydrate as well as protein nature and content were isolated. Fractions with similar chemical composition were obtained for light-, medium-, and dark-roasted coffee infusions. These melanoidin fractions accounted for 30-33% of the cold-water soluble high molecular weight material, independently of the degree of roast in coffee. The nature and abundance of the different polysaccharides in each fraction were dependent on their ethanol solubility. The 50% ethanol insoluble melanoidin populations contained mostly galactomannan-like carbohydrates, and the fractions obtained with 75% ethanol contained mostly arabinogalactan-like carbohydrates. The melanoidin populations with chelating properties presented significantly lower carbohydrate content and, from these, the 75% ethanol soluble fractions were almost devoid of carbohydrate material. The results obtained suggest that the chelating ability of these coffee melanoidins is modulated by their carbohydrates.