CHEMICAL STRUCTURES OF GREEN COFFEE BEAN POLYSACCHARIDES

The chemical structures of green coffee bean polysaccharides have been determined by methylation analysis of whole beans and of extracted polymer-rich fractions. Ground beans were completely solubilized in 4-methyImorphoIine N-oxide, and the Hakomori methylation procedure was applied directly. The polysaccharide fraction in Robusta beans constitutes 48% of the dry weight and is principally composed of three polymers: arabinogalactan, mannan, cellulose. The arabinogalactan has a β1→3-linked galactan main chain with frequent arabinose and galactose residue containing side chains, whereas the mannan resembles cellulose in that it has a linear β1→4-linked structure. Only occasional single-residue galactose side chains are present in the mannan fraction. Polysaccharide compositions of Robusta and Arabica beans are similar; the only significant difference is the higher content (approximately 3%) of arabinogalactan in the former type. © 1990, American Chemical Society. All rights reserved.