Chemical characterization of galactomannans and arabinogalactans from two arabica coffee infusions as affected by the degree of roast.

Galactomannans and arabinogalactans compose almost exclusively the polysaccharide fraction of roasted coffee infusions. To increase the knowledge about the effect of the degree of roast (DR) in the amount and chemical structure of the galactomannans and arabinogalactans, two arabica coffees of different geographical origins (Costa Rica and Brazil) were roasted for three degrees of roast (DRs 4.7-5.0, 8.7, and 10% of dry weight loss of green coffee beans, on a dry basis). The high molecular weight material was extracted with hot water and dialyzed (molecular weight cutoff >12 kDa), and the material was separated in three cold-water-soluble fractions by graded addition of ethanol. The degree of polymerization and the degree of branching of the galactomannans decreased with the increase of the DR. As the DR increased, less branched arabinogalactans were extracted. The relative amount of terminally linked arabinosyl residues of the arabinogalactans decreased with the increase in DR, and the terminally linked galactosyl residues increased. Also, the size of the arabinosyl side chains of the arabinogalactans decreased with the increase in DR.