Extraction and characterization of polysaccharides from green and roasted Coffea arabica beans

Abstract

Polysaccharides were sequentially extracted from green and roasted Coffea arabica beans with water (90 °C), EDTA, 0.05, 1, and 4 M NaOH and characterized chemically. Additionally, the beans were subjected to a single extraction with water at 170 °C. Green arabica coffee beans contained large proportions of 1→4-linked mannans, of which on average 1 in every 23 mannopyranose residues was branched with single unit galactose side-chains at O-6. A part of these galactomannans could be extracted relatively easy with water and EDTA. These galactomannans were found to have a relatively high degree of branching (gal:man∼1:8) and a relatively low molecular weight in comparison to the remaining galactomannans (gal:man∼1:15–24). Additionally, 1→3-linked galactans, heavily branched at O-6 with side-chains containing arabinose and galactose residues, were present in the green coffee beans, as well as smaller amounts of pectins, cellulose, and xyloglucans. Roasting resulted in a loss of 8% of the dry weight. This could be partly explained by the relatively high percentage of sugars which was lost during the roasting process, most probably as a result of conversion into, e.g. Maillard and pyrolysis products. After roasting the extractability of polysaccharides was increased significantly. A decrease in the degree of branching as well as a decrease in molecular weight of arabinogalactans, galactomannans, and xyloglucans was observed after roasting.