Effect of roasting on the carbohydrate composition of Coffea arabica beans.
Oosterveld, A. ; Voragen, A.G.J. ; Schols, H.A. - \ 2003
Carbohydrate Polymers 54 (2003)2. - ISSN 0144-8617 - p. 183 - 192.
rich pectic polysaccharides - sugar-beet pulp - chemical characterization - hot-water - arabinose - green
Coffee beans (arabica) with different degrees of roast were sequentially extracted with water (90 °C, 1 h), water (170 °C, 30 min), and 0.05 M NaOH (0 °C, 1 h). The amount and composition of polysaccharides, oligosaccharides and monosaccharides in the extracts and residues were analyzed. The results were compared with the composition of the same batch of green arabica coffee beans. Although part of our results were already reported in rather fragmented studies, this study gives a more complete overview of the amount and composition of unextractable polymers, extractable polymers, oligomers, monomers, and their conversion into (non-sugar) degradation products as a function of their degree of roast. It was found that most carbohydrates in the roasted coffee bean were present as polysaccharides (extractable or unextractable). The fact that only a small part of the carbohydrates in the extracts were recovered as oligomer and even less as monomers, showed that oligomers and especially monomers were converted very rapidly into Maillard and pyrolysis products. Cellulose remains unextractable and its solubility was not affected by the degree of roast. Galactomannans were also mainly present as unextractable polymers in green beans, but were solubilized to a large extent with increasing degrees of roast. The arabinogalactans in the roasted bean were highly soluble at the extraction conditions used. The arabinose as present as side-chains in the arabinogalactans were found to be more susceptible to degradation at more severe roasting conditions than the galactans. Also evidence was found that populations of arabinogalactans with very different ara:gal ratios exist in the roasted beans as well as in the green beans.
Extraction and characterization of polysaccharides from green and roasted Coffea arabica beans.
Oosterveld, A. ; Harmsen, H. ; Voragen, A.G.J. ; Schols, H.A. - \ 2003
Carbohydrate Polymers 52 (2003)3. - ISSN 0144-8617 - p. 285 - 296.
rich pectic polysaccharides - sugar-beet pulp - hot-water - arabinose
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:man1:8) and a relatively low molecular weight in comparison to the remaining galactomannans (gal:man1:15–24). 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.