Polysaccharides of green Arabica and Robusta coffee beans

Two independent procedures for the quantitative determination of the polysa ccharide content of Arabica Caturra (Coffea at arabica var. Caturra) and Ro busta ROM (Coffea canephora var. ROM) green coffee beans showed that they b oth contained identical amounts of polysaccharide. Cell wall material (CWM) was prepared from the beans and partial solubilisation of component polysa ccharides was effected by sequential extraction with water, 1 M KOH, 0.3% N aClO2, 4 M KOH and 8 M KOH. The monosaccharide compositions of the CWMs wer e similar, although Arabica beans contained slightly more mannose than Robu sta. In the latter, more arabinogalactan was solubilised during preparation of the CWM and the water-soluble fraction of the CWM contained higher amou nts of galactomannan than in Arabica. Linkage analysis indicated that the g alactomannans possessed unbranched to branched mannose ratios between 14:1 and 30:1 which is higher than previously reported. No major difference in t he structural features of the galactomannans between species was found. The arabinogalactans were heterogeneous both with regard to the degree of bran ching and the degree of polymerisation of their arabinan side-chains. Compa red to Arabica, Robusta appeared to contain greater amounts of arabinogalac tans with longer side chains. It is concluded that there was no detectable difference between the Arabica and Robusta varieties of this study in their absolute polysaccharide content or in the gross structural features of the ir galactomannans. Differences were apparent both in the structural feature s and case of solubility of the arabinogalactans but a more detailed study of several varieties of Arabica and Robusta will be required to determine w hether these differences occur consistently between species. (C) 2001 Elsev ier Science Ltd. All rights reserved.