Structural features of partially acetylated coffee galactomannans presenting immunostimulatory activity

The galactomannans purified from coffee infusions have been shown to present in vitro immunostimulatory activity on murine B- and T-lymphocytes. These properties have also been shown characteristic of the galactomannans recovered from coffee residue by strong alkali solutions and rendered soluble in water by partial acetylation. In this study, purified fractions of galactomannans with immunostimulatory activity obtained from coffee infusion and from coffee residue were compared according to their average molecular weight determined by size-exclusion chromatography on Sephacryl S300, glycosidic-linkage composition by methylation analysis, selective hydrolysis by an endo-(1 → 4)-β-d-mannanase, analysis of the resultant oligosaccharide profile by Bio-Gel P2 separation, and determination of the pattern of acetylation by electrospray tandem mass spectrometry (ESI-MS/MS). It was found that the galactomannans have a comparable molecular weight (90–110 kDa), and similar glycosidic-linkage composition. However, the galactomannans from coffee residue were preferentially acetylated in the side chain residues whereas the galactomannans recovered from coffee infusions only had acetyl groups directly linked to the backbone residues. These results show that these polysaccharides that present comparable immunostimulatory properties have different acetylation patterns.