Arabinosyl and glucosyl residues as structural features of acetylated galactomannans from green and roasted coffee infusions.
A good yield mild fractionation procedure was developed for the purification of mannans from green and roasted coffee infusions that included anion-exchange chromatography and phenylboronic acid immobilized Sepharose chromatography of the dialyzed and ethanol precipitated material. Enzymatic hydrolysis with endo-beta-mannanase and ESIMS allowed finding that the mannans from roasted coffee infusions, as well as those from green coffee, are acetylated (8 mol% and 11 mol%, respectively). Fragmentation pattern obtained by ESIMS/MS analysis of the acetylated oligosaccharide ions indicates that the acetylation also occurs at O-2 of the mannose residues. Doubly acetylated and contiguously acetylated hexose residues were also found. Arabinose residues, as side chains, were also found as structural features of hot water soluble green (2%) and roasted (<0.9 mol) coffee galactomannans. Methylation analysis, hydrolysis with specific glycosidases and GC-EIMS analysis of the reduced and methylated oligosaccharides allowed to conclude that beta-(1-->4)-linked glucose residues are also structural features of green and roasted coffee galactomannans (6 and 1 mol%, respectively). In hot water soluble green coffee mannans, glucose residues are a constituent of the mannan backbone, and in the roasted coffee they were detected only at the reducing end of the mannan backbone.
Nunes
Fernando M
FM
Departamento de Química, Universidade de Trás-os-Montes e Alto Douro, P-5000-911 Vila Real, Portugal. fnunes@utad.pt
Domingues
M Rosário
MR
Coimbra
Manuel A
MA
D000107:Acetylation; D001089:Arabinose / Q000737:chemistry*; D002240:Carbohydrate Sequence; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003069:Coffee / Q000737:chemistry*; D005690:Galactose / Q000031:analogs & derivatives; D005947:Glucose / Q000737:chemistry*; D006027:Glycosides / Q000737:chemistry; D006868:Hydrolysis; D008351:Mannans / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D010429:Pentoses / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D013662:Tea / Q000737:chemistry*
D003069:Coffee; D006027:Glycosides; D008351:Mannans; D010429:Pentoses; D013662:Tea; C012990:galactomannan; D001089:Arabinose; D005947:Glucose; D005690:Galactose