title: Evaluation of the effect of roasting on the structure of coffee galactomannans using model oligosaccharides.
abstract: The roasting process induces structural changes in coffee galactomannans. To know more about the reaction pathways that occur during the roasting of coffee, mannosyl and galactomannosyl oligosaccharides, having a degree of polymerization (DP) between 3 and 4, were used as models for galactomannans. These compounds were dry-heated under air atmosphere from room temperature to 200 °C, being maintained at 200 °C for different periods of time. The roasted materials were analyzed by mass spectrometry (ESI-MS, MALDI-MS, and ESI-MSn) and methylation analysis. In the MS spectra were identified several [M+Na]+ ions belonging to a series from a single hexose to 10 hexose residues ([Hex1-10+Na]+). The ions corresponding to their respective mono- and tridehydrated derivatives ([Hex2-10-H2O+Na]+ and [Hex2-10-3H2O+Na]+, respectively) were also identified. ESI-MSn as well as deuterium-labeling and alditol derivatization experiments showed that the tridehydrations occur at the reducing end of the oligosaccharides. The identification of (1→2)- and (1→6)-linked mannose residues and (1→4)-linked glucose residues by methylation analysis allowed the conclusion that transglycosylation and isomerization reactions occur during dry thermal processing.
authors.affiliation: QOPNA, Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Ana S P
authors.initials: AS
authors.lastname: Moreira
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Coimbra
authors.forename: Fernando M
authors.initials: FM
authors.lastname: Nunes
authors.forename: Joana
authors.initials: J
authors.lastname: Simões
authors.forename: M Rosário M
authors.initials: MR
authors.lastname: Domingues
mesh_terms: D040503:Coffea / Q000737:chemistry*; D004355:Drug Stability; D005690:Galactose / Q000031:analogs & derivatives; D006358:Hot Temperature; D008351:Mannans / Q000737:chemistry*; D013058:Mass Spectrometry; D009844:Oligosaccharides / Q000737:chemistry*; D012639:Seeds / Q000737:chemistry*
chemical_list: D008351:Mannans; D009844:Oligosaccharides; C012990:galactomannan; D005690:Galactose