title: Transglycosylation reactions between galactomannans and arabinogalactans during dry thermal treatment.
abstract: Aiming to investigate the possible occurrence of transglycosylation reactions between galactomannans and side chains of arabinogalactans during coffee roasting, mixtures of β-(1 → 4)-D-mannotriose and α-(1 → 5)-L-arabinotriose were subjected to dry thermal treatments at 200 °C. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis allowed identifying polysaccharides composed by pentose and hexose residues with a degree of polymerization up to 18 residues. Methylation analysis showed the occurrence of new types of glycosidic linkages in all thermally treated mixtures, as well as the occurrence of terminally and 5-linked ribose, possibly formed from arabinose isomerization. Also, xylose and lyxose were identified and proposed to be formed from mannose. These results support the occurrence of transglycosylation reactions promoted by roasting involving both oligosaccharides in the starting mixtures, resulting in arabinan and mannan chimeric polysaccharides. These structural features were also found in roasted coffee polysaccharide samples.
authors.affiliation: QOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Ana S P
authors.initials: AS
authors.lastname: Moreira
authors.affiliation: QOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Joana
authors.initials: J
authors.lastname: Simões
authors.affiliation: QOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Andreia T
authors.initials: AT
authors.lastname: Pereira
authors.affiliation: QOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Cláudia P
authors.initials: CP
authors.lastname: Passos
authors.affiliation: CQ-VR, Chemistry Research Centre, Department of Chemistry, University of Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal.
authors.forename: Fernando M
authors.initials: FM
authors.lastname: Nunes
authors.affiliation: QOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: M Rosário M
authors.initials: MR
authors.lastname: Domingues
authors.affiliation: QOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: mac@ua.pt.
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Coimbra
mesh_terms: D002236:Carbohydrate Conformation; D003069:Coffee / Q000737:chemistry*; D005511:Food Handling / Q000379:methods; D005685:Galactans / Q000737:chemistry*; D005690:Galactose / Q000031:analogs & derivatives; D006031:Glycosylation; D006358:Hot Temperature; D006868:Hydrolysis; D008351:Mannans / Q000737:chemistry*; D009844:Oligosaccharides / Q000737:chemistry; D010084:Oxidation-Reduction; D010429:Pentoses / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014312:Trisaccharides / Q000737:chemistry*
chemical_list: D003069:Coffee; D005685:Galactans; D008351:Mannans; D009844:Oligosaccharides; D010429:Pentoses; D014312:Trisaccharides; C012990:galactomannan; C043333:lyxose; C023872:mannotriose; C005653:arabinogalactan; D005690:Galactose
keywords: Coffee; Dry heating; MALDI-MS; Polysaccharides; Roasting; Transglycosylation