title: Thermal stability of spent coffee ground polysaccharides: galactomannans and arabinogalactans.
abstract: In order to better understand the thermal stability of spent coffee grounds (SCG) galactomannans and arabinogalactans and the reactions that can occur upon roasting, long term isothermal exposures, up to 3h, were performed at 160, 180, 200, 220, and 240 °C. The resultant products were analysed according to the sugars and linkage composition and also by electrospray mass spectrometry. Galactomannans did not loss mass at T ≤ 200 °C during exposures up to 3h whereas the arabinogalactans showed that thermal stability only for T ≤ 180 °C. This was in accordance with the estimated activation energies of their thermal decomposition of 138 kJ/mol and 94 kJ/mol, respectively. The roasting of galactomannans promoted the formation of new glycosidic linkages, with occurrence of 2-, 6-, 2,3-, 2,6-, 3,6-, 2,3,6-, 3,4,6-linked mannose residues, 3,4,6-linked galactose residues, and terminally-linked glucose residues, observed by methylation analysis. Depolymerisation and formation of anhydrohexose residues at the reducing end and mannose-glucose isomerisation were also observed. The roasting of galactomannans at 200 °C promoted their solubility in water upon alkali extraction and neutralisation.
authors.affiliation: Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Joana
authors.initials: J
authors.lastname: Simões
authors.forename: Elia
authors.initials: E
authors.lastname: Maricato
authors.forename: Fernando M
authors.initials: FM
authors.lastname: Nunes
authors.forename: M Rosário
authors.initials: MR
authors.lastname: Domingues
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Coimbra
mesh_terms: D003069:Coffee / Q000737:chemistry*; D004355:Drug Stability; D005511:Food Handling; D005685:Galactans / Q000737:chemistry*; D005690:Galactose / Q000031:analogs & derivatives; D008351:Mannans / Q000737:chemistry*; D012995:Solubility; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D003069:Coffee; D005685:Galactans; D008351:Mannans; D014867:Water; C012990:galactomannan; C005653:arabinogalactan; D005690:Galactose
keywords: Activation energy of thermal decomposition; Coffee residue; Mass spectrometry; Roasting; Thermogravimetry