title: Microwave superheated water and dilute alkali extraction of brewers' spent grain arabinoxylans and arabinoxylo-oligosaccharides.
abstract: Microwave superheated water extractions (MWE) were performed to evaluate the feasibility of this technology for quantitative recovery of the arabinoxylans (AX) or arabinoxylo-oligosaccharides (AXOS) from brewers' spent grain (BSG). The AX+AXOS yield increased with the increase of the temperature in the range from 140 to 210 °C during 2 min. The higher temperatures promoted depolymerisation, debranching, and deesterification of the polysaccharides, with formation of brown products. The conditions that promote a compromise between the yield and the structure obtained, minimizing the thermal degradation of the fractions extracted by MWE are the following: (1) 140 °C, to remove the residual starch mixed with β-glucans; (2) Suspension of the residue left in water and treated at 180 °C; (3) suspension of the residue in 0.1 M KOH and treated at 180 °C. Using this sequential procedure, it was possible to extract 62% of BSG AX+AXOS, presenting degrees of polymerization ranging between 7 and 24 xylose residues, and a degree of phenolic acids esterification between 5 and 21%. The structural variability obtained by MWE allows defining specific types of compounds for different applications and uses depending on the extraction conditions used.
authors.affiliation: QOPNA, Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal. Electronic address: ecoelho@ua.pt.
authors.forename: Elisabete
authors.initials: E
authors.lastname: Coelho
authors.forename: M Angélica M
authors.initials: MA
authors.lastname: Rocha
authors.forename: Jorge A
authors.initials: JA
authors.lastname: Saraiva
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Coimbra
mesh_terms: D002523:Edible Grain / Q000737:chemistry; D001467:Hordeum / Q000737:chemistry; D006878:Hydroxides / Q000737:chemistry; D059625:Liquid-Liquid Extraction / Q000379:methods; D008872:Microwaves; D009844:Oligosaccharides / Q000737:chemistry / Q000302:isolation & purification*; D017680:Potassium Compounds / Q000737:chemistry; D013696:Temperature; D014867:Water / Q000737:chemistry; D014990:Xylans / Q000737:chemistry / Q000302:isolation & purification*; D014994:Xylose / Q000737:chemistry / Q000302:isolation & purification*; D047071:beta-Glucans / Q000737:chemistry / Q000302:isolation & purification*
chemical_list: D006878:Hydroxides; D009844:Oligosaccharides; D017680:Potassium Compounds; D014990:Xylans; D047071:beta-Glucans; D014867:Water; C085118:arabinoxylan; D014994:Xylose; C029943:potassium hydroxide
keywords: Arabinoxylans; Barley; Brewer's spent grain; Feruloylated arabinoxylo-oligosaccharides; Food ingredients; Microwave-assisted extraction; Polysaccharides; Prebiotics