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Microwave superheated water and dilute alkali extraction of brewers’ spent grain arabinoxylans and arabinoxylo-oligosaccharides
- Coelho, Elisabete, Rocha, M. Angélica M., Saraiva, Jorge A., Coimbra, Manuel A.
- Carbohydrate polymers 2014 v.99 pp. 415-422
- alkali treatment, arabinoxylan, beta-glucans, depolymerization, esterification, phenolic acids, polymerization, potassium hydroxide, spent grains, starch, temperature, thermal degradation, xylose
- 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 2min. 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 0.1M 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.