Sequential microwave superheated water extraction of mannans from spent coffee grounds


The feasibility of using sequential microwave superheated water extraction (MAE) for the recovery of mannans from spent coffee grounds (SCG) was studied. Due to the high contents of mannose still present in the SCG residue left after two consecutive MAE, the unextracted material was re-suspended in water and submitted to a third microwave irradiation (MAE3) at 200 degrees C for 3 min. With MAE3, mannose recovery achieved 48%, increasing to 56% by MAE4, and reaching a maximum of 69% with MAE5. Glycosidic-linkage analysis showed that in MAE3 mainly galactomannans were recovered, while debranched galactomannans were recovered with MAE4 and MAE5. With increasing the number of extractions, the average degree of polymerization of the mannans decreased, as observed by size-exclusion chromatography and by methylation analysis. Scanning electron microscopy images showed a decrease on cell walls thickness. After final MAE5, the remaining un-extracted insoluble material, representing 22% of the initial SCG, was composed mainly by cellulose (84%). (C) 2013 Elsevier Ltd. All rights reserved.



subject category

Chemistry; Polymer Science


Passos, CP; Moreira, ASP; Domingues, MRM; Evtuguin, DV; Coimbra, MA

our authors


Thanks are due to Fundacao para a Ciencia e a Tecnologia (FCT, Portugal), European Union, QREN, FEDER and COMPETE for funding the QOPNA research unit (project PEst-C/QUI/UI0062/2013; FCOMP-01-0124-FEDER-037296). Claudia Passos was supported by a post-doc grant by FCT (SFRH/BDP/65718/2009). Thanks are also due to Dr. Diana Pinto and Prof. Artur Silva from the Department of Chemistry of the University of Aveiro for the assessment to the microwave facilities and assistance.

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