Structural features of spent coffee grounds water-soluble polysaccharides: Towards tailor-made microwave assisted extractions


This work studies the microwave-assisted extraction conditions for recovery of polysaccharides from spent coffee grounds, including their effect on arabinogalactans and galactomannans polymerization and branching structural features. Temperature (140, 170, and 200 degrees C) has the most significant impact on total extracted mass (eta(total) (soluble) (solids)) and sugars yield (eta(sugars)), arabinogalactans (eta(AG)) and galactomannans (eta(GM)), and polysaccharide mass ratio (eta(AG)/eta(GM)). Time (2, 5, and 10 min) and alkali (diluted 0.1 M NaOH) treatments have less influence. Alkali treatment and shorter time (2 min) provided a protective effect against polysaccharides degradation. At 170 degrees C, the yield of arabinogalactans was found to be significantly higher than that of galactomannans (eta(AG)/eta(GM) > 1). Increasing temperature to 200 degrees C leads to decrease the polymerization of polysaccharides, promoting the formation of debranched polysaccharides and oligosaccharides. This study shows that the optimum conditions for polysaccharides extraction cannot be selected only by mass yield but need to be defined according to the desired structural features for the specific applications.




Chemistry; Polymer Science


Passos, CP; Rudnitskaya, A; Neves, JMMGC; Lopes, GR; Evtuguin, DV; Coimbra, MA

nossos autores


This work was financially supported by the project PulManCar - POCI-01-0145-FEDER-029560- funded by FEDER, through COMPETE2020 - Programa Operacional Competitividade e Internacionalizacao (POCI), and by national funds (OE), through FCT/MCTES. Thanks are due to the University of Aveiro and FCT/MCT for the financial support for the QOPNA research Unit (FCT UID/QUI/00062/2019) through national founds and, where applicable, co-financed by the FEDER, within the PT2020 Partnership Agreement, and to the Portuguese NMR Network. CESAM (UID/AMB/50017 - POCI-01-0145-FEDER-007638) thanks FCT/MCTES through national funds (PIDDAC), and the co-funding by the FEDER, within the PT2020 Partnership Agreement and Compete 2020. The financial support of CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement is also greatly acknowledged. Claudia Passos (SFRH/BPD/107881/2015) and Alisa Rudnitskaya (SFRH/BPD/104265/2014) were supported by post-doc grants by FCT, while Guido Lopes (SFRH/BD/104855/2014) was supported by a doctoral grant by FCT. This work was also funded by national funds (OE), through FCT, in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. Thanks are also due to 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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