The hydrophobic polysaccharides of apple pomace

abstract

In this work, polysaccharides extracted with hot water from apple pomace were isolated by C18 cartridge solid-phase extraction at pH 7 (Fr7). Dialysis (12-14 kDa) of this fraction allowed to obtain 17% (w/w) of polymeric material composed by 65% of polysaccharides, mainly arabinose (58 mol%), galacturonic acid (16 mol%) and glucose (10 mol%). Folin-Ciocalteu assay showed 62 g of phloridzin equiv/kg of polyphenols. Moreover, adjusting to pH 3, it was possible to retain an additional fraction (Fr3) representing a further 4% of the polymeric material. Fr3 contained 53% of polysaccharides composed mainly by galacturonic acid (66 mol%) and polyphenols accounted for 37 g of phloridzin equiv/kg. Precipitation with ethanol and subsequent methylation and NMR spectroscopic analysis of Fr7 dialysate allowed the identification of covalently-linked pectic-polyphenol-xyloglucan and arabinan-polyphenol complexes. These structures are possibly formed as a result of polyphenol oxidation reactions during the industrial processing of apples, conferring hydrophobic characteristics to apple pomace polysaccharides.

keywords

RICH PECTIC POLYSACCHARIDES; CELL-WALLS; STRUCTURAL CHARACTERIZATION; PHENOLIC-COMPOUNDS; HAIRY REGIONS; ARABINAN; POLYPHENOLS; JUICE; NMR; OLIGOSACCHARIDES

subject category

Chemistry; Polymer Science

authors

Fernandes, PAR; Silva, AMS; Evtuguin, DV; Nunes, FM; Wessel, DF; Cardoso, SM; Coimbra, MA

our authors

acknowledgements

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) and to CITAB research Unit (FCT UID/AGR/04033/2019) through national funds and, where applicable, co-financed by the FEDER, within the PT2020 Partnership Agreement, and to the Portuguese NMR Network. This work was developed also within the scope of the project CICECO-Aveiro Institute of Materials (FCT UID/CTM/50011/2019), financed by national funds through the FCT/MCTES. Pedro A. R. Fernandes (SFRH/BD/107731/2015) were supported by FCT/MEC grants. Susana M. Cardoso thanks the research contract under the project AgroForWealth: Biorefining of agricultural and forest by-products and wastes: integrated strategic for valorisation of resources towards society wealth and sustainability (CENTRO-01-0145-FEDER-000001), funded by Centro2020, through FEDER and PT2020.

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