The hydrophobic polysaccharides of apple pomace

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.