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Abstract: The structure of the arabinan moiety of a purified arabinan-rich pectic polysaccharide from the cell walls of Prunus dulcis seeds was investigated by NMR spectroscopy. This polymer, which is able to induce a lymphocyte stimulatory effect, had an arabinan glycosidic-linkage composed of T-Araf: (1→5)-Araf: (1→3,5)-Araf: (1→2,3,5)-Araf in the relative proportions of approximately 3:2:1:1. Based on the 1H, 13C, COSYPR, gHSQC and gHMBC spectra of analysed arabinan, a tentative structure is presented, showing that it is composed by a very branched and, possibly, repetitive structure of seven residues. The observed (1→5) direct linkage between (1→2,3,5)-Araf and (1→3,5)-Araf residues support the occurrence of these contiguous branched residues in the arabinan backbone. [Copyright &y& Elsevier]

Pectic raw material was extracted from the alcohol insoluble residue of olive pomace. After purification, the olive pectic extract (OPE) contained 48% of galacturonic acid (GalA) and 31% of arabinose, in a total sugar content of 72%, and a degree of methylesterification (DM) of 43%. Phase diagrams were established to define the physical state of the OPE/calcium systems, at pH 3 and 7, as a function of GalA and calcium concentration. The rheological properties of the OPE/calcium systems were investigated by small-amplitude oscillatory tests. Kinetics of gel ageing and the viscoelastic properties of the cured gels were evaluated as a function of GalA and calcium concentration at pH 3 and 7. Compared with the observed behaviour of a citrus pectin, taken as representative of a commercial low-methoxyl pectin, the OPE showed higher critical GalA and calcium concentrations for gelation to occur, a larger region corresponding to homogeneous gel, and gels characterised by lower viscoelastic moduli, at similar GalA and calcium concentrations. [Copyright &y& Elsevier]

To study structure-function relationships of pectic polysaccharides with their immunostimulatory activity, broccoli by-products were used. Pectic polysaccharides composed by 64 mol% uronic acids, 18 mol% Ara, and 10 mol% Gal, obtained by hot water extraction, activated B lymphocytes in vitro (25–250 μg/mL). To disclose active structural features, combinations of ethanol and chromatographic fractionation and modification of the polysaccharides were performed. Polysaccharides insoluble in 80 % ethanol (Et80) showed higher immunostimulatory activity than the pristine mixture, which was independent of molecular weight range (12–400 kDa) and removal of terminal or short Ara side chains. Chemical sulfation did not promote B lymphocyte activation. However, the action of pectin methylesterase and endo -polygalacturonase on hot water extracted polysaccharides produced an acidic fraction with a high immunostimulatory activity. The de-esterified homogalacturonan region seem to be an important core to confer pectic polysaccharides immunostimulatory activity. Therefore, agri-food by-products are a source of pectic polysaccharide functional food ingredients. [Display omitted] • Pectic polysaccharides from broccoli by-products activate B lymphocytes. • Immunostimulation do not rely on terminal arabinose and molecular weight. • Chemical sulfation does not impact immunostimulatory activity. • De-esterified homogalacturonan regions are an important core for activity. [ABSTRACT FROM AUTHOR]

• Hydrophobic polysaccharides were isolated from apple pomace. • Pectin-polyphenol-xyloglucan and arabinan-polyphenol complexes were identified. • Polysaccharide-polyphenol complexes are formed during apple processing. • Oxidized polyphenols are covalently bonded to polysaccharides in apple pomace. • Covalently bonded polyphenols modulate polysaccharides hydrophobicity. 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. [ABSTRACT FROM AUTHOR]