Abstract
The potential of poly- and oligosaccharides as functional ingredients depends on the type and glycosidic linkages of their monosaccharide residues, which determine their techno-functional properties, their digestibility and their fermentability. To isolate the pectic polysaccharides of cranberry, alcohol insoluble solids were first obtained from pomace. A sequential extraction with hot phosphate buffer, chelating agents (CH), diluted (DA) and concentrated sodium hydroxide was then carried out. Pectic polysaccharides present in CH and DA extracts were purified by anion exchange and gel filtration chromatography, then sequentially exposed to commercially available pectin-degrading enzymes (endo-polygalacturonase, pectin lyase and endo-arabinanase/endo-galactanase/both). The composition and linkages of the generated fragments revealed important characteristic features, including the presence of homogalacturonan with varied methyl esterification extent, branched type I arabinogalactan and pectic galactan. The presence of arabinan with galactose branches was suggested upon the analysis of the fragments by LC-MS.
Highlights
Among plant cell wall polysaccharides, the pectic polysaccharides (PPS) are characterized by high versatility and complexity of their structure, composed of smooth and hairy regions [1,2]
The smooth region consists mainly of homogalacturonan, with smaller amounts of xylogalacturonan; homogalacturonan is a linear polymer of α-(1,4)-D-galacturonic acid [3], which can be partially methyl esterified at the carboxylic group of C6 and acetylated at C2 and C3
The present study provides a first characterization of some of the PPS obtained from cranberry pomace by chelating agents (CH) and diluted alkaline (DA) extractions [23]
Summary
Among plant cell wall polysaccharides, the pectic polysaccharides (PPS) are characterized by high versatility and complexity of their structure, composed of smooth and hairy regions [1,2]. The galacturonic acid residues are partially acetylated as in homogalacturonan, while the rhamnose residues can be branched at C3 or C4 with oligomers of arabinose and galactose These neutral branches show great variability between different species, tissues and even in the same tissue in function of physiological changes such as ripening [6,7], but commonly include oligomers of α-(1,5)-Larabinofuranose (arabinan), of β-(1→4)-D-galactopyranose (galactan), or mixed (arabinogalactans type I and II, which possess a backbone of galactan and arabinose-containing branches). Smooth and hairy regions are found in variable proportions in extracted plant cell PPS and can be separated from each other only by enzymatic activity or strong chemical treatments This indicates that they are covalently bound to each other, likely by the galacturonic acid extremities of their backbones [4,5]. Cranberry pomace, obtained during the juice manufacturing process, is a very abundant residual material This material contains large amounts of cell wall polysaccharides, including PPS. The contribution of our findings for the elucidation of the structural properties of RG I in cranberry cell walls was discussed
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