Blueberry cell wall fractionation and intermolecular binding between pectin rich fractions and anthocyanins
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Blueberry cell wall fractions extracted with increasingly strong solvents were subjected to GC-MS for neutral sugar profile and glycome profiling. Water soluble (WSF), chelator soluble (CSF) and sodium carbonate soluble (NSF) fractions were pectin rich fractions with 50-60% uronic acid content. Pectin rich fractions had xyloglucan, HG backbone and arabinogalactans epitopes, and arabinose and galactose were the two major neutral sugars. WSF and CSF had high Mw of 450 kDa in the major eluting peak, while NSF had smaller Mw of 170 kDa. Pectin rich fractions were incubated with anthocyanin solutions under pH 2-4.5, and bound and free anthocyanin were separated by centrifugal ultrafiltration. WSF, CSF and NSF all reduced free anthocyanin pigment concentration in the filtrates, and the binding was more significant at pH 2 and pH 3.6. Ionic interaction between pectic free carboxyl groups and anthocyanin flavylium cation and anthocyanin aromatic stacking were concluded as the major binding mechanisms.