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The effect of pectin composition on the binding selectivity to anthocyanins was investigated by Langmuir isotherms with two blueberry pectins, water soluble fraction (WSF) and chelator soluble fraction (CSF). Adsorption was four times higher between CSF and anthocyanins, than WSF and anthocyanins. Higher adsorption was attributed to the more linear, more negatively charged homogalacturonan region of CSF, compared to the more branched, neutral sugar rich WSF. The CSF binding sites ( q m a x ) to anthocyanins were estimated at 1413–1904 μg/mg pectin, which was about eight times higher than WSF binding sites. No difference was observed in binding affinity (K L) among blueberry pectins. WSF, rich in neutral sugar side chains, showed lower and more variable interaction with anthocyanins. Binding studies also showed that blueberry pectin-anthocyanins adsorption was highest at pH 3.0 and lowest at pH 4.0. Increasing concentration from 25 to 200 mM citrate-phosphate (CP) weakened the pectin-anthocyanins interaction between pH values 3.0 and 4.0. However, no significant difference in binding was observed at pH 2.6 with increasing CP. As pH values changed from 4.0 to more acidic pH, electrostatic interaction decreased while hydrophobic interactions increased between blueberry pectin and anthocyanins, and hydrogen bond likely remained constant. Putative health benefits of anthocyanins are probably influenced by small pH and ionic strength changes in food matrixes. Image 1 • Binding sites and affinity of anthocyanins and blueberry pectins vary • Anthocyanins bound more linear and more negatively charged pectin structure • Increasing ionic strength weakens chelator fraction-anthocyanins interaction • Decreasing pH strengthens hydrophobic or π-interaction of pectin-anthocyanins [ABSTRACT FROM AUTHOR]

• Malvidin-, cyanidin-, and delphinidin-3-glucosides uniquely bind pectin fractions. • In vitro stability was highest with chelator soluble fraction and cyanidin-3-glucoside. • Chelator soluble fraction protected anthocyanin stability more than water soluble fraction. • Hydrogen bond contributes strongly to blueberry pectin-anthocyanin interaction at pH 4.0. Pectin was extracted from blueberry powder as water soluble fraction (WSF), rich in branched regions, and chelator soluble fraction (CSF), linear, with strong negative charge. Binding of pectins with three anthocyanin standards (malvidin-3-glucoside; M3G, cyanidin-3-glucoside; C3G, and delphinidin-3-glucoside; D3G) and blueberry extract (BBE) were used. Without blueberry pectin, M3G was the most stable followed by C3G, whereas D3G completely disappeared after gastrointestinal digestion. CSF prevented M3G and C3G degradation more than WSF, the in vitro stability was highest with CSF and C3G. Increased stability of anthocyanins after simulated gastrointestinal digestion suggests that anthocyanins can be transported to colon where gut microbiota actively produce anthocyanin metabolites. The amount of bound anthocyanins that interacted with blueberry pectin increased as the number of hydroxyl groups increased on anthocyanins. Hydrogen bonding in addition to electrostatic interaction contribute to stability of pectin-anthocyanins interaction at pH 4.0 and contribute to stability under gastrointestinal simulation. [ABSTRACT FROM AUTHOR]

Abstract Blueberry powder was sequentially fractionated to water (WSF), chelator (CSF) and sodium carbonate (NSF) soluble fractions. Uronic acid content was above 22 μg/mg AIS. The 4% potassium hydroxide (4KSF) and 24% potassium hydroxide (24KSF) soluble fractions were hemicellulose rich fractions. Cell wall glycan-directed monoclonal antibodies (mAbs) based glycome profiling analyses revealed that WSF, CSF and NSF fractions had epitopes of homogalacturonan (HG), arabinogalactan (AG), and xyloglucan (XG), but no xylan. 4KSF and 24KSF fractions had higher abundance of xyloglucan and xylan epitopes in addition to pectic epitopes. Arabinose and galactose were the two major neutral sugars in the WSF, CSF, and NSF. Xylose represented about 70 mol% neutral sugar in 4KSF and 24KSF fractions. Increased flexibility and presence of protein likely influence the propensity of pectin to bind anthocyanins. Graphical abstract Image 1 Highlights • Water soluble blueberry fraction has lower than 50% DE. • Water soluble fraction is rich in xyloglucans, low in homogalactan. • Chelator soluble fraction is rich in xyloglucan, rhamnogalactan and xylan. • Protein content is higher in alkali soluble fraction. • Increased protein and flexibility of pectin may increase anthocyanin binding. [ABSTRACT FROM AUTHOR]