Doctor of Philosophy (PhD)
School of Nutrition and Food Sciences
Blueberry pectins were sequentially extracted from highbush blueberry powder and precipitated in alcohol to obtain water soluble fraction (WSF) and chelator soluble fraction (CSF). WSF was high methoxyl pectin (degree of esterification: 53), rich in in neutral sugars (40 mol%), and had less negative charge (-21 mV) whereas CSF was low methoxyl pectin (degree of esterification: 21), rich in uronic acids (92 mol%), and had lower negative charge ( -26 mV).
The stability of blueberry pectin-anthocyanin complex was investigated under simulated in vitro digestion. Binding of blueberry pectins with three anthocyanin standards (malvidin-3-glucoside; M3G, cyanidin-3-glucoside; C3G, and delphinidin-3-glucoside; D3G) and blueberry powder extract (BBE) were used. M3G was the most stable followed by C3G, whereas D3G completely disappeared after gastrointestinal digestion. CSF bound and prevented M3G and C3G degradation more than WSF. 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. This suggests that hydrogen bonding in addition to electrostatic interaction contribute to stability of pectin-anthocyanins complexes at pH 4.0.
A binding selectivity between blueberry pectin and anthocyanins was determined by Langmuir isotherm. CSF had four times higher (R2 > 0.94) adsorption with anthocyanins whereas WSF had less and variable interaction with anthocyanins. Further binding study influenced by exogenous factors showed that blueberry pectin-anthocyanins adsorption was the highest at pH 3.0 and the least at pH 4.0 regardless of the ionic strength. Increasing ionic strength weakened the pectin-anthocyanin interaction between pH values 3.0 and 4.0, however, no significant difference was observed at pH 2.6. As pH value changed from 4.0 to lower pH values, electrostatic interactions were less dominant while hydrophobic and hydrogen interactions contributed more to blueberry pectin and anthocyanins.
Koh, Jee Won, "Blueberry Pectin-Anthocyanin Binding Kinetics and Stability Under In Vitro Digestion" (2019). LSU Doctoral Dissertations. 4843.