The isolation of anthocyanin monomers from blueberry pomace and their radical-scavenging mechanisms in DFT study

Abstract

This study explored the isolation of anthocyanin monomers using a medium- and high-pressure separation technique as a means to increase the added value of a by-product of the blueberry juice industry. Six anthocyanin monomers were isolated with a purity of 95% and identified as mono-galactoside, glucoside, and isomers of delphinidin, malvidin, and even malvidin-3-O-arabinoside, malvidin-3-(6″-acetyl)-O-glucoside by LC-MS and ¹H NMR. Following the conformation search, the computer calculation manifested the active sites of six anthocyanins (C_4'-OH) and their stabilities based on the structural and energy parameters. The DPPH tests demonstrated that delphinidin glycoside's free radical scavenging ability (89.93 ± 2.03 % and 86.50 ± 3.16 %) was significantly higher than that of malvidin (80.39 ± 1.30 % and 81.02 ± 0.45 %), and that malvidin's capacity was improved by conjugation arabinoside (87.48 ± 2.39 %) and acetylated glucoside (88.39 ± 1.37 %), which was compatible with the computer calculation.

Keywords: Anthocyanin monomer; Blueberry pomace; Density functional theory; Isolation and identification; Scavenge free radical capacity.