4^th International Food Safety, Quality & Policy Conference

Anthocyanidins are flavonoid natural products responsible for the red to purple colours of many vegetables, fruits and flowers. Because of their poly-phenolic nature, they possess good antioxidant activity where some of them are more potent antioxidants than vitamins E and C which enables them to provide protection against many chronic diseases. Most experimental works have observed improved antioxidant activity as a result of the presence of 3-hydroxyl group and/or catecholic moiety that can donate two-hydrogen atoms and forms stable quinones. DFT calculation was performed to identify the favored path of the two-hydrogen atom donation process and determine the roles of the 3-hydroxyl group and other OH and OMe groups in stabilizing the resulted radicals and thus controlling the antioxidant efficiency in a series of 3-oxy-(and de-oxy) anthocyanidins with catecholic and non-catecholic moieties. Results showed that all 3-oxyanthocyanidins were nonplaner while their 3-radicals were planer that allows better unpaired electron delocalization and explains the lowest BDE of 3-OH group in all the examined anthocyanidins. In non-catecholic compounds, the presence of two stabilizing OMe groups ortho to 4’-OH causes the two-hydrogen atom donation to take place through 3, 4’-OH; otherwise, the donation occurs through 3, 5-OH. In all catecholic anthocyanidins, it was found that two-hydrogen atom donation through 3, 4’-OH path was more favored than that of the catecholic hydroxyl groups (4’, 3’-path) by 10-23 Kcal/mol while the role of the catecholic 3’-OH is stabilizing 4’-radicals by H-bonding. HOMO and spin density distribution supported the stabilization of 3, 4’-diradicals.