Catechinic compounds suppress free radicals in camellia oil by donating hydrogen atoms: quantum chemistry calculation combined with EPR detection

Phenolic compounds have been serving as primary antioxidants in retarding lipid oxidation, however, the conventional method for screening phenolic candidates is time-consuming and costly. In this study, phenolics were selected in accordance with the bond dissociation energy (BDE) of O−H and the Gibbs free energy change (ΔG) of the scavenging reaction via quantum chemistry calculation, the efficiency of selected phenolics was subsequently assessed by free energy barrier (ΔG‡), eventually, the suppression efficiency of the candidates was verified by using electron paramagnetic resonance (EPR) determination. Among six catechinic compounds, (−)-gallocatechin gallate (GCG) and (−)-epigallocatechin gallate (EGCG) were identified as the most promising candidates, both of which showed potential efficiency for scavenging alkyl peroxyl (•OOR), alkoxyl (•OR), oleic acid (•OA-C11) and linoleic acid (•LA-C11) radicals. In the thermally-induced camellia oil model (180 °C, 20 min), the inhibition rates of EGCG against alkyl (•R), alkoxyl (•OR) and DMPO oxidative free radicals (•X) were 60.06 ± 0.38 %, 59.74 ± 2.57 % and 92.05 ± 1.70 %, respectively, analogously, the efficiencies of GCG scavenging these radicals ranged from 68.40 ± 0.82 % to 94.27 ± 0.33 %. This indicates that the proposed methodology can effectively screen lipid antioxidants, furthermore, both GCG and EGCG are capable of retarding oxidation in camellia oil.