Study On Antioxidant Mechanism Of Five Flavonoids Using Quantum Chemical Calculation And Its Application In Soybean Oil

Modern medical research shows that many diseases and damage are caused by excessive free radicals in the body,so it is particularly important to seek safe and efficient antioxidants that can scavenge free radicals.Among them,flavonoids which widely distributed in plants have gradually become the focus of attention,because they have strong ability to scavenge free radicals and multiple beneficial functions.At present,the mechanism of scavenging free radicals can not be explained only by experimental methods essentially,so people turn to use quantum chemistry to explore the antioxidant capacity of substances.Among them,density functional theory(DFT)has developed into a common quantum chemical calculation method because of the advantages of short time-consuming and high accuracy.Nowadays,DFT has been reported in the field of food,such as using this theory to study the antioxidant activity of substances.Thus,this paper firstly investigated the antioxidant activity of five flavonoids including dihydromyricetin,myricetin,morin,kaempferol and galangin by DFT,which provided a new idea for exploring their antioxidant activity.Then,the antioxidant activities of the five flavonoids and synthetic antioxidants in soybean oil were compared and analyzed.The main research contents and results are summarized as follows:The structural features of five flavonoids including dihydromyricetin,myricetin,morin,kaempferol and galangin,and three possible antioxidant mechanisms including hydrogen atom transfer(HAT),single electron transfer followed by proton transfer(SET-PT)and sequential proton loss electron transfer(SPLET)were studied by DFT.Several thermodynamic parameters of five flavonoids in gaseous and solvent environments were calculated.The result showed that the antioxidant activities of flavonoids were closely related to their structures,and the antioxidant activity of five substances were different under different environments and mechanisms.HAT was the priority mechanism in the gas phase.The order of antioxidant activity of five substances from strong to weak were myricetin,dihydromyricetin,kaempferol,morin and galangin.In polar solvents,SPLET was the dominant mechanism and the order of antioxidant activity of five substances from strong to weak followed by morin,dihydromyricetin,kaempferol,galangin and myricetin.The reaction between myricetin and hydroxyl radicals(OH~·)was studied by DFT.Firstly,the Gibbs free energy of myricetin scavenging hydroxyl radicals under three antioxidant mechanisms was calculated.The result indicated that HAT was the main reaction mechanism.Then,the transition state,potential energy surface and the rate constants of reactions between phenolic hydroxyls in myricetin and OH~·radicals were calculated.The result showed that 4'-OH required the lowest activation energy and had the highest reaction rate constants and the strongest reaction activity.To verify the antioxidant effect of the above five natural antioxidants in practical applications,myricetin,dihydromyricetin,morin,kaempferol and galangin were added to soybean oil respectively.The changes of peroxide value and anisidine value were measured after 15 days of accelerated oxidation.The results manifested that myricetin and dihydromyricetin had good antioxidant activity and could be used as good substitutes for synthetic antioxidants.