Investigation On Antioxidant Activity Of Gallate Esters And Its Interactions With ?-tocopherol In Oil-in-water Emulsions

Lipid oxidation has been the main factor affecting the oxidative stability of emulsions.The addition of antioxidants is the main method employed for preventing lipid oxidation in emulsions.In order to improve the acitivities of single antioxidant,more and more studies have been focused on the combination usage of two or more different antioxidants.In this research,the antioxidant activities of different polarity gallates in corn oil O/W emulsion have been compared.Based on this,the interaction effects between gallates and?-tocopherol in emulsions were further studied.The main results are as follows:?1?High pressure homogenization was used to prepare corn oil O/W emulsion.Tween 20 was added at different mass concentration to investigate their effects on size and?-potential of the emulsion droplets.Results show that the best mass concentration of Tween 20 used in emulsion is 0.1%.Mass concentration of 0.1%Tween 20 was used to prepare emulsions.The effects of antioxidants on the size,?-potential of the emulsion droplets was studied.Results show that emulsion particle size become smaller as gallate and?-tocopherol were added.However,particle size is irrelevant to antioxidants'concentration and variety.But?-potential of the oil droplets were related to the hydrophobicity of antioxidants and reduced as the concentrations of antioxidants decrease.?2?Lipid peroxide value and hexanal formation in the O/W emulsions were determined by UV-Vis and headspace injection-GC-MS and used to estimate the antioxidative ability of different polarity gallates.The results contradicted with"polar paradox theory"showed that the order of antioxidative ability of antioxidants in the emulsion is:R3>R12>R8>R0>R18.Fuether using HPLC and Further using HPLC and 16-ArN₂⁺probe to detect the distribution of antioxidants in the water phase and interfacial layer of emulsions.The results showed that the antioxidant activities of antioxidants in the emulsion were associated with their distribution.If the antioxidants distribute more in the interfacial layer,the antioxidants show higher antioxidative ability in the emulsion.Therefore,the antioxidant activities of antioxidants in the emulsion are not only related to their polarity,but also associated with their distribution.?3?The combinations of gallates and?-tocopherol were investigated in emulsions.Lipid peroxide value,hexanal formation and interaction index were determined to estimate the interactions between different polarity gallates and?-tocopherol.The results showed that R3,R8 and R12 had antioxidant synergy with?-tocopherol.R18showed significant antagonistic effect with?-tocopherol.The combination of propyl gallate and?-tocopherol?T-R3?showed the most strongest synergistic effect.Based on this,the distributions of antioxidants in the emulsion,fluorescence quenching of gallates and?-tocopherol,oxidation peak potential of gallates and?-tocopherol and depletion of gallates and?-tocopherol were further studied to investigate the interactions between gallates and?-tocopherol in emulsions.We found that the interactions between gallates and?-tocopherol in the emulsion is closely related with their distributions in emulsions.If antioxidants distribute more in the interfacial layer,the antioxidants show higher synergistic effect in the emulsions.Redshift amount was in the order of:R3>R8>R12>R18>R0;Ks value of gallates was in the order of:R3>R8>R12>R0>R18;K_A value of gallates was in the order of:R18>R3>R8>R12>R0;K value of gallates was in the order of:R3>R12>R0>R8>R18.Therefore,considering fluorescence quenching efficiency?Ks?,efficiency of fluorophore quenching of non-radiative energy transfer?K?and intensity of bindingforce and affinity?K_A?between gallates and?-tocopherol.We found that propyl gallate showed strongest interaction with?-tocopherol.Oxidation peak potentials of gallates and?-tocopherol were studied in acetonitrile,phosphate buffer and Tween20 micells.The oxidation peak potential of gallates were higher than?-tocopherol in these three systems.Therefore,?-tocopherol is thermodynamically preferred to donate electrons to gallates.Using HPLC to study depletion of?-tocopherol,gallic acid,and its alkyl esters during oxidation of O/W emulsion.Results showed that?-tocopherol quione was the oxidative product of?-tocopherol.The combination of gallic acid and?-tocopherol didn't show synergistic effect.During the oxidation of the emulsion combined addition of propyl gallate and?-tocopherol,propyl gallate is preferentially oxidized and?-tocopherol were regenerated by propyl gallate.Based on this regeneration process,the combination of propyl gallate and?-tocopherol showed synergistic effect.