| Oil-in-water(O/W)emulsion is a common form of food in the food industry,which is prone to lipid oxidation.α-Tocopherol and γ-oryzanol are natural lipid concomitants,which have good effects to inhibit the oxidation.Previous studies of our team have shown that α-tocopherol and γ-oryzanol had antioxidant interactions in different media,and the mechanisms were different.However,the existence of antioxidant interactions and the antioxidant mechanism in O/W emulsion is not yet clear.Besides,O/W emulsion is a multiphase system,the interaction of antioxidants may be affected by their polarity,hydrophobicity and other factors.Based on this,this paper used high-pressure homogenization to prepare rice bran oilin-water emulsion,and explored the type and mechanism of antioxidant interaction between α-tocopherol and γ-oryzanol in O/W emulsion.The specific contents were as follows:Firstly,high-pressure homogenization was used to prepare O/W emulsions with separate and compound addition of α-tocopherol and γ-oryzanol,and their effects on the physical and chemical properties,as well as the oxidation stability of the emulsion were evaluated.The results showed that,the concentration of α-tocopherol and γ-oryzanol had no significant effect on the physicochemical properties of the emulsion(p>0.05),such as particle size and zeta potential,and the physical and chemical properties of O/W emulsion were stable within 15 days.Compared with the blank,α-tocopherol and γ-oryzanol could significantly improve the oxidation stability of O/W emulsion(p<0.05).However,α-tocopherol had no effect on the oxidative retention time of lipid hydroperoxide,only γ-oryzanol at 240 μmol/L could extend for 7 days,besides,α-tocopherol and γ-oryzanol prolonged the oxidation retention time of hexanal by 8 days and 2 days,respectively.This proved that α-tocopherol and γ-oryzanol had different degrees of antioxidant activity in O/W emulsions.After the compound addition of α-tocopherol and γ-oryzanol,the oxidation lag time of lipid hydroperoxide was not prolonged,and the oxidation residence time of hexanal was 6 days earlier than that of α-tocopherol alone,which indicated that the antioxidant effect of the compound addition of α-tocopherol and γ-oryzanol in O/W emulsion was weaker than that of the separate addition.Secondly,the centrifugal separation method was used to explore the phase distribution ofα-tocopherol and γ-oryzanol in O/W emulsion,and their interaction type in O/W emulsion was calculated.The results showed that,when α-tocopherol and γ-oryzanol were added to the O/W emulsion separately,they were distributed in different phases of the emulsion,where α-tocopherol was mainly distributed in the emulsion interface or inside the lipid droplets,γ-oryzanol was mainly distributed in the water phase,but after compound addition in O/W emulsion,α-tocopherol gradually migrated to the water phase,making the concentration of α-tocopherol in the water phase increased,while γ-oryzanol remained in the water phase;Further,using the Jin’s Q method showed that,the interaction index of α-tocopherol and γ-oryzanol at four concentrations was less than 1,which showed antagonistic effect,and the interaction index decreased significantly with the concentration increased(p<0.05).In terms of hexanal content,the interaction index of α-tocopherol and γ-oryzanol at the four concentrations was close to zero,but the concentration had no significant effect on the interaction index(p>0.05).Finally,the fluorescence quenching method and cyclic voltammetry were used to explain the interaction mechanism of α-tocopherol and γ-oryzanol in O/W emulsion.The fluorescence quenching results showed that,in the O/W emulsion,as the concentration of γ-oryzanol increased,the fluorescence intensity of α-tocopherol decreased gradually,and the maximum fluorescence emission wavelength(λem)of α-tocopherol had a red shift,and the degree of red shift was positively correlated with the concentration of γ-oryzanol,which preliminarily confirmed that γ-oryzanol and α-tocopherol had interaction in O/W emulsion,and the interaction was caused by the non-radiative energy transfer between γ-oryzanol and α-tocopherol within a certain distance,which led to the occurrence of static fluorescence quenching;The redox potential results showed that,because the redox potential of γ-oryzanol was higher than that of α-tocopherol,γ-oryzanol with the higher redox potential could inhibit the regeneration of α-tocopherol,thus produced no radiative energy transfer to α-tocopherol and γ-oryzanol in O/W emulsion,or because α-tocopherol regenerated γ-oryzanol,which led to the antagonism between them;The monitoring results of the oxidation process of α-tocopherol and γ-oryzanol showed that,the consumption of γ-oryzanol was unchanged when α-tocopherol was present,however,in the presence of γ-oryzanol,the consumption rate of α-tocopherol increased,indicating that the electron transfer mechanism between α-tocopherol and γ-oryzanol was not that α-tocopherol regenerated γ-oryzanol,but that γ-oryzanol inhibited the regeneration of α-tocopherol,resulting in antagonistic effect;DPPH free radical electron spin resonance monitoring results showed that,in a single α-tocopherol free radical solution,α-tocopherol free radicals could be regenerated into α-tocopherol,thus the DPPH free radical scavenging rate increased,but after adding different concentrations of γ-oryzanol,the scavenging rate of DPPH free radicals was significantly lower(p<0.05),which proved that γ-oryzanol inhibiting the regeneration of α-tocopherol free radicals into α-tocopherol,thus led to the antagonism betweenγ-oryzanol and α-tocopherol.In summary,when α-tocopherol and γ-oryzanol added separately in O/W emulsion,they could exert their antioxidant capacity at different positions of the O/W emulsion.However,after compound addition in O/W emulsion,since γ-oryzanol with a higher redox potential inhibited the regeneration of α-tocopherol,which promoted the gradual migration of α-tocopherol to the water phase,accelerated the consumption rate of α-tocopherol,resulting in antioxidant antagonistic effect.This study clarified the interaction mechanism of α-tocopherol and γ-oryzanol in O/W emulsion,and provided theoretical support for guiding the research and development of related products. |
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