| The oxidation of edible oil is mainly based on auto-oxidation,which is a typical free-radical chain reaction.The traditional methods for studying the oxidation of edible oils are mostly based on the detection of oxidation products,which is an indirect study.Besides,a large part of the research is on the accelerated oxidation of edible oils at high temperatures.Electron paramagnetic resonance(EPR)technology,as the most direct and effective method for detecting free radicals,has great potential in the study of lipid oxidation.The EPR technology is used to monitor the changes of free radicals in edible oil during oxidation at room temperature,which is helpful to improve the understanding of the room-temperature oxidation of edible oil.Oxidation of oils at room temperature is generally considered to be caused by unsaturated fatty acids.Therefore,this study used common unsaturated fatty acids and edible oils as research objects,and used EPR technology to explore the formation of free radicals in normal temperature oxidation,and obtained the following results:(1)The auto-oxidation of oleic acid at room temperature mainly produces four kinds of free radicals,R·,RO·,ROO· and DMPO-X,respectively,and the total amount of free radicals has been in a certain fluctuation state.The free radical species in the oxidized linoleic acid is the same as the oleic acid.Under the same detection conditions,the free radicals in linolenic acid are mainly composed of R·.(2)In the early stage of oxidation of fatty acids at room temperature,the addition of VE and TBHQ will inhibit the formation of free radicals in the sample,resulting in the EPR spectrum signal being too low to fit or the content of RO· and ROO· is extremely low.Moreover,these two additives may act as antioxidant by providing hydrogen atoms to combine with free radicals,reducing the amount of RO· and ROO· in the system to terminate chain transfer.Adding ADVN to fatty acids introduces free radicals in the inorganic carbon center in the system and induces the production of RO·.Due to the impure chlorophyll extract and the free radical priming of chlorophyll,the total free radical level of the chlorophyll-added fatty acid samples was relatively high.(3)The oxidation rate of 4 edible oils was ranked as follows: linseed oil>peanut oil>sunflower oil>camellia oil.Linseed oil has a high degree of unsaturation and mainly forms four kinds of free radicals when oxidized at room temperature.The free radical content is ranked as follows: DMPO-X>RO·>R·>ROO·,and the order of free radicals in peanut oil is the same.The free radicals in sunflower oil are sorted according to content:RO·>DMPO-X>R·>ROO·.The free radicals in tea seed oil are mainly RO·,DMPO-X is second,and the amount of ROO· is the least.(4)Different treatment conditions have different effects on the oxidation of linseed oil.Protecting against light and adding TBHQ can significantly reduce the oxidation rate of linseed oil.Linseed oil mainly forms four kinds of free radicals when oxidized in the dark,which is the same as under light,but there is a big difference in the number of free radicals.The free radicals in linseed oil are sorted according by the content : RO·>DMPO-X>R·>ROO·.The addition of TBHQ can block the chain reaction of free radicals by reducing the number of RO· and ROO·.The effect of VE on linseed oil has two sides.Due to its strong oxidation resistance in the early stage of oxidation,the peroxide value of VE-added linseed oil is the lowest among all samples,while in the middle and late stages of oxidation.The oxidation product of VE accelerates its oxidation,resulting in a large increase in the total number of spins and PV values.The addition of ADVN results in an accelerated rate of oxidation of the linseed oil.Linseed oil supplemented with ADVN contains only three free radicals in the initial stage of oxidation,namely DMPO-X,inorganic carbon center radicals and R·.ROO· began to appear in the mid-oxidation system,and RO· began to appear in the late stage of oxidation. |
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