Study On The Enzymatic Oxidation Of Tocopherols In Corn Germ Pretreatment And Its Relation With Oil Color Reversion

During storage,transportation,and sales,the color of refined oil has significantly deepened over time,which is termed as color reversion.This phenomenon is affected by many factors including raw material quality,refining process,and storage environment.The oxidation of ?-tocopherol is the primary factor which causes the oil color reversion However,the cause of oxidative degradation of ?-tocopherol during oil pretreatment and its relationship with subsequent color reversion are still unclear.Therefore,present research was carried out to study the characteristics of ?-tocopherol and its enzymatic oxidation during corn germ pretreatment.Further,we discussed the relationship between the enzymatic oxidation of tocopherol and the color reversion in combination with the changes of the reaction products.The main research contents are as follows:Initially,the effects on the basic physical and chemical indexes and trace components of corn oil before and after crushing were investigated(mainly the change of tocopherol content)by changing the moisture content of corn germs before and after crushing and high temperature pretreatment.The results showed that the degree of crushing affected the content of tocopherol.The higher the degree of crushing,the lower the content of tocopherol.Further,before and after crushing and rolling the germ,adjusting the moisture content and high temperature pretreatment have different effects on the quality of the crude oil and the content of tocopherol:adjusting the moisture content and high temperature treatment before crushing significantly affected the acid value,color and tocopherol content of the crude oil.When the moisture content increased from 5% to 25%,the acid value increased by 0.4 mg KOH/g,and the R value increased from 2.5 R to 3.3 R,tocopherol content decreased by 31.35 mg/kg.After dry heat treatment at 100 ?,acid value decreased by 0.51 mg KOH/g,color and luster decreased by 1.2R,tocopherol content increased by 146.92 mg/kg.However,when moisture content adjustment and high temperature pre-treatment after crush.the treatment did not significantly affect the acid value,color,and tocopherol content.Combined with the experimental results,we speculated that the enzyme reaction occurred during the crushing process.Secondly,by constructing an enzyme reaction,we verified the catalytic effect of germ homogenate on tocopherol,and carried out preliminary verification of the enzyme and its relevant properties.The results showed that corn germ homogenate can catalyze the degradation of tocopherol in the presence of phospholipids,and the reaction time was 24 h.Moreover,results showed reduced tocopherol content by 60.6%,and the catalytic activity of fresh germ was observed to be significantly higher than that of semi-dry degerming embryo(p<0.05).Investigation in the properties of tocopherol oxidase showed that the optimal pH of the enzyme was 4.5,and the optimal temperature was 20?.Moreover,the concentration of 1.0 mM ascorbic acid had a strong inhibitory effect on the enzymatic reaction(inhibition rate 96.8%).Finally,the laboratory-based method was used to synthesize the quinones and dimers of the tocopherol oxidation product.Further,the comparison of the liquid chromatograms was used to determine the composition of the product obtained through the enzyme-catalyzed reaction.Some greases returned to the path.The results showed that after enzyme-catalyzed reaction,?-tocopherol dimer product with m/z 831 was mainly obtained.When the reaction time was extended to 72 h,substances such as tocoquinone and tocored appeared,however,the content was very low.This was not convenient for quantification of the enzyme reaction and analysis.Dimers and fertility red can be detected in the oils of different refining sections.Among them,dimers had the lowest content in crude oil,and the most in deacidified oil,which was 36% higher than the crude oil.The decolorization and deodorization were slightly reduced.The content of Fertility Red was the highest in crude oil,and it continues to decrease during the degumming and deacidification process.The content in the decolorized oil reached the lowest level,which was 86% lower than that of the crude oil,and rebounds slightly after deodorization.Altogether,the oil color reversion process began with the oxidation of tocopherol in the crushing process.With the participation of phospholipids,first it was oxidized by enzymes to produce dimers and tocored and other oxidation products.Further,we observed content change during the refining process.During the storage of fats and oils,the oxidation products of the fats themselves were further combined with the oxidation products of tocopherols to form colored substances,resulting with noticeable change in the color of the oil.In summary,the existence of an enzyme that can catalyze the degradation of tocopherol in corn germ had been verified in this study.The basic physical and chemical properties of the enzyme provided practical means for inhibiting the oxidation of tocopherol in the actual production process.For the comparison of the products catalyzed by the enzyme tocopherol and the related substances for color reversion,a supplementary explanation is provided for the color reversion path.