Effect Of Refining Process Of Evening Primrose Oil On Its Nutritional Composition And Antioxidant Performance

Evening primrose oil has a high content of various unsaturated fatty acids such as oleic acid,linoleic acid and ?-linolenic acid.It has been used as a dietary supplement for the human body,and the oil is useful for rheumatoid arthritis,atopic dermatitis and premenstrual syndrome have certain therapeutic effects.In addition,evening primrose oil also contains micronutrients such as tocopherols,total phenols,phytosterols,and squalene.Evening primrose seeds,after preliminary extraction to obtain evening primrose oil,contain undesirable impurities such as phospholipids and free fatty acids,which will affect its taste,color,and flavor,so it needs to be refined.During the refining process,while removing the bad impurities,it will also cause a large loss of micronutrients in the oil,which will affect the quality and antioxidant properties of the refined oil.Therefore,in order to make evening primrose oil moderately refined,improve the quality of oil,this paper systematically studies the changes in the physical and chemical properties and basic composition of evening primrose oil during the refining process;The change law and correlation of the antioxidant performance in the whole refining process were measured and analyzed.The specific research content is as follows:(1)Determination of the main physical and chemical indexes(acid value,peroxide value,ultraviolet absorbance,anisidine value,2-thiobarbituric acid value,iodine value and saponification value)of evening primrose oil in different refiningstages(degumming,deacidification,decolorization,deodorization and dewaxing)by the national standard method,and analyze the change rule.The results show that after the entire refining process,some indicators have changed significantly.Among them,the acid value has decreased from 1.88 mg KOH/g to 0.37 mg KOH/g,and the deacidification processes have the most significant effect on it.The peroxide value has decreased from 7.35 mmol/kg to 0.79 mmol/kg,in which the decolorization process had the most significant effect on it;the anisidine value and the2-thiobarbituric acid value showed an overall upward trend,and the decolorization process had the most significant effect on it.The iodine value and saponification value did not change significantly.Gas chromatography was used to analyze the fatty acid content and composition of the evening primrose oil during refining.The results showed that the main components of evening primrose oil were linoleic acid and ?-linolenic acid,and their contents decreased from 61.46% to 60.67%,and from12.91% to 12.58%.On the whole,the content and composition of unsaturated fatty acids in evening primrose oil did not change significantly during the entire refining process,and the decolorization process had the greatest impact on it.(2)Determination and analysis of tocopherol,total phenol,phytosterol and squalene contents of evening primrose oil at different refining stages by high performance liquid chromatography and gas chromatography.The results showed that after the entire refining process,the content of total tocopherol decreased by about21.21%,of which the loss of ?-tocopherol was the largest,down by 53.73%;the content of total phenol decreased by 79.4%,the loss was the most serious;the total plant sterol content decreased by 13.94%;Squalene content decreased by 20.19%.The deacidification and deodorization processes are the main processes leading to the loss of trace nutrients.The volatile components of evening primrose oil were analyzed by headspace solid-phase microextraction combined with gas chromatography-mass spectrometry.The results showed that 57 volatile components were detected in the evening primrose oil,which were alkane,aldehyde,ketone,alcohol and Ester compounds,etc.Among them,aldehydes and ketones have the greatest effect on the odor of evening primrose oil.The number of aldehydes and ketones increased to 16 and then decreased to 9.The decoloring and deodorizing processes have a greater impact on it.(3)The DPPH,ABTS,FRAP,and ORAC four in vitro antioxidant evaluation methods were used to determine the change of the antioxidant capacity of evening primrose oil in the refining process,and the correlation between it and micronutrients was analyzed.The results show that after chemical refining,the antioxidant capacity of evening primrose oil is on the decline,and the deacidification process has the most significant effect on it(p < 0.05).Through Pearson bivariate correlation analysis,it was found that the contents of tocopherol,total phenol,phytosterol,and squalene in evening primrose oil had a certain correlation with their antioxidant capacity.The change of total phenol content has the most significant effect on its oxidation resistance(p < 0.01).The research results of this paper can provide a certain theoretical basis for properly optimizing the refining process parameters of evening primrose oil,further improving the quality of fats and oils,and enabling better development and utilization of evening primrose oil.At the same time,it can also provide a certain data reference for scholars in the research field.