Study And Identification On The Quality Characteristics Of Refined Evening Primrose Oil

This study is affiliated with the Science and Technology Development Project of Jilin Province（No.20210301058NY）.Unsaturated fatty acids of evening primrose oil can prevent certain diseases such as eczema,arthritis and premenstrual syndrome.As a result,the price of evening primrose oil is rather high,some unscrupulous businessmen by adulterating it to make profits.Such adulteration could jeopardize consumer confidence in the product and reduce the competitivity of evening primrose oil in the market.In this study,physicochemical parameters of evening primrose oil were first determined at each refining stage,followed by the determination of chroma,viscosity values and thermodynamic parameters.The fatty acid composition,volatile substances and oxidation stability of evening primrose oil were studied by gas chromatography-mass spectrometry（GC-MS）and Rancimat oil oxidation stability analyzer.Pearson correlation analysis was used to investigate the potential relationship between fatty acid composition and physicochemical parameters,volatile substances and oxidative stability.Finally,a model for the identification of adulterated evening primrose oil was developed using chroma,viscosity,thermodynamic parameters,fatty acid composition and infrared spectra as indicators,and chemometrics was used to determine the identification effect.The main research and conclusions are as follows:（1）The physicochemical parameters of the different refining stages of evening primrose oil（crude,degummed,alkali,bleached,deodorised and finished oils）were determined according to the method in the National Standard.The acidity,iodine,peroxide and anisidine values of evening primrose oil at each refining stage can be served as indicators to judge evening primrose oil due to significant differences.The L^*of evening primrose oil increased significantly at each refining stage,while the a^*and b^*decreased significantly,making it possible to distinguish the evening primrose oil by the chroma.Viscosity can be utilized as a determining factor because it was constant for all oil samples but varied when the shear rate rose to 20 s^-1.The cooling and melting curves of evening primrose oil had significantly distinct crystallization points,peak heights,and transition ranges at each refining stage,indicating that differential scanning calorimetry may be utilized to identify evening primrose oil.（2）By using GC-MS,the primary fatty acids of evening primrose oil were discovered to be linoleic,γ-linolenic,palmitic,oleic and stearic acids,withγ-linolenic acids serving as the distinctive fatty acids.In addition,7 fatty acids that were not commonly found in other evening primrose oil experiments were detected.Pearson correlation analysis further showed that heptadecanoic acid,stearic acid,oleic acid,linoleic acid,nonadecanoic acid,eicosatrienoic acid and erucic acid were significantly correlated with the physicochemical indices of evening primrose oil,suggesting that these fatty acids were closely related to oil quality.157 volatiles were identified in evening primrose oil by headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry,31 of which were common to all refining stages,with hydrocarbons and aldehydes dominating.Hydrocarbons were the main volatile compounds in the first three stages;hydrocarbons and aldehydes were the main components of the decolorized oil;the main components of the deodorized oil were hydrocarbons,aldehydes and ketones;aldehydes made up the largest proportion of the finished oil,followed by hydrocarbons and ketones.The principal component analysis（PCA）and hierarchical cluster analysis（HCA）were both classifying evening primrose oil at each stage of refining into 4 categories based on volatile substances:crude oil,degummed oil and alkali-refined oil as one category,the remaining oils were in their own category.In PCA,2,2-dimethylhydrazone-2-nitrobenzaldehyde and 1-（4-cycloocten-1-yl）-1-propanone were positively correlated with the finished oil;in HCA,the characteristic volatile compounds for each type of oil are mainly aldehydes,ketones and alcohols.In this study,the oxidative stability of evening primrose oil was expressed in terms of oxidation induction time（OIT）and the OIT decreased by 75%for every 20℃ increase in temperature.The higher the degree of refinement and the higher the OIT,the better the oxidative stability.At a Pearson correlation significance level of 0.05,2-ethyl-butyraldehyde and 2-nonanone were negatively correlated with the OIT of evening primrose oil,and undecanal and 6,10,14-trimethyl-2-pentadecanone were significantly positively correlated.At a significance level of 0.1,four and two aldehydes and ketones were added that were significantly positively correlated with OIT at 80℃ and 100℃,respectively;the aldehydes that were significantly positively correlated with the OIT at 120℃ increased by six,and ketones increased only with 2,3-octanedione.（3）Using chroma,viscosity and thermodynamic parameters as indicators,only qualitative analysis was possible to identify evening primrose oil adulteration model.The HCA of the oil adulteration model,using fatty acids as an indicator,was able to distinguish peanut oil with>10%adulteration and sunflower oil with>20%adulteration.Cosine similarity analysis of the adulteration model was carried out using the 11 and 7 indicators obtained from the HCA.The results were consistent with those of the HCA.Finally,the infrared spectra of the adulterated oil model in the range of1500-600 cm^-1 were analyzed using PCA and the identification results were better for identifying adulterated sunflower oil.