| Edible vegetable oil is extracted from plant fruits,seeds or other parts and is an indispensable part of human diet.Its quality and safety are a hot issue of public concern.In recent years,there have been frequent incidents of adulteration of edible oil in our country.Although relevant laws and regulations,national standards,and detection methods are gradually being improved,some low-quality false negative oils are still mixed into the market.Therefore,the development of a fast,accurate,and highly sensitive method for evaluating the quality of vegetable oil is still the key task of current edible vegetable oil quality control.In this study,the main components of peanut oil,corn oil,soybean oil,rapeseed oil and sunflower oil,including fatty acids,sterols,volatile flavor components and other unsaponifiables were used as the research object.A series of edible vegetable oil quality evaluation methods were established by using chromatography technology,including the fatty acids,sterols,volatile flavor components and other unsaponifiables of edible vegetable oils.Moreover,a qualitative and quantitative analysis of adulterated peanut oil was carried out by the combination of fatty acid composition and chemometrics.The main research contents and results were as follows:(1)Headspace-solid phase microextraction(HS-SPME)combined with comprehensive two-dimensional gas chromatography-quadrupole time-of-flight mass spectrometry(GC×GC-Q-TOF/MS)was used to analyze the volatile flavor components of five kinds of edible vegetable oils.In order to obtain more volatile components,the column system of comprehensive two-dimensional chromatography and the conditions of solid-phase microextraction were investigated.The results showed that when the column system was HP-5MS as the one-dimensional column,DB-17 MS as the two-dimensional column,the extraction fiber head coating of SPME was 50/30 ?m DVB/CAR/PDMS,the sampling volume was 3.0 m L,the extraction time was 30 min,the extraction temperature was 85 ?,and the resolution time was 5 min,the analysis effect was the best.(2)A total of 115 components and 11 types of components were detected in the five edible vegetable oils,and their distribution in the five edible vegetable oils was significantly different.Among them,a total of65 components were detected in peanut oils,33 components were detected in corn oils,57 components were detected in rapeseed oils,53 components were detected in soybean oils and 50 components were detected in sunflower oils.The volatile components in peanut oils were mainly aldehydes,pyrazines,and furan compounds.The content of pyrazine compounds was significantly higher than that of the other four vegetable oils,accounting for 34.800% of the total detections.The volatile components identified in corn oils,soybean oils and sunflower oils were mostly aldehydes.Among them,the relative content of hexanal in various edible vegetable oils was relatively high,namely: sunflower oils 15.528%,soybean oils 14.282%,and corn oils 12.873%.The volatile components identified in rapeseed oils were mainly aldehydes,nitriles and pyrazines.Nitriles were the special volatile components in rapeseed oils,which could be used as the characteristic component of rapeseed oils to distinguish it from other vegetable oils.(3)Gas chromatography methods were used to analyze the derivatized fatty acids and sterols in five kinds of edible vegetable oils.The results showed that there were great differences in the composition and content of fatty acids and sterols among the five edible vegetable oils.The content of oleic acid in peanut oils was the highest,which was39.472?62.454%.Corn oils,soybean oils and sunflower oils had the highest content of linoleic acid,which were 56.083?57.187%,51.547?54.563%,53.041?63.444%,respectively.Except for oleic acid and linoleic acid,traditional rapeseed oils had higher erucic acid content,reaching 7% or more,which could be clearly distinguished from the other four kinds of edible vegetable oils.The sterols of five kinds of edible vegetable oils were mainly composed of rapeseed sterol,stigmasterol and?-sitosterol.In addition,rapeseed oils also contained a small amount of rapeseed sterol.Among the five kinds of oils,corn oils and rapeseed oil had the highest total sterol content,which were 648.663?778.821 mg/100 g,610.656?731.272 mg/100 g,respectively.The total sterol content of peanut oil was the second,which was 132.528?315.504 mg/100 g.The total sterol content of soybean oils and sunflower oils were the lowest,which were 215.301?271.687 mg/100 g and 243.558?281.831 mg/100 g,respectively.Hierarchical cluster analysis(HCA)was used to analyze the fatty acid and sterol composition data of five kinds of edible vegetable oils.The results showed that the fatty acid composition of peanut oils was significantly different from corn oils,soybean oils,and sunflower oils,and the sterol composition was different from rapeseed oils and corn oils.Therefore,analysis based on the composition of fatty acids or sterols could be used as one of the effective means to identify peanut oil adulteration.(4)The peanut oil samples adulterated with different proportions of soybean oil were detected by gas chromatography,and when combined with linear discriminant analysis(LDA)to discriminate and classify the adulterated oils with the adulteration ratio of 6-80%(w/w),the accuracy of the discrimination reached 100%,indicating that the established linear discriminant analysis function was effective and could be used for the qualitative identification of unknown adulterated peanut oils.Multiple linear regression(MLR),partial least square regression(PLSR)and artificial neural network(ANN)were used to construct a quantitative analysis model of adulteration,and evaluate the model by comparing the model adulteration limit with the root mean square error(RMSE).The results showed that the established ANN model has a lower limit of adulteration determination and a smaller RMSE,which was more suitable for quantitative screening and identification of adulterated peanut oils.(5)Ultrasound-assisted saponification-liquid-liquid extraction combined with high performance liquid chromatography was used to analyze the unsaponifiables of five kinds of edible vegetable oils,including peanut oils,corn oils,soybean oils,rapeseed oils and sunflower oils.It was found that when the detection wavelengths were 280 nm and443 nm respectively,the distribution of 2-(1-hydroxy-4,6-dimethyl-4,6,8-decatrienyl)-dehydrodundiola(HDDD)and lutein in rapeseed oils were significantly different from their distribution in peanut oils,and HDDD is a characteristic component of rapeseed oils.The analysis of pure vegetable oil samples found that the content of lutein in peanut oils was less than or equal to 6.186 ?g/g,the content of lutein in rapeseed oils was33.664?342.689 ?g/g,and the content of HDDD in rapeseed oils was71.922?97.010 ?g/g,while it was not detected in all peanut oils samples.The HDDD in rapeseed oil was used as a marker and lutein was used as a supplementary evidence to establish an adulteration judging method,which adulteration judgment limit was as low as 0.4%(w/w).The method was used to screen adulterated peanut oils,and the results showed that the adulteration judging method could not only successfully screen adulterated peanut oils,but also predict the lowest adulteration ratio of rapeseed oils in adulterated peanut oils,and its prediction accuracy was up to 86.7% or more. |
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