Study On Spectroscopy And Sensing New Methods For Accurately Identifying Sesame Oil Authenticity

Sesame oil is a kind of vegetable oil with excellent flavor extracted from sesame.It is rich in a variety of active substances such as lignans,vitamin E,sesamol,etc.,which has anti-oxidation,anti-cancer and anti-aging functions.And because of its unique aroma and medicinal value,it is loved by people all over the world.At present,there are two common sesame oil production processes on the market,one is the traditional Chinese water extraction method,usually called the water extraction method,and the other is the physical pressing method.Although the pressed sesame oil(Pre-Sesame oil)obtained by pressing method and the small grinding sesame oil(AEP-Sesame oil)obtained by water extraction process both come from sesame seeds,due to the different processing technology,there are some differences in flavor,efficacy and other properties between them.Water extraction sesame oil has a higher price in the market because of its excellent flavor and complex treatment process,and the oil production rate of water extraction sesame oil is lower than that of pressing method.In the same specification and brand on the market,the price of small-milled sesame oil is 1.5 to 3 times higher than that of pressed sesame oil.In addition,the price of pressed sesame oil in China is 3 to 6times that of ordinary vegetable oil,and the price of sesame oil is 5 to 25times higher than that of other vegetable oils in South Korea(which means that the price difference between imported and non-imported oil is huge).Driven by profits,fake and shoddy sesame oil products often appear in the market.Unscrupulous merchants use pressed sesame oil with lower processing cost to pass off as small grinding sesame oil,or directly add flavors and pigments to cheap vegetable oil to pass off as high-priced sesame oil,which not only greatly reduces the nutritional value of sesame oil,but also harms the interests of consumers.Among them,the addition of flavors and pigments and unsanitary production environment will also pose a threat to consumers'health.At present,the discrimination methods of sesame oil are mainly based on artificial appearance and aroma observation,or rely on the chromatographic analysis of large instruments,so the establishment of a rapid and simple method to detect the authenticity of sesame oil has important research value and practical significance.This paper analyzes the current research status of authenticity detection methods of sesame oil in detail,and aims at the problems of unclear volatile compounds,complicated pre-processing for detection,and slow detection speed in the current research on the differences between sesame oil and cheap vegetable oils in different processes.In this paper,a series of methods for detecting the authenticity of sesame oil from large-scale chromatography-mass spectrometry instruments to medium-sized spectrometers are developed.Finally,a variety of authenticity markers targeting array sensors are constructed,and the instrument-free visual rapid detection of the authenticity of sesame oil is realized.The main research contents are as follows:(1)First,the volatile markers closely related to the authenticity of sesame oil were screened by gas phase-mass spectrometry/mass spectrometry using auto GCMS Data Anal non-target metabonomics automatic analysis strategy and partial least squares discriminant analysis(PLS-DA)and orthogonal partial least squares discriminant analysis(OPLS-DA),and the validity of the authentic markers is verified by simulating the adulteration of all kinds of sesame oil;(2)Then,quantum chemical calculations are used to screen sensing materials that can specifically respond to the authenticity markers of sesame oil,which provides a theoretical basis for the construction of sensors that quickly determine the authenticity of sesame oil;(3)Finally,based on nanoporphyrin materials and polyphenol dyes,a nano-effect ultraviolet-visible spectrum sensor and a four-channel visualization array sensor for rapid detection of the authenticity of sesame oil are constructed respectively.1.This paper first briefly describes the function and flavor of sesame oil,then summarizes the research progress and existing problems of authenticity analysis of sesame oil,and then summarizes the application of visual sensing methods in medicine and food detection.finally,in view of the existing problems in the current monitoring and analysis of the authenticity of sesame oil,this article puts forward the research ideas,research content and innovation points.2.Aiming at the common problems of cheap vegetable oil adulteration and different technology adulteration in sesame oil,the research was conducted on 24 types of sesame oil produced by different production processes(including 12 types of pressed sesame oil and 12types of small milled sesame oil)and 16 commonly used adulterated vegetable oils.First,use non-target metabolomics automatic analysis strategy and high-throughput screening of chemometric algorithms such as PLS-DA and OPLS-DA for authenticity markers used to identify sesame oil technology and cheap vegetable oil adulteration,and then use NIST library and retention index and standard solutions to identify its structure and make a quantitative analysis.At last,six key sesame oil authenticity markers were screened,namely 3-methyl-2-butanone,2-ethyl-5-methylpyrazine,guaiacol,2,6-dimethyl Pyrazine,5-methylfuran and ethylpyrazine.Among them,guaiacol mainly comes from sesame itself,and the other five compounds mainly come from Maillard reaction during the processing of sesame oil.In addition,pyrazine compounds in the authenticity markers with the largest variety and higher content are expected to play an important role in the authenticity of sesame oil.3.In order to further verify the ability of the selected authenticity markers to distinguish the adulteration of sesame oil and cheap vegetable oil.Firstly,a method for selective detection and accurate quantification of six authentic markers in pressed sesame oil,small milled sesame oil and adulterated vegetable oil was established by GC-MS/MS selective reaction monitoring technology(SRM),and then combined with PLS-DA and other chemometrics to discriminate and analyze the adulteration of sesame oil.The result showed that the accurate discrimination of pressed sesame oil,small grinding sesame oil and adulterated vegetable oil can be realized only by 6 kinds of authenticity markers,and the validity and reliability of 6kinds of authenticity markers are verified by adulteration model.4.In order to screen the sensing materials that can specifically identify the markers of the authenticity of sesame oil,by using the SciFinder's CASReact reaction information database and combined with the study of quantum chemical density functional theory to find the authenticity markers of sesame oil.It is found that the lone pair electrons of the N and O atoms in the pyrazines and phenols in the authentic markers of sesame oil can coordinate with the empty orbitals of metal ions,and porphyrin and polyphenol dyes are selected as candidate sensing materials for coordination response signal amplification by quantum chemistry calculation.Finally,through experimental verification and comprehensive analysis,it is determined that Zn²⁺in the metal ion has a better binding capacity.The result showed that porphyrins and polyphenol dyes are effective signal amplification sensing materials,which are expected to be used for rapid detection of the authenticity of sesame oil.It provides a theoretical basis for the construction of subsequent sensing methods to determine the authenticity of sesame oil.5.Based on the screened sensing materials for identifying the authenticity markers of sesame oil.On the one hand,through the mechanism of ZnTPyP optical signal changes caused by the competitive coordination of Zn²⁺in nanocrystalline zinc porphyrin(ZnTPyP)by pyrazines and other authenticity markers in sesame oil,a new method for authenticity discrimination of sesame oil based on nano-effect UV-vis spectrum sensing was constructed.The sensor can detect adulteration of sesame oil in the range of 5%to 90%,and has a good linear relationship.The method does not require complicated pre-processing steps,and simple to operate,which is expected to provide a simple,economical and effective new strategy for authenticity determination of oil crops such as medicine and food.6.Based on the sensor material that has been screened.On the other hand,through the competitive coordination of Zn²⁺with four kinds of polyphenol dyes(alizarin red S,bromopyrol red,pyrogallol red and pyrocatechol violet)and other authentic markers such as pyrazines in sesame oil,the visual effect of different color changes of polyphenol dyes can be produced,and a visual array sensor for rapid discrimination of sesame oil adulteration is established.Within the range of 5%to 90%adulteration of sesame oil,there is a good linear response between the color change signal(RGB value)of the four dyes and different adulteration concentrations of sesame oil,and visual semi-quantitative identification can be realized.Furthermore,PLS-DA and partial least squares regression(PLSR)method are used to distinguish and quantify the RGB signal,and then analyze the effect of visual color change.Among them,the accuracy of the PLS-DA model for the adulteration concentration of sesame oil is100%;the predicted value of the adulteration concentration in the PLSR model does not deviate significantly from its true value,indicating that the above model can accurately determine the adulteration concentration of sesame oil and provide reliable quantitative results.The sensor has the advantages of simple operation,rapid response and visual detection,and provides a new method for on-site instrument-free detection of sesame oil and other medicines and foods.