Study On The Refractive Index And Dispersion Characteristics Of Edible Oils

At present,there are many methods and scattered indicators for testing the safety of edible oils,the stability of testing results is not high,and there is no perfect industry standard.Therefore,an effective system for edible oil safety testing must be constructed as soon as possible in order to be beneficial to the national livelihood.This thesis focus on exploring the variation of refractive index of edible oils with wavelength and studying the dispersion characteristics of edible oils in the OCT system to obtain the characteristic index or even system for the identification of various edible oil products.This thesis takes Luhua brand peanut oil,Hujihua brand peanut oil,Golden Dragon Fish Brand rapeseed oil,Fulinmen brand rapeseed oil,and kitchen waste oil(Luhua brand peanut oil for repeated frying)as the studying objects.The refractive index characteristics of the oil at λ∈(380,1500)nm were studied by spectroscopic method,Hilbert transforms and FFT transform methods are used in OCT to perform deconvolution numerical dispersion compensation of 5 kinds of oil products,and use the Calisisto SD-OCT experimental platform to obtain the dispersion characteristics of the above oils.The main contents and results are the following four points.(1)A double glass sheet holding device was fabricated,the refractive index equations of the device and the oils were deduced,and the reflection and transmission spectrum of the above five oils needed to be measured with a spectrophotometer.It was found that the spectrum of these five oils were similar in the 380～1500 nm band,and there were characteristic absorption peaks at 930 nm,1050 nm,1210 nm and 1400 nm,which reflected the existence of many identical molecular functional groups in different oils.(2)The refractive indices of the above five oils of λ∈(380,1500)nm were modeled based on the spectrophotometer-mathematical analytical expressions and Cauchy matrix.Their refractive indices n ∈(1.37,1.52)and show normal dispersion characteristics;it is found that the refractive index with wavelength characteristic curves among the oils have high similarity,but the refractive index Cauchy matrix of each oil is different,especially in the near infrared band,the Cauchy matrix of healthy oil and waste oil are significantly different.(3)Using the above refractive index model for each oil,numerical dispersion compensation is achieved for the oil in OCT;the axial resolution of OCT is effectively improved by more than 40%;the dispersion of the oil has almost no effect on the phase spectrum,but enhances the amplitude spectrum;the improvement of the axial resolution and the enhanced amplitude spectrum make the OCT imaging depth reduced.(4)According to the refractive index of the oil at 930 nm wavelength,the optimal dispersion compensation coefficients of the above five oil products on the SD-OCT experimental platform are(13,12,15,14,10)a.u.,and the pulse broadening factors are 0.5155,0.5581,0.4107,0.5085,0.8793,respectively.This thesis contains the following three innovations.(1)In the current edible oil quality testing,the application of spectrometry to the construction of dispersion specificity index system for edible oils has not been reported,and in this study,the refractive index Cauchy coefficient matrix over a wide band of five oils was obtained using spectrometry as a unit of dispersion specificity index system for oil product identification.(2)Comparing with the refractive indices at narrow wavelengths or individual wavelengths studied by most institutions,this study used a high-precision and high-sensitivity spectrophotometer to obtain the refractive index functions of edible oils at a wide wavelength range from 380 to 1500 nm,and found that they have reliable normal dispersion rules,breaking through the limitations of current research results such as roughness and narrow wavelengths.(3)The OCT technology is used to study the tomographic image and dispersion of oil products,and the dispersion characteristics of oil products in OCT are extracted through the combination of deconvolution numerical dispersion compensation and experimental methods,and it is found that the best dispersion compensation coefficient and the corresponding pulse broadening factor are specific.This OCT application innovation has been affirmed by many SCI International Journal editors and reviewers.In conclusion,the refractive index variation characteristics of these five oils are relatively similar with wavelength,which reflects the existence of many correlation components for different oils;the analytical model of oil refractive index developed in the wider wavelength band from UV to IR is practically reliable;the numerical dispersion compensation of the performed oils can improve the axial resolution of OCT,and thus the optimal dispersion compensation coefficients and the corresponding pulse spreading factors for different oils are found The specificity of the dispersion compensation coefficients and the corresponding pulse spreading factors for different oils were found.Therefore,it is of great scientific value and application prospect to investigate the refractive index of oil products,and then explore the potential oil dispersion characteristics as a potential oil safety testing index.