Detection For Additives Of Milk Powder Based On Raman Hyperspectral Imaging

Dairy products are a type of food produced from or containing the milk of mammals,primarily cattle,water buffaloes,goats and sheep.Dairy products include food items such as milk,milk powder,cheese,and butter.Proteins,fats,carbohydrates are abundant in dairy products which are the main nutrient sources in daily life.Currently,the need for dairy products is increasing constantly in China.However,people have lack confidence in the domestic brand dairy products,especially in the quality and safety of domestic brand dairy products.The technology for dairy products detecting is not efficient to monitor throughout the food chain of dairy products.Therefore,it is very important to research a new method which has characteristics of fast speed,reliability,nondestructive way,and suitable for large area samples.It can promote the development of China's dairy industry to restore confidence.It is of great significance to maintain food safety and ensure human health.In this paper,a line-scanning Raman hyperspectral imaging system was developed to detect milk powder for quality and safety.The optical characteristics of Raman signals in milk powder layer was investigated firstly.The system was used to detect milk powder samples mixed with additives or adulterants using the Raman hyperspectral images.In addition,the application of SORS technology in the detection of additives in dairy products was also explored.The main research contents and conclusions of the paper are as follows:?1?A line-scanning Raman hyperspectral imaging system was developed.The hardware part of the system includes excitation module,acquisition module and scanning platform.The operation of each function module was controlled by a software designed by LabView.The spectral correction of this system was used a pure polystyrene material.According to several group of experiments,the influences of several parameters were investigated,and the optimum parameters for milk powder sample were found.?2?The optical characteristics of Raman signals in milk powder layer was investigated.The optical properties of Raman signals produced by 5 different illegal additives in 3 types of milk powder were investigated by designing a two-layers sample.The experimental results show the characteristic bands of 5 kinds of illegal additives,such as sodium thiocyanate,melamine,dicyandiamide,ammonium sulfate and urea,appeared at 2068.48cm^-1,671.71cm^-1,2155.34cm^-1,971.59cm^-1 and 1004.92 cm^-1,respectively.With the increase of the thickness of milk powder layer,the Raman signal intensities of the additives were gradually attenuated,and the attenuation rate would decrease gradually.The attenuations of the Raman signal producted by same additive in the three types of milk powder layer were basically the same.Under this experimental conditions,the Raman signals produced by 5 kinds of illegal additives could all penetrate 5 mm thickness of milk powder layer.In order to guarantee a 100%penetrable proportion in each single-band image at characteristic waveband,the maximum depth of milk powder layer was 2 mm.It can be concluded that a sample with a 2 mm thickness is suitable for detecting additives in milk powder using Raman hyperspectral imaging system.?3?Simultaneous detection of various illegal additives in milk powder.Refer to the previous results,a designed aluminium alloy container was used to ensure the sample thickness at 2 mm during the scanning process.In the single-band images at 2068.48 cm^-1,671.71 cm^-1,2155.34 cm^-1,971.59 cm^-1 and 1004.92 cm^-1,the relationship between the average Raman intensity in the ROI and the additives?sodium thiocyanate,melamine,dicyandiamide,ammonium sulfate and urea?concentration was a linear relation respectively,which can be used to quantitative analysis the additives.The coefficients of determination in the 5 groups were reached 0.9742,0.9954,0.9949,0.9982 and 0.9892,respectively.Meanwhile,the total number of the additive pixels increases nonlinearly in binary images.The limit of detection for all additives concentration were estimated as 0.01%without using any chemical reagents.This system could expand the area of detect to 40 mm×80 mm for each time in a non–invasive and non-contact way.The research demonstrates that the Raman intensity in single-band corrected image can be used for quantitative analysis of the corresponding additives,and the binary images can reveal the identification and the distribution of multiple additives simultaneously in skim milk powder.?4?Study on identification of milk powder authenticity.The line-scanning Raman hyperspectral imaging system was used to detect the starch and sucrose adulterated in milk powder.According to the Raman hyperspectral images,the characteristic bands of starch and sucrose adulteration were at 474.88 cm^-1 and 844.16 cm^-1,respectively.The linear relationship between the intensity of the pixels in the single band image and the concentration of the adulteration was good,and the coefficients of determination in each model could reach 0.9980 and 0.9985,respectively.The limit of detection for both adulteration concentration were estimated as 1%without using any chemical reagents.In the heap maps,the concentration of the adulterants in different areas and the density of the particles can be visualized.?5?Study of dairy product safety detection based on SORS.A point source was replaced the original line laser in Raman hyperspectral imaging system.The illegal additives in different dairy products were detected using new system,and the Raman spectra obtained at different offset points were contrasted and analyzed.The results show that the intensity of the Raman signal would decrease gradually as the offset point was farther away from the excitation point.The signal attenuation of different substances was basically the same,and the optimum distances of the offset point were less than 10 mm.In the results of two-layers samples,the intensitis of the Raman signal collected at the same offset point were different when the thickness of the top or bottom layer is changed,respectively.In the results of dairy product samples,the SORS ratio increased gradually as the offset position was removed from the excitation point.The attenuation of Raman signals produced by bottom layer was lower than that of top layer.The spectral information of deeper samples can be obtained by this method.