Visualization of Thiourea in Bulk Milk Powder Based on Portable Raman Hyperspectral Imaging Technology On-Site Rapid Detection Method
Research
YANG Qiao-ling1, 2, CHEN Qin2, NIU Bing2, DENG Xiao-jun3*, MA Jin-ge3, GU Shu-qing3, YU Yong-ai4, GUO De-hua3, ZHANG Feng5
1. School of Environmental and Chemical Engineering，Shanghai University，Shanghai 200444，China
2. School of Life Sciences，Shanghai University，Shanghai 200444，China
3. Technical Center for Animal Plant and Food Inspection and Quarantine, Shanghai Customs, Shanghai 200135, China
4. Shanghai Oceanhood Opto-Electronics Tech. Co., Ltd., Shanghai 201201, China
5. Chinese Academy of Inspection and Quarantine, Beijing 100176, China
Abstract：Thiourea is a potential protein adulteration compound with high nitrogen content and high toxicity. Conventional laboratory testing methods are complicated in-process and low inefficiency and cannot meet the port’s demand for rapid quality screening of large batches of bulk milk powder samples. In order to solve the problem of the lack of rapid real-time evaluation methods for port sampling supervision, this research uses a self-built portable point scanning Raman hyperspectral imaging system to develop a simple and efficient on-site visualized rapid detection method of thiourea in milk powder to ensure accurate supervision of bulk milk powder in the import and export process. In the study, thiourea milk powder mixtures with different additive concentrations (0.005%~2.000%) were used as samples. Whittaker smoothing method and adaptive iteratively reweighted penalized least squares (airPLS) were used to eliminate random background noise signal and fluorescent background interference of spectral data.. After peak identification, the single-band data at the characteristic displacement of thiourea is binarized to obtain a binary heat map of the region of interest of the mixed sample. The qualitative identification and positioning analysis of thiourea in milk powder can be carried out through the presence or absence and coordinates of the thiourea pixel in the binary map. Further analysis of the relationship between the number of thiourea pixels in the region of interest and the concentration of addition showed that with the increase of the concentration of addition, the number of thiourea pixels increased linearly, and the coefficient of determination (R2) of linear fitting was 0.991 3, the lowest detectable concentration of thiourea is 0.05%. Under the addition levels of 0.25%, 0.60%, 1.20%, and 1.50%, the number of pixels and the linear fitting relationship is used to predict the concentration of thiourea in milk powder. The results show that the relative error range of the predicted concentration is -9.41%~4.01%, the relative standard deviation is less than 7%. The point scanning Raman hyperspectral imaging system can complete the detection of a single sample within 10 minutes, combined with the software control system, real-time qualitative, quantitative and pollution distribution analysis of thiourea particles in milk powder. The method has the advantages of being simple and efficient, high sensitivity and stability, and good accuracy. It provides a technical supervision method for the real-time and rapid detection of adulterated thiourea in bulk milk powder at the port site and can significantly improve the quality evaluation of the supervision link of the bulk sample at the port, provide technical support for the rapid customs clearance of imported milk powder.
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