Abstract: In this study, a line-scanning Raman hyperspectral imaging system was built to quantify sodium thiocyanate illegally added in skim milk powders with large sample areas. Firstly, the penetration depth of Raman signal produced by sodium thiocyanate in skim milk powders was measured. Then, ten milk powder mixtures with different concentrations of sodium thiocyanate were prepared and their hyperspectral images were also collected. The Gaussian filter smoothing and the airPLS baseline correction methods were used to preprocess the Raman spectra. The corrected images at 2 068.48 cm-1 waveband were extracted to determine the presence of sodium thiocyanate particles. The concentration and spatial distribution of the sodium thiocyanate particles were finally obtained using a simple binarization method. The results showed that the average Raman intensity of all the pixels in the region of interest increased linearly with the increase of sodium thiocyanate particles, and the determination coefficient was 0.991 5. In the binary images, the sum of all sodium thiocyanate pixels in the region of interest increased exponentially. The limit of detection (LOD) for sodium thiocyanate concentration was estimated as 0.01% without using any chemical reagents. This system could expand the area of milk powder samples to 80 mm × 80 mm at a time in a non-invasive and non-contact way. In our research, the sodium thiocyanate particles could be fast, non-destructively and extensively detected using the line-scanning Raman hyperspectral imaging system. Both the concentration and the spatial distribution of the sodium thiocyanate particles in skim milk powder could be acquired at the same time. This method has a great potential for practical application.

Key words: hyperspectral imaging, Raman spectroscopy, skim milk powder, sodium thiocyanate, line-scanning