Carmine is a widely used food pigment in various food and beverage additives. Excessive consumption of synthetic pigment shall do harm to body seriously. The food is generally associated with a variety of colors. Various pigments will interfere with each other, which increases the difficulty of detection of pigments in food. Under the simulation context of various food pigments' coexistence, we adopted the technology of fluorescence spectroscopy, together with the PSO-SVM algorithm, so as to establish a method for the determination of carmine content in mixed solution. Carmine and amaranth solid powders were purchased from reagent company. Carmine was selected as pigment to be detected, and amaranth was interfered pigment, carmine monochromatic solution with different concentrations and mixed solution after adding amaranth. The carmine concentrations of 0.1 similar to 30 mu g.mL(-1), interfered pigment amaranth concentrations of 0.1 similar to 10 mu g.mL(-1) were arbitrarily added. Using the FS920 steady state fluorescence spectrometer produced by Edinburgh Instruments Company, the fluorescence spectra of the carmine monochromatic solution and the mixed solution after the addition of amaranth were measured. The optimal excitation wavelength of carmine was lambda(ex) =326 nm. The optimal emission wavelength For lambda(em) =430 nm. The six different concentrations of monochromatic samples and mixed pigment samples were selected. Among them, the concentration of amaranth was set at 2 mu g.mL(-1), and the concentration of carmine was 3, 4, 5, 6, 7, 8 mu g.mL(-1) Observe the relationship between the emission spectra and the fluorescence intensity of the six samples at the excitation wavelength lambda(ex) =326 nm. In the monochromatic samples, the carmine concentration and fluorescence intensity were linear well. The fluorescence intensity of the six samples decreased first and then increased and then decreased again with the increase of the carmine concentration. It is proved that the fluorescence spectrum of the mixed solution is not simply superimposed by the spectrum of the components, but rather the competition and interaction between the carmine solution and amaranth solution in the process of absorbing the light spectrum. With 25 sets of carmine and amaranth mixed solution, seven of them were selected as prediction samples and the remaining 18 groups were used as training samples. The concentrations of carmine in the seven predicted samples were 1.0, 2.0, 4.0, 6.0, 9.0, 12 and 15 mu g.mL(-1), and the concentrations of the intercalating matter amaranth in the range of 0.1 similar to 10 mu g.mL(-1). The fluorescence intensities corresponding to the optimal excitation wavelength lambda(ex) = 326 nm of each sample were selected as the input of the detection model, and the predicted concentration of carmine was taken as the output. After initializing the PSO parameters, the optimal parameters c and g of SVM were trained. The optimal parameters were input into the PSO-SVM model. The predicted results of the seven predicted samples were: 1.1469, 1.8606, 3.8544, 6.1469, 9.1338, 11.8576, 14.8598 mu g.mL(-1). The results of PSO-SVM analysis showed that the average recovery of carmine was 100.84%, and the root mean square error of prediction (RMSEP) was 1.03x10(-4), and the correlation coefficient between model output and real value was 0.999. Under the same conditions, the concentrations of seven samples predicted BP method were 1.1401, 2. 1398, 3.1882, 6.4362, 8.8827, 11.8601 and 12.6643 mu g.mL(-1). The average recoveries was 98.56% The RMSEP was 4.65x10(-3) and the correlation between the output and the true value was 0.972. Compared with the predicted results of reverse transmission, the correlation coefficient of PSO-SVM was 2.7% higher, the average recovery rate for 0.6%, and the root mean square error was nearly one order of magnitude lower. According to the analysis results, it can effectively avoid the interference caused by pigment with the combination of the fluorescence spectrum technique and PSO-SVM, accurately determining the content of carmine in mixed solution with an effect better than that of BP.
