[Detection of Lead Chrome Green Illegally Added in Tea Based on Confocal Raman Spectroscopy].

In this paper, confocal Raman spectroscopy was applied to detect the contents of lead chrome green as a heavy-metal stain illegally added in tea. Firstly, Raman spectra of five different concentrations of lead chrome green in tea infusion were acquired based on specific concentration method. The qualitative analysis of sample added with lead chrome green was achieved with comparing the Raman spectra of sample and standard substance. Four main Raman characteristic wavenumbers, 1 341, 1 451, 1 527 and 1 593 cm(-1), were extracted for the qualitative identification of lead chrome green in tea. After spectral preprocessing of the raw Raman spectra, backward interval PLS (biPLS), competitive adaptive reweighted sampling (CARS) and successive projections algorithm (SPA) were combined to deeply mine the characteristic wavenumbers of lead chrome green in Raman spectra, and finally 14 characteristic wavenumbers were optimized. Partial least squares (PLS) and least square support vector machine (LS-SVM) were separately used to build the model based on the extracted 14 wavenumbers. As a result, these two models both had good robustness and high ability to predict and all the determination coefficient (R(2)) of calibration, validation and prediction were higher than 0.9, which proved the effectiveness of the extracted characteristic wavenumbers. Compared with the PLS model, the nonlinear model built by LS-SVM got a better result, R(2) of prediction was 0.964 and the root mean square error of prediction (RMSEP) was 0.535. This study indicated that it is feasible to detect the contents of lead chrome green illegally added in tea based on confocal Raman spectroscopy combined with specific sample treatment and chemometrics methods. This study helped the valid supervision of food safety problem on lead chrome green illegally added in tea.

[In Vivo Study of Chitin in Fungal Hyphae Based on Confocal Raman Microscopy].

Chitin is an important structural polysaccharide of fungal cell wall. In this paper, aerial hyphae of Colletotrichum camelliae Massee was first studied by confocal Raman microscopy in vivo. Firstly, the optimal experimental parameters of hyphae for collecting the Raman spectra were determined, and the typical Raman spectra of hyphae, chitin standard and background were acquired. By comparing analysis, characteristic peaks of chitin were found in hyphae. Then, a region of interesting on hyphae was selected for Raman scanning. Through principal component analysis, the Raman signal of hyphae and background in the scanning area can be separated clearly. Combined with loading weight plot, two main characteristic peaks of hyphae were obtained, 1 622 cm(-1) was belong to chitin and 1 368 cm(-1) was assigned to pectic polysaccharide. Finally, two and three dimension chemical images of fungal hyphae were realized based on Raman fingerprint spectra of chitin in a nondestructive way.

Nondestructive detection of lead chrome green in tea by Raman spectroscopy.

Raman spectroscopy was first adopted for rapid detecting a hazardous substance of lead chrome green in tea, which was illegally added to tea to disguise as high-quality. 160 samples of tea infusion with different concentrations of lead chrome green were prepared for Raman spectra acquirement in the range of 2804 cm(-1)-230 cm(-1) and the spectral intensities were calibrated with relative intensity standards. Then wavelet transformation (WT) was adopted to extract information in different time and frequency domains from Raman spectra, and the low-frequency approximation signal (ca4) was proved as the most important information for establishment of lead chrome green measurement model, and the corresponding partial least squares (PLS) regression model obtained good performance in prediction with Rp and RMSEP of 0.936 and 0.803, respectively. To further explore the important wavenumbers closely related to lead chrome green, successive projections algorithm (SPA) was proposed. Finally, 8 characteristic wavenumbers closely related to lead chrome green were obtained and a more convenient and fast model was also developed. These results proved the feasibility of Raman spectroscopy for nondestructive detection of lead chrome green in tea quality control.