Fluorescence spectroscopy and chemometric techniques for geographical discrimination of green tea samples

The geographical origin of tea samples is an important factor to determine quality and reputation of a commercial tea product. Recently, different analytical procedures have been proposed for classification of different varieties or geographical origin of teas, including HPLC, elemental analysis, UV–vis spectroscopy, Near-Infrared spectroscopy, electronic tongue, electronic nose, multispectral or hyperspectral imaging, HPLC-DAD-MS. In our previous study, the content of catechins and methylxanthines in 92 green tea (GT) samples originating from China and Japan was determined by using micellar electrokinetic chromatography, and pattern recognition methods were applied to discriminate GT samples according to geographical origin. In this study, an alternative analytical approach for the geographical discrimination of the GT samples is proposed, based on the combination of excitation–emission matrix (EEM) fluorescence spectroscopy as analytical technique and chemometric tools. Excitation-emission spectra were recorded using a Perkin–Elmer LS 55 (Perkin-Elmer Ltd., Beaconsfield, UK) luminescence spectrometer, with excitation and emission slits both set at 10 nm. Emission spectra were recorded between 295 and 800 nm, at excitation wavelength ranging from 200 to 290 nm. Principal Component Analysis was used as a display method, and considering the 3-way data sets (samples, excitation and emission wavelengths) PARAFAC was applied as a multi-way decomposition method in order to extract the useful information from the spectra. The classification results obtained by EEM fluorescence spectroscopy were compared with those previously obtained by using micellar electrokinetic chromatography, finding a good agreement and thus demonstrating that fluorescence spectroscopy can be considered as a promising method for classifying GT by its origin.