**2.3.2 PCA-loadings**

Fig. 5 (a) depicts six representative fluorescence spectra corresponding to each type of mezcal analysed. A high similarity between the fluorescence spectrum of ethanol and white/young mezcal is observed. On the other hand, rested, abocado and distilled mezcals, have similar spectra. Finally, the huge differences between the intensity of the emission spectra corresponding to aged mezcal, and that of the other types of mezcal, can be attributed to the higher concentration of organic molecules coming from the wood cask during the maturation process.

This also explains the grouping along PC1-axis. From these results, it can be concluded that PC1 can discriminate between naturally/artificially matured samples and white mezcal samples. On the contrary, the one-dimensional PC1-loading plot obtained from standardized spectra; does not provide clear information about the objects distribution.

In this sense, and according with the results described above, the standardization pretreatment does not improve the discrimination between samples in the scores plots. On the contrary, it leads to a misinterpretation of the loading plots.

Fig. 5. (a) Representative raw fluorescence spectra for each type of mezcals, (b) PC1-loadings plot for the centred spectra, and (c) PC1-loadings plot for standardized spectra.
