**2.1 Spectra pre-treatment**

Prior to PCA, spectra were smoothed. Additionally, both spectra data sets were mean centred (MC) prior the analysis as a default procedure. In order to evaluate the effect of the standardization pre-treatment (1/Std) over the scores and loadings values, PCA was also conducted over the standardized spectra. Multivariate spectra analysis and data pre-treatment were carried out using The Unscrambler ® software version 9.8 from CAMO company.
