Preliminary study on application of mid infrared spectroscopy for the evaluation of the virgin olive oil "freshness"

The freshness of extra virgin olive oils (EVOO) from typical cultivars of Garda regions was evaluated by attenuated total reflectance (ATR) and Fourier transform infrared (FT-IR) spectroscopy, in combination with multivariate analysis. The olive oil freshness decreased during storage mainly for oxidation process. In this research 91 extra virgin olive oils, packaged in glass bottles and stored at room temperature under light or in dark for different periods, were analysed, before and after storage, by both chemical methods and spectroscopic technique. Classification strategies investigated were Partial Least Square Discriminant Analysis (PLS-DA), Linear Discriminant Analysis (LDA), and Soft Independent Modelling of Class Analogy (SIMCA). The results show that ATR-MIR spectroscopy is a better technique than traditional chemical index in classifying olive oil samples stored in different conditions and thus in evaluating the freshness of olive oils. In fact the FT-IR PCA results allowed a better discrimination among fresh and oxidized oils, than samples separation obtained by PCA applied to chemical data. Then, the results obtained by the different classification techniques evidenced the ability of FT-IR spectra to discriminate among EVOOs stored in different conditions. Therefore spectroscopic technique could be applied for the prediction of EVOOs freshness proving information comparable to chemical modifications, being FT-IR spectroscopy results in agreement with classical methods results. The great advantages of this technique instead of chemical analysis are related to rapidity, non destructive characteristic and low cost per sample. So, ATR-MIR could represent a reliable, cheaper and faster classification tool able to verify the freshness of virgin olive oils (i.e the oxidative status).