Application of FT-NIR spectroscopy to assess the ripening stage of olives

In the olive sector, there is a growing interest in developing new analytical methodologies able to provide fast results directly in field. In this context, NIR spectroscopy can be a valid tool and the aim of this work was just the evaluation of its potential in monitoring the ripening stage of olives. In particular, preliminary results of a three-year research project granted by AGER, named “Sustainability of the Olive-Oil System - S.O.S.”, are here reported. The project involves six Italian Universities and it aims at improving the sustainability of the extra-virgin olive oil production chain. During the first year of the project, five cultivars of olives (Cima di Melfi, Oliva Rossa, Corsicana, Semidana, and Sivigliana) harvested at different stages during the ripening process were analyzed. In details, 1020 fruits were used to evaluate the maturity index based on visual inspection and to collect FT-NIR spectra (11000-3900 cm-1) by an optical fiber. After smoothing, a preliminary evaluation of the dataset by means of PCA revealed a sample distribution as a function of maturity index or origin/cultivar along PC1 and PC2, respectively. Pre-treated spectra (smoothing coupled with SNV or first derivative) were then used to calculate discriminant classification models (based on PLS-DA) able to correctly assign the olives to the four classes based on the maturity index. Good values of correct classification in prediction (external validation) were obtained with both the complete dataset (1020 spectra) and the subset containing only the 180 spectra of the cv. Cima di Melfi (84±6% e 83±8%, respectively). These results show the high potential of NIR spectroscopy in the evaluation of olive ripeness, paving the way for the development of customized portable devices to be used directly in field.