Relationships between fatty acid and sterol compositions and near infrared spectra of extra virgin olive oil samples from different geographical regions of Turkey

Extra virgin olive oil (EVOO) is known as the most healthy oil among other oil types. For this reason, consumers' interest in olive oil increases day by day. Determination of the quality of oil is important both for producers and consumers. The usage of Fourier transform near infrared spectroscopy (FT-NIR), which is faster and more environmentally friendly and uncomplicated against conventional methods of determining oil quality and sensory properties, is becoming more and more common. FT-NIR spectroscopy is able to connect to the production line therefore it offers online analysis capability, allowing you to advance the problems that may occur in the production line. Recent models obtained by combining chemometric methods with spectroscopic methods have shown great improvement in the quantitative analysis of olive oil. In the present study, FT-NIR spectra of 73 EVOO samples acquired from 21 different cultivars and 4 geographic regions were used to develop partial least square regression (PLS-R) models for the rapid quantification of sterols for the first time in the literature. The results of the verification model showed that the total sterol content of the EVOO samples could be predicted with good predictibility (Rp2=0.839, RMSEP=192 mg/kg, RPD=2.64). On the other hand, the prediction models for the individual sterol forms resulted ineffectually. Except for heptadecanoic and eicosenic acids, models with high predictibility could be established for the quantification of the major fatty acids found in EVOOs with Rp2 and RPD values ranging between 0.716-0.997 and 2.02-17.6, respectively. When fatty acids were grouped according to their unsaturation degree as SFA (Rp2=0.998, RMSEP=0.102%, RPD=21.8), MUFA (Rp2=0.997, RMSEP=0.255%, RPD=18.7) and PUFA (Rp2=0.998, RMSEP=0.147%, RPD=25.1), the obtained performances of the models were observed substantially higher than fatty acids separately. In conclusion, this study demonstrates that FT-NIR spectroscopy combined with chemometric analysis; it is a powerful analytical method by which olive oil producers can easily adapt olive oils to simple, rapid and simultaneous quantification of total sterols and fatty acid components.