Oil accumulation in intact olive fruits measured by near infrared spectroscopy-acousto-optically tunable filter

A field experiment was conducted to test the reliability of the near infrared spectroscopy (NIR) method to measure mesocarp oil content in vivo against nuclear magnetic resonance (NMR) determinations using three different olive cultivars at different stages of ripening. RESULTS: In PLS model carried out for the cultivar Arbequina the R2c (coefficients of determination in calibration) obtained was of 0.991, while the R2cv (coefficients of determination in cross-validation) of 0.979; for the cultivar Frantoio the indexes were respectively of 0.982 and 0.971, for the cultivar Leccino of 0.977 for R2c and 0.965 for R2cv. Finally, for the combined model (sum of the three varieties) those indexes were respectively equal to 0.921 and 0.903. The RPD ratio was insufficient for predictive model of cultivar Leccino only (1.98), whereas in other cases RPD ratios were completely sufficient, within the estimation range over 2.5 - 3 (2.61 in global model, and 4.23 in cultivar Frantoio), or describing a great capacity with values greater than 5 as in the case of the cultivar Arbequina (9.58). CONCLUSION: The NIR proved a novel, rapid, reliable method to monitor the oil accumulation process in intact olive fruits in the field. The innovative approach of coupling NIR and NMR technologies opens new scenarios for determining the optimal time for harvesting olive trees to obtain maximum oil production.