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

Background A field experiment was conducted to test the reliability of the near infrared spectroscopy (NIR)acousto-optically tunable filter (AOTF) 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 the partial least squares model carried out for the cultivar Arbequina', the coefficient of determination in calibration (R2c) was 0.991, while the coefficient of determination in cross-validation (R2cv) was 0.979. For the cultivar Frantoio' the indexes were 0.982 and 0.971, respectively; while for the cultivar Leccino' R2c was 0.977 and R2cv was 0.965. Finally, for the combined model (sum of the three varieties) these indexes were 0.921 and 0.903, respectively. The residual predictive deviation (RPD) ratio was insufficient for the predictive model of cultivar Leccino' only (1.98), whereas in the other cases the RPD ratios were completely sufficient, within the estimation range over 2.53 (2.61 in the global model, and 4.23 in the cultivar Frantoio'), or in describing a large capacity with values greater than 5, as in the cultivar Arbequina' (9.58). Conclusion NIR-AOTF spectroscopy proved to be a novel, rapid and 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 up new scenarios for determining the optimal time for harvesting olive trees to obtain maximum oil production. (C) 2012 Society of Chemical Industry