Non-destructive assessment of olive fruit ripening by portable near infrared spectroscopy

The feasibility of portable near infrared spectroscopy (NIR) technology for the determination of oil and moisture contents in intact olive fruits was studied. A total of 144 and 112 samples were collected throughout the ripening period in two different olive cultivar trials. Spectral data were recorded in the wavelength region from 1100 to 2300 nm at 1 nm intervals under two different experimental conditions: on-tree in the field in Trial 1 and under laboratory room conditions in Trial 2. Calibration models were developed and evaluated using partial least squares (PLS) regression separately for each trial set and for the combined group of samples. Although slightly better results were obtained under laboratory room conditions, the results obtained on-tree in the field were also accurate enough to determine the optimal harvest date of each cultivar. The combined model showed predictive statistics within the range of the individual models (r=0.89 and RMSECV= 1.99 for oil content and r=0.88 and RMSECV=2.06 for moisture content), which could be considered acceptable as an increase in the model robustness could be expected. These results encourage the use of portable NIR spectroscopy to monitor olive fruit ripening and to decide the optimal harvesting date on the basis of oil and moisture content.