Submitted to: International Symposium on Precision Agriculture
Publication Type: Proceedings
Publication Acceptance Date: 1/7/2008
Publication Date: N/A
Citation: Interpretive Summary: Olive fruit in individual bins that are brought into the processing plant often came from different growers and were harvested at different maturation stages with different levels of oil content, firmness and color. This quality variability in fresh olive fruit tends to produce inferior final products. For instance, unripe olives would cause problems in the fermentation process as these olives have poor skin permeability and low flesh to stone ratio. On the other hand, overripe olives tend to get soft quickly. Hence, there is a need to sort and grade olives in terms of inner and surface properties prior to processing to ensure high quality final products. In this research, Fourier transform near-infrared (FT-NIR) spectroscopy, which provides noninvasive, rapid measurement of light reflectance at individual wavelengths, was used to collect reflectance spectra from individual fresh olive fruit over the spectral range of 780-2500 nm. Color, firmness and oil content of the two varieties of olive fruit were then measured using standard destructive methods. Statistical models were developed relating nondestructive spectral measurements to the quality attributes of olives. Results showed a relatively good correlation between spectral measurements and fruit firmness with the coefficient of determination (or R**2) of 0.67. Somewhat lower correlation was obtained between spectral measurement and oil content (R**2=0.67). Excellent predictions of color were obtained with R**2 equal to or greater than 0.86. FT-NIR spectroscopy is potentially useful for nondestructive assessment of olive fruit. Development of an FT-NIR spectroscopy-based inspection system would greatly benefit growers and processors as well as consumers since the technique would ensure more consistent fresh olive fruit and thus better quality final products.
Technical Abstract: Quality features (firmness, oil content and color in terms of hue and chroma) of two olive (Olea europaea L) varieties (‘Ayvalik’ and ‘Gemlik’) were predicted using Fourier transform near-infrared (FT-NIR) spectroscopy. Reflectance measurements of intact olives were performed using a bifurcated fiber optic probe over the wavelengths of 780-2500 nm. Measurements of firmness, oil content and color values were made using standard methods, following the spectral measurements. Calibration models were developed using the partial least squares method for predicting the quality parameters of two olive varieties. Relatively good correlations were obtained for Magness-Taylor (MT) maximum force, which was used as a measure of firmness, for both ‘Ayvalik’ and ‘Gemlik’ varieties; the coefficient of determination (R**2) for ‘Gemlik’ olives was 0.67 (standard error of prediction or SEP = 1.37) in validation. Better oil content prediction of olive fruit was obtained for the pooled data of ‘Ayvalik’ and ‘Gemlik’ varieties with the R**2 value of 0.64 (SEP=0.05) in validation. Higher correlations were obtained for color predictions with R**2=0.88 and SEP=12.9 for chroma and R**2=0.86 and SEP=0.10 for hue for ‘Gemlik’. Similar color prediction results were obtained for the ‘Ayvalik’ variety. The research demonstrated the potential of using FT-NIR spectroscopy for nondestructive quality assessment of olives.