Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2006
Publication Date: 4/1/2007
Citation: Kavdir, I., Lu, R., Ariana, D., Ngouajio, M. 2007. Visible and near-infrared spectroscopy for nondestructive quality assessment of pickling cucumbers. Postharvest Biology and Technology. 44(2):165-174. Interpretive Summary: The quality of pickles or pickled products is directly related to that of pickling cucumbers. Increasing demands for better food quality from the consumer means that the pickle industry needs to inspect and grade pickling cucumbers and their green stocks more rigorously. Visible and near-infrared (Vis/NIR) spectroscopy is a technique that measures reflectance of light from the product item in the visible and near-infrared (longer than the visible) wavelength range; it has good potential in assessing the high moisture crops as it is fast, economical and, most importantly, nondestructive. Firmness, skin and flesh color, and dry matter content are important quality parameters for pickling cucumbers, and they directly influence the quality of pickles or pickled products. This research was aimed at developing a Vis/NIR spectroscopic method to assess quality attributes of pickling cucumbers. Two cultivars of pickling cucumbers were tested in the experiment over 18 days of cold storage. Vis/NIR measurements were found to correlate well with the firmness and skin and flesh color of the pickling cucumbers. Relatively good Vis/NIR measurements of dry matter content were also obtained for one cultivar of pickling cucumbers. Differences in quality measurements by the two spectroscopic instruments were observed, indicating the importance of selecting an appropriate instrument to meet measurement needs. Vis/NIR technique is useful for segregating inferior cucumbers from high quality cucumbers. The technique is promising for sorting and grading pickling cucumbers or their green stocks to ensure consistent, high quality pickles or pickled products.
Technical Abstract: This study was aimed at developing a nondestructive method for measuring the firmness, skin and flesh color, and dry matter content of pickling cucumbers by means of visible and near-infrared (Vis/NIR) spectroscopy. ‘Journey’ and ‘Vlaspik’ pickling cucumbers were hand harvested and then stored at 10°C and 95% relative humidity for various periods up to 18 days. Spectroscopic measurements were made from each intact cucumber in interactance mode with a low-cost CCD-based Vis/NIR spectrometer over 550-1100 nm and an InGaAs-based NIR spectrometer over 850-1650 nm. Standard methods were used to measure skin and flesh color, firmness, and dry matter content of the pickling cucumbers. Calibration models were developed using the partial least squares method for predicting firmness (i.e., maximum force, slope or area from the Magness-Taylor (MT) force/deformation curve), skin and flesh chroma and hue, and dry matter content. NIR measurements were correlated well with MT slope or area, with values for the coefficient of determination (R**2) of 0.70~0.73 for calibration and 0.67~0.70 for validation, better than those obtained with the Vis/NIR spectrometer. Vis/NIR measurements had good correlations with skin chroma (R**2=0.89 and 0.83 for calibration and validation, respectively) and hue (R**2=0.76 for calibration and validation); however, lower correlations were obtained for flesh color. The correlation between NIR measurements and skin and flesh color parameters was either low or insignificant. Promising results were obtained in predicting dry matter content of the Journey cucumbers with R**2=0.65 in validation. Pre-size sorting of the cucumbers prior to spectral analysis improved NIR prediction results for individual quality parameters. Visible and NIR spectroscopy is potentially useful for sorting and grading pickling cucumbers.