Application of Visible/Near-Infrared Spectroscopy Combined with Machine Vision Technique to Evaluate the Ripeness of Melons (Cucumis melo L.)

Visible/near-infrared (Vis/NIR) spectroscopy was applied to determine the ripeness of melons (Cucumis melo L.). The total soluble solids (TSS) and flesh color distribution around the equator fracture surface was studied, and a high correlation between TSS and flesh color in the outer mesocarp region was observed. A new ripeness index, defined as the edible ratio (ER), was proposed. One hundred and twenty melons with similar sizes were selected as samples and divided into a calibration set and a prediction set. Spectra of melons were acquired separately under transmittance and interactance modes. A machine vision system was established to acquire images of the melon fracture surfaces to further calculate the ER values of the melons. Partial least squares (PLS) calibration models were developed to predict the melon ripeness indices, including TSS, surface color (SC), and ER value. The results were promising for TSS, Hunter a, and ER value. For Hunter b, the results were insufficient. In addition, by comparing the performances of the calibration models developed under different detection modes, it was concluded that the best calibration results for TSS and ER were achieved under the transmittance mode, while for Hunter a, the best result was obtained using interactance spectra.