Influence of the Peel on Predicting Soluble Solids Content of Navel Oranges Using Visible and Near-Infrared Spectroscopy

Abstract. The peel of orange was proven to influence light propagation within the fruit; thus, this study was aimed at investigating the influence of the peel on absorption spectra and calibration models within the wavelength range from 520 to 2200 nm. To investigate this effect further, the correlation between pulp soluble solids content (SSC) and peel SSC of the same oranges was studied. Spectra of 86 oranges with peel and peeled were collected using a commercial spectrometer, and partial least squares regression was used to develop calibration models. Results showed that for intact oranges, the calibration model using the visible and shortwave near-infrared (Vis-SWNIR) region (520-1100 nm) performed similarly to that using the Vis-NIR region (520-2200 nm), and the broader Vis-NIR region did not improve the calibration models. With respect to the influence of the peel, within the Vis-SWNIR and Vis-NIR regions, the models elaborated using peeled samples performed slightly better, but not significantly. In the NIR region, better results were obtained for models using intact samples. In addition, a linear correlation was found between pulp SSC and peel SSC, with a coefficient of determination (R²) of 0.5047, which could be used to explain why the peel did not have significantly negative influence on prediction performance. It was concluded that the peel of navel orange did not have significant influence on the SSC determination using Vis/NIR spectroscopy, and the .