Non-Invasive Measurements of the Internal Quality of Intact 'Gannan' Navel Orange by VIS/NIR Spectroscopy

Abstract

Visible and near-infrared (VIS/NIR) spectroscopy has become a popular technique for non-invasive quality assessment of intact fruits. This work presents an application of a low-cost, commercially available NIR spectrometer for estimation of soluble solids content (SSC), titratable acidity (TA), and available acidity (pH) of 'Gannan' navel oranges (Citrus reticulata cv. orange). VIS/NIR spectra were acquired using a custom-designed, contact optical-fiber probe, and were recorded in transmission mode. Calibration models relating the VIS/NIR spectra to SSC, TA, and pH were developed based on two different regression methods, partial least square (PLS) regression and principal component regression (PCR), with respect to percent transmission (%T) spectra data and first- and second-derivative spectra. The prediction performance of the calibration models in different wavelength regions was also investigated. The best models were based on PLS regression methods, with root mean standard errors of validation (RMSEP) of 0.464 °Brix, 0.704 g L-1, and 0.125, and correlation coefficients (r2) of 0.804, 0.643, and 0.651 for SSC, TA, and pH, respectively. Based on the results, it can be concluded that VIS/NIR spectroscopy could be a reliable, accurate, and fast method for non-invasive measurements of navel orange SSC and acidity.