Ripening assessment of ‘Ortanique’ (Citrus reticulata Blanco x Citrus sinensis (L) Osbeck) on tree by SW-NIR reflectance spectroscopy-based calibration models

The aim of this study was the non-destructive assessment ‘Ortanique’ (Citrus reticulata Blanco x Citrus sinensis (L) Osbeck) ripening, based on prediction internal quality attributes (IQA) by short-wave near-infrared reflectance spectroscopy (SW-NIRS) calibration models. Spectra from fruit 50 trees located in two different orchards, were acquired tree using a customized portable visible (vis-NIR) system. Partial least squares (PLS) used to build various IQA models tested through validation (IV) and external (EV). Generally, IV results always superior those EV: regarding IV, high regression coefficient (R2) low root mean square error (RMSEP) achieved, revealing good predictive performance for juice pH (R2 = 0.80; RMSEP 0.10; SDR 2.23), soluble solids content (SSC) 0.79; 0.75 %; 2.27), titratable acidity (TA) (R² 0.73; 0.24 % citric acid; 1.94) maturation index (MI) 1.38; 2.2). best EV predictions obtained TA 0.69; 0.38 1.24), MI 2.07; 1.49). Calibration glucose, fructose sucrose showed medium-coarse both strategies. A detailed investigation performed, understand causes their poor results. In context EV, model updating strategies explored some samples improve model. methods bias correction spiking tested, showing clear improvement predictions.