Abstract
The aim of this study was the non-destructive assessment of ‘Ortanique’ (Citrus reticulata Blanco x Citrus sinensis (L) Osbeck) ripening, based on the prediction of internal quality attributes (IQA) by short-wave near-infrared reflectance spectroscopy (SW-NIRS) calibration models. Spectra from fruit of 50 trees located in two different orchards, were acquired on tree using a customized portable visible near-infrared (vis-NIR) system. Partial least squares (PLS) was used to build the various IQA calibration models. The models were tested through internal validation (IV) and external validation (EV). Generally, the IV results were always superior to those of EV: regarding IV, a high regression coefficient (R2) and low root mean square error of prediction (RMSEP) were achieved, revealing a good predictive performance for juice pH (R2 = 0.80; RMSEP = 0.10; SDR = 2.23), soluble solids content (SSC) (R2 = 0.79; RMSEP = 0.75 %; SDR = 2.27), titratable acidity (TA) (R² = 0.73; RMSEP = 0.24 % citric acid; SDR = 1.94) and the maturation index (MI) (R2 = 0.80; RMSEP = 1.38; SDR = 2.2). The best EV predictions were obtained for TA (R2 = 0.69; RMSEP = 0.38 % citric acid; SDR = 1.24), and MI (R2 = 0.69; RMSEP = 2.07; SDR = 1.49). Calibration models for glucose, fructose and sucrose showed medium-coarse predictions for both validation strategies. A detailed investigation of MI models was performed, to understand the causes of their poor EV results. In the context of EV, model updating strategies were explored by using some validation samples to improve the calibration model. The methods of bias correction and spiking were tested, showing a clear improvement in the predictions.
Highlights
The aim of this study was the non-destructive assessment of ‘Ortanique’ (Citrus reticulata Blanco x Citrus sinensis (L) Osbeck) ripening, based on the prediction of internal quality attributes (IQA) by short-wave near-infrared reflectance spectroscopy (SW-NIRS) calibration models
The orchard influenced differently the IQA levels, and the content of the various biochemical analytes measured in the ‘Ortanique’ juice sampled, this was dependent on the sampling time/date (Table S1)
This study demonstrates the strong potential for the use of SW-NIRS as a smart tool to provide an extensive, fast, and real-time assessment of the ripeness of ‘Ortanique’ citrus fruit on tree
Summary
The aim of this study was the non-destructive assessment of ‘Ortanique’ (Citrus reticulata Blanco x Citrus sinensis (L) Osbeck) ripening, based on the prediction of internal quality attributes (IQA) by short-wave near-infrared reflectance spectroscopy (SW-NIRS) calibration models. Despite the availability of portable spectrometers, only a few studies have focused on their capacity to assess the IQA of oranges and mandarins on tree, perhaps due to the complexities involved and the performance deterioration of calibration models Those reported, pre sent in general, models with a moderate predictive performance for the various IQA, namely SSC in five cultivars of sweet orange from Cali fornia (Zude et al, 2008), pericarp thickness, SSC, MI, TA and BrimA in ‘Clemenvilla’ mandarin and ‘Powell Navel’ orange (Sanchez et al, 2013a; Torres et al, 2017, 2019), SSC and maximum penetration force in ‘Powell Summer’ orange (Sanchez et al, 2013b), SSC, MI and juice pH in ‘Newhall’ orange (Cavaco et al, 2018), and for SSC, chlorophyll and sugar content of several citrus cultivars (Stivastava and Sadistap, 2018)
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