Towards Sensory Assessment Classification using Short-Wave NIR Spectroscopy for Orange Cultivars

Abstract The global orange industry constantly faces new technical challenges to meet consumer demands for quality fruits. Instead of traditional subjective fruit quality assessment methods, the interest in the horticulture industry has increased in objective, quantitative, and non-destructive assessment methods. Oranges have a thick peel which makes their non-destructive quality assessment challenging. This paper evaluates the potential of short-wave NIR spectroscopy and direct sweetness classification for Pakistani cultivars of orange i.e., Blood red, Mosambi, and Succari. The correlation between quality indices i.e., Brix, titratable acidity (TA), Brix: TA and BrimA (Brix minus acids), sensory assessment of the fruit, and short-wave NIR spectra is analyzed. Mix cultivar oranges are then classified as sweet, mixed, and acidic based on short-wave NIR spectra. Short-wave NIR spectral data was obtained using the industry standard F-750 fruit quality meter (310-1100 nm). Reference Brix and TA measurements were taken using standard destructive testing methods. Reference taste labels i.e., sweet, mix and acidic, were acquired by sensory evaluation of samples. For indirect fruit classification, partial least squares regression models were developed for Brix, TA, Brix:TA and BrimA estimation with a correlation coefficient of 0.57, 0.73, 0.66 and 0.55 respectively, on independent test data. For direct fruit classification, the ensemble classifier achieved 81.03% accuracy for 3 class (sweet, mix and acidic) classification on independent test data. We observed a good correlation between NIR spectra and sensory assessment instead of quality indices. Hence, direct classification is more suitable for orange sweetness classification using NIR spectroscopy than the estimation of quality indices.