Relationship between the bulk optical properties and the quality properties of citrus fruit

C.J. Sun, R. Van Beers, B. Aernouts, W. Saeys
Total soluble solids content (TSS) and titratable acidity (TA) are two important parameters in the quality evaluation of citrus fruit. Series of models based on optical techniques have been built for the estimation of these two parameters. However, the robustness of these models still needs to be improved. Therefore, the aim of this study was to investigate the relationship between the bulk optical properties (BOP) and TSS, TA of citrus fruits. Four species of citrus fruit (grapefruit, orange, lemon and lime) and 2 different sizes for each species (diameter difference is around 5-12 mm) were studied, resulting in a total of 56 samples. The BOP of juice and sacs were measured with a double integrating spheres (DIS) and unscattered transmittance setup in the range of 500-1400 nm. The values of TSS and TA were respectively obtained with a refractometer and potentiometric titration method. Then, partial least square regression (PLSR) was used to predict TSS and TA for juice and sacs from the absorption (µa), scattering (µs) and extinction (µt) coefficient spectra. All the models for sacs outperformed the corresponding ones for juice. For TSS detection, the model performance based on µa was worse than the others and the best model was achieved based on µt (R2CV=0.795, RMSECV=1.159). For TA detection, the model based on µa provided the best results (R2CV=0.875, RMSECV=0.947). All the results indicated the feasibility of using BOP for the prediction of TSS and TA in citrus fruit and gave a better understanding how the TSS and TA are related to the spectra, providing useful information for further model application and the design of spectral-based setups for quality monitoring on citrus fruit.
Sun, C.J., Van Beers, R., Aernouts, B. and Saeys, W. (2021). Relationship between the bulk optical properties and the quality properties of citrus fruit. Acta Hortic. 1311, 39-46
DOI: 10.17660/ActaHortic.2021.1311.5
total soluble solids, titratable acidity, bulk optical properties, citrus fruit, double integrating spheres

Acta Horticulturae