Assessment of Tomato Quality Using Portable NIR Spectroscopy and PLSR with Wavelengths Selection

The evaluation of physico-chemical quality of tomatoes is time consuming and expensive because it requires operators and the consumption of chemicals. In this way, the development of a non-destructive and rapid method to assess the fruit quality would be suitable. The present study aimed at developing a portable NIR spectroscopic method to determine the soluble solids content, firmness and colour of tomatoes without the fruit destruction. NIR spectra (690-1700 nm) were directly acquired on the whole fruit using a portable NIR spectrometer. Spectral acquisition was carried out by placing the fruit directly in front of the spectrometer opening situated at the end of the pistol. For each fruit, NIR measurements were done on the 4 quarter of the fruit along the equator of the tomato. Then, firmness of tomato was measured using a durofel device while the background of skin colour was characterized by spectro-colorimetry. Immediately after firmness measurement, each fruit was mixed using a juice centrifuge and the obtained juice was filtered using a filter paper. Soluble solids content of filtered juice was determined by refractometric method. PLS regressions with leave-one-out procedures were carried out to perform linear models of prediction between spectral data and the values obtained from the physico-chemical analyses. The accuracy of the predictions was discussed according to the correlation coefficient value (R), the root mean square error of calibration/cross-validation (RMSEC/CV). The obtained results showed a good precision concerning the determination of soluble solids content with a RMSECV lower than 0.4% Brix. Concerning firmness, the determination remained correct with a RMSECV of 5.9 DI for a range of firmness values comprised between 51 and 100 DI. Finally, the determination of the tomato skin colour was correct for L* parameter with a RMSECV of 2.26 and quite imprecise for a* parameter with RMSECV of 3.02.