Use of the hyperspectral imaging to estimate the volatile composition of Tempranillo grape berries during ripening

Volatile compounds present in grapes, and accumulated during the ripening process, are responsible for providing wine its main aromatic characteristics. However, there is currently no feasible and inexpensive method to monitor the volatile composition of grape berries during ripening. In recent years, hyperspectral imaging (HSI) has received wide recognition as a non-destructive and rapid technique for quality assessment in the agri-food industry. In this work, we have studied the use of HSI to estimate the volatile composition throughout ripening in berries of Vitis vinifera L. Tempranillo. For this purpose, 240 spectra in the visible-short wave near infrared (VIS+SW-NIR) range (400-1000 nm) were acquired from intact grapes in a laboratory. The reference method used was thin film solid phase microextraction - gas chromatography - mass spectrometry (TF-SPME-GCMS). Using this instrumental method, a total of 20 volatile compounds were quantified. Total soluble solids (TSS) were also determined and refractometry was used as the reference method. With the reference and spectral data, calibration model using modified partial least squares (MPLS) regression, and external prediction were built. Values of determination coefficient of cross validation (R2CV) >= 0.5 were obtained for all individual compounds except for alpha-terpineol, benzaldehyde, and (E)-2-hexen-1-ol. From these results, it can be affirmed that HSI in the VIS+SW-NIR range is an appropriate non-destructive tool to differentiate between high and low values of each volatile compound throughout the ripening of Tempranillo grape berries in a rapid and contactless way.