Measurement of qualitative parameters of grapes during the final stages of ripening using vis/NIR spectroscopy: application in real scale conditions in wineries

The present work had the aim of investigating the application of vis/NIR spectroscopy for the rapid measurement of grape main ripening parameters and of the polyphenol content during the final stages of the maturation process and at the winery consignment. This is the second experimental campaign carried out to validate the previously obtained results and the predictive models with further samples. The first campaign involved analyzes conducted in lab-scale conditions in the spectral range between 400 and 1650 nanometers on samples of grapes (Vitis Vinifera L.) variety "Ancellotta" at a distance of 150 mm between the sensor and the sample. During this second campaign, using the same instrument and respecting the conditions of the previous year, the acquisitions were conducted both in the laboratory and directly in the winery to verify the real feasibility and applicability of the technique. Partial Least Square (PLS) regression analysis was applied on grape spectra in order to predict different parameters such as Babo degrees and anthocyanins and polyphenol content. The results from the PLS models gave coefficients of determination and root mean square errors in calibration and in prediction, respectively, equal to 0.81 and 0.69, and 0.67 (mg/l) and 0.94 (mg/l) for Babo degrees, equal to 0.79 and 0.79, and 118.9 (mg/l) and 119.9 (mg/l) for anthocyanins, equal to 0.55 and 0.45, and 266.3 (mg/l) and 287.6 (mg/l) for polyphenols. Regarding anthocyanins and Babo degrees estimation, classification models (PLS-DA) have also been created, which are also very useful for evaluating the grape samples upon consignment. Vis/NIR technology has long been recognized as a green method that allows for considerable time savings: applying it in a sector with high added value, such as the wine one, to streamline and automate quality controls in cellars could help this industry to the leap in quality from an industry 4.0 point of view.