Validation of a commercial optoelectronics device for grape quality analysis

In modern viticulture, grape quality monitoring and management during ripening plays a key role in the winemaking process. Conventional monitoring techniques are based on in-field refractometer measurement and eventually determination of acidity by titration, which are time-consuming tasks. Despite proximal and remote sensing may be used to estimate grape maturity in a relatively short time, the determination of the number of specific chemical components that change during the maturation process, such as malic acid and tartaric acid, may be not accurate. Smart chemometric techniques represent promising technologies for grape quality monitoring, allowing accurate grape chemical components determination in a short time. In the present study, a novel optoelectronic device for colorimetric and enzymatic analysis is presented: it relies on implementation of a LED light source with a wavelength emission ranging between 340 nm and 760 nm, a cuvette housing containing berry juice, and a photodiode. The device was applied for the determination of grape components involved in the maturation process: ten sampling plots of 20 plants each were selected in a 9-hectare experimental vineyard (Vitis vinifera cv. Glera trained as Sylvoz). The maturation development was monitored by collecting 250 berries from each sampling plot at 3 different times, from veraison until harvesting. Berries juice was analyzed using the optoelectronic device along with the conventional methodology. Absorbance measurements were used in order to determine the grape concentration of dissolved sugar, malic acid, and tartaric acid. In addition, the device was implemented to determine the pH and titratable acidity of the grape sample. Preliminary results gave evidence of an RMSE of 0.119 and 1.027 and an R2 of 0.94 and 0.98 for pH and titrable acidity respectively, suggesting an effective use of the optoelectronic device for grape quality monitoring. The final paper will include dissolved sugar content, malic acid, and tartaric acid validation using HPLC methodology.