Looking for the optimal harvest time of red grapes with an enzymatic electrochemical multisensory system

The timing of the grape harvest is a critical decision for winemakers, as it greatly impacts the quality and organoleptic characteristics of the resulting red wines. One key indicator for determining the optimal harvest time is the phenolic content of the grapes. As the berries ripen, phenolic compounds in the grape skin cells migrate from the seeds to the pulp and finally to the skin. However, monitoring these phenolic changes, particularly in the seeds, presents a challenge. This research addresses this problem by developing a novel technique to track the phenolic composition of seeds during ripening. The objective is to provide a reliable method for winemakers to monitor the phenolic evolution and improve harvest decision-making. In this study, a multisensory system consisting of four electrochemical enzymatic carbon paste sensors, modified with tyrosinase and electrocatalytic materials (AuNPs, lutetium phthalocyanine, and nickel oxide nanoparticles), was employed to analyze the phenolic content in grape seed extracts. The system monitored weekly changes in the phenolic composition of the seeds from three red grape varieties—Cabernet Sauvignon, Tempranillo, and Prieto Picudo—during their ripening from veraison to being overripe. Using voltammetric techniques, the electrochemical responses were characterized by shifts in peak positions and intensity changes, reflecting the oxidation/reduction of phenols. Principal Component Analysis (PCA) demonstrated the ability of the array of sensors to discriminate phenolic changes across ripening stages, while Partial Least Squares (PLS) regression provided robust correlation models between the electrochemical responses and seed phenolic content, with correlation coefficients ranging from 0.93 to 0.99. The developed methodology successfully tracked phenolic changes, offering a promising tool for monitoring grape seed maturation and assisting in determining the optimal harvest time. • Enzymatic electrochemical CPE modified with electrocatalytic materials have been developed. • Seed extracts of different red grapes have been analysed during ripening using voltammetry. • Phenolic maturation can be monitored from the voltammetric responses. • Excellent PLS correlations were found with TPI and Folin-C. Indexes.