Monitoring carotenoids and derived compounds in grapes and port wines: impact on quality

Carotenoids were identified in Port wines where they have been shown to be precursors of norisoprenoids that have floral, fruity or sweet aromas. The finding that young Port wines contain significantly more carotenoids and chlorophyll-like compounds than old Port wines indicated that increases in norisoprenoids during ageing could be correlated with decreases of the aforementioned precursors. In subsequent simulated, forced-ageing experiments, lutein was more sensitive to temperature than β-carotene, and aged wines showed higher β-carotene/lutein ratios compared to young Ports. Norisoprenoid compounds that included β-damascenone, β-ionone, 2,2,6-trimethylcyclohexanone (TCH), 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN), and vitispirane were determined in 14 young and 45-year old (aged) Port wines. In a high oxygen environment, as is the case in Port wine, the levels of these compounds decreased while oxygen was being consumed. However, during barrel ageing, TDN, vitispirane and TCH levels increased significantly while β-ionone and β-damascenone levels decreased. During forced-ageing of Port wines, β-ionone and β-cyclocitral levels increased (2.5 times) in β-carotene-supplemented wines and model wines. Along with these compounds, levels of β-damascenone also increased in both lutein-supplemented wines and model wines. The role of carotenoids as biomarkers for Port wine quality lead to the development of non-invasive, non-destructive in vivo carotenoid quantitation strategies in grapes using vis-SWNIR (visible-short wave near infrared) spectroscopy techniques together with Process Analytical Technologies (PAT) methodologies to provide winemakers with state-of-the-art metabolic images of vineyards for precision winemaking.