Polyphenolic compounds in Sauvignon Blanc - from grapes to wine

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At harvest, the metabolic composition of wine grapes reflects the accumulated effect of the environmental conditions, the stresses endured, and viticultural manipulations applied during the growing season. The role of the winemaker is to extract and nurture this “metabolite potential” throughout the winemaking process. However, it is typically difficult to relate this grape potential to that of the eventual wines. In this study, a holistic view of Sauvignon Blanc grape and wine polyphenolic compounds was attempted by measuring these compounds from different matrices, from ripe grape tissues up to the final wine, including the submatrices, such as juice, pomace and sediment. Sauvignon Blanc vines from one vineyard block were manipulated to yield berries with distinctly different phenolic potentials by creating a high light (HL) or a low light (LL) microclimate in the fruiting zone of the canopy during the growing season. The analyses of the HL and LL berries and wines, as well as concomitant analyses of the phenolic compounds in the submatrices, allowed their tracing as they were (i) transferred from one matrix to another, (ii) lost as waste products, or (iii) affected by different winemaking practices (skin contact and/or fermentation in contact with the juice sediment) implemented in the experimental design. In berries, flavonols showed the largest increase due to sun exposure (HL treatment) but were absent from the juice samples at all juice processing stages. They were however detected in the juice sediment, together with high concentrations of organic acids and sugars. Juice processing was noted for dramatic fluctuations in metabolite concentrations suggesting intense metabolic activity in this pre-fermentation matrix. Both skin contact and sediment contact treatments delivered wines with higher concentrations of coutaric acid (the ester formed from coumaric and tartaric acid) and the flavanol catechin while epicatechin concentrations was unaffected. The higher catechin concentrations did not lead to increased perceived bitterness in the wines, except in the sediment contact treatments. The total phenolic compound concentration of wine from LL (low phenolic potential) grapes was comparable to wine from HL (high phenolic potential) grapes, when skin contact, or sediment contact treatments were employed. From a sensory perspective, the sediment contact decreased the fruity aromas of Sauvignon Blanc, while the skin contact treatment enhanced the sensorial properties of the wines made from the LL grapes, allowing increased extraction from the skin-accumulated impact compounds.