Oxidation vs reduction: the fate of tannins, pigments, vscs, color,SO₂ and metabolomic fingerprint

The Ibero-American Network of Viticulture, a component of the program of agricultural technology of the CYTED (Ibero-American Program of Science and Technology for Development), is developing the project “Zoning Methodology and Application in Viticultural Regions of Ibero-America”.

The ongoing climate change implies an increasing mean air temperature, which is signified by weather extremes or sudden changes between drought and local heavy rainfalls. These changing conditions are especially challenging for the established grapevine varieties growing under cool climate conditions due to an increased risk for fungal diseases like downy mildew (DM) and Botrytis bunch rot (BBR) as well as for grape sunburn. To meet that demand, the scope of most grapevine breeding programs is the selection of mildew fungus-resistant and climatic adapted grapevines with balanced, healthy yield and outstanding wine quality.

Oenological tannins are products extracted from various botanical sources, such as mimosa,
acacia, oak gall, quebracho, chestnut and tara. The polyphenolic component is obtained through a solid-liquid extraction also using specific solvents, then removed by evaporation or freeze-drying. Tannins are employed in two phases of winemaking, during the pre-fermentative phase or during fining with different purposes such as modulate antioxidant activity, colour stabilization, bacteriostatic activity, protein stabilization and modulation of sensory properties. To date, the current regulatory framework is not very clear. In fact, the Codex Alimentarius classifies commercial tannins as “food additives” but also as
“processing aids”. The main distinction is that “additives” have a technological function in the final food, whereas “processing aids” do not. In this sense, oenological tannins, despite the technological treatments, could contain aromatic compounds of the botanical species they belong to and release them to the wine.

Pulsed electric fields (pef) technology holds significant promise for the agrifood industry, considering the capacity of inducing cell electroporation, due to the disruption of cellular membranes. Pef-induced permeabilization is dependent of the chosen treatment protocol (i.e. Pulse shape, electrical field strength, specific energy) and of the matrix’s characteristics (i.e. Cell radii and size, ph, electrical conductivity).

Due to the central role of the ripening timing in the evaluation of the varietal response to the environmental resources, a method to manage maturation curves has been developed. The method produces an index of veraison precocity and overcomes several methodological problems, like the visual evaluation of the veraison point and the multi-annual and multi-varieties data processing. It is based on a statistical and mathematical processing of the sugar ripening curves.