Improving the phenolic composition of cv tempranillo wines by blending grapes of different ripening state

Polyphenols are present in a wide variety of plants and foods such as tea, cacao and grape1. An important sub-class of these compounds is the flavanols present in grapes and wines as monomers (e.g (+)-catechin or (-)-epicatechin), or polymers also called condensed tannins or proanthocyanidins. They have important antioxidant properties2 but their biosynthesis remains partly unknown. Some recent studies have focused on the role of glycosylated intermediates that are involved in the transport of the monomers and may serve as precursors in the polymerization mechanism3, 4. The global objective of this work is to identify flavanol glycosides in grapes or wines, describe their structure and determine their abundance during grape development and in wine.

Primary and secondary metabolites are major components of grape quality and wine typicity. Their accumulation is interconnected through a complex metabolic network, which is still not well understood. This study aims to investigate how the enzymes of central carbon metabolism interact with anthocyanin biosynthesis during grape berry development: does the accumulation of anthocyanins, which represents a non-negligible diversion of carbon metabolic fluxes, require reprogramming of central enzymes or is it controlled downstream of central metabolism? To this end, 23 enzymes involved in central carbon metabolism pathways have been analyzed in the berries of 3 grape cultivars, which have close genetic background but distinct temporal dynamics of anthocyanin accumulation.

Elemental sulfur is a fungicide used by grape growers to control the development of powdery mildew, caused by the fungus Erysiphe necator. This compound is effective, cheap and has a low toxicity with no withholding period recommended. However, high levels of S0 residues in the harvested grapes can lead to the formation of reductive sulfur compounds that can impart taints and faults to the wine. Hydrogen sulphide (H2S) is a very volatile and unpleasant sulfur compound which formation is connected to high residues of S0 in juice (10 – 100 mg/L).

Vineyard exposure to smoke can lead to grapes and wine which exhibit objectionable smoky and ashy aromas and flavours, more commonly known as ‘smoke taint’ [1, 2]. In the last decade, significant bushfires have occurred around the world, including near wine regions in Australia, Canada, South Africa and the USA, as a consequence of the warmer, drier conditions associated with climate change. Considerable research has subsequently been undertaken to determine the chemical, sensory and physiological consequences of grapevine exposure to smoke. The sensory attributes associated with smoke-tainted wine have been linked to the presence of several smoke-derived volatile phenols, such as guaiacols, syringols and cresols [2].

Vitis vinifera L. is the most widely cultivated Vitis species which includes numerous cultivars. Owing to their superior quality of grapes, these cultivars were long considered the only suitable for the production of fine wines. However, the lack of resistance genes in V. vinifera against major grapevine pathogens, requires for its cultivation frequent spraying with large amount of fungicides. Thus, the search for alternative and more sustainable methods to control the grapevine pathogens have brought the breeders to focus their attention on other Vitis species. In fact, wild Vitis genotypes present multiple resistance traits against pathogens, such as powdery mildew, downy mildew and phylloxera.