Metabolomics for grape and wine research: exploring the contributions of amino acids to wine flavour

It is a well-established fact that premature oxidation is noxious for wine aromatic quality and longevity. Although some oxidation-related aroma molecules have been previously identified, there are not works carrying out systematic research about the changes in the profiles of odour-active volatiles during wine oxidation.

Wine lees are quantitatively the second most important wine by-product after grape stems and marc [1]. In order to recycle, distilleries recovered ethanol and tartaric acid contained in wine lees but yeast biomass is often unused. It has already been demonstrated that this yeast biomass could be upcycled to produce yeast extracts of interest for wine chemical stabilization [2]. In addition, it is well known that lees, during aging, release compounds that preserve wine from oxidation.

The pre-fermentative steps play a relevant role for the characteristics of white wine [1]. In particular, the grape pressing can affect the chemical composition and sensory profile and its optimized management leads to the desired extraction of aromas and their precursors, and phenols resulting in a balanced wine [2-4]. These aspects are important especially for must addressed to the sparkling wine as appropriate extraction of phenols is expected being dependent to grape composition, as well.

Mousy off-flavor is one of the defects of microbial origin in wine. It is described as a particularly unpleasant defect reminiscent of rodent urine (a “dirty mouse cage”), and grilled foods such as popcorn, rice, crackers, and bread crust. Prior to the 2010s, mousiness was very uncommon but it has been becoming more frequent in recent years. It is often associated with an increase in pH as well as certain oenological practices, which tend to significantly decrease the use of sulfur dioxide.

Climate change is leading to an increase in average temperature and in the severity and occurrence of heatwaves, and is already disrupting grapevine phenology. In Australia, with the evolution of the weather of grape growing regions that are already warm and hot, berry composition including flavonoids, for which biosynthesis depends on bunch microclimate, are expected to be impacted [1]. These compounds, such as anthocyanins and tannins, contribute substantially to grape and wine quality. The goal of this research was to determine how flavonoid extraction is impacted when bunches are exposed to high (>35 °C) and extreme high (>45 °C) temperatures during berry development and maturity.