Wine metabolome

1. Grape is the necessary raw material to produce wine. We could assume that grape contain an analogous number of metabolites with most the fresh fruits and vegetables. However, due to economical, cultural and historical issues, grapevines comprise a high biodiversity, since thousand of cultivars are known and cultivated around the world. Therefore, wine-makers often use more than one cultivar for the production of a wine, in order to combine their characteristics and thus the metabolites, and produce more complex and equilibrate final products. Usually the cultivars mixed have a very diverse sensorial profile, which can be explain by the diverse metabolic profile.
Examples of metabolites found in grapes: sugars (e.g. glucose and fructose), sugar alcohols (e.g. inositol), lipids, vitamins, amino acids, amines, bounded and free terpenoids or other volatiles/aromatic compounds, bound and free polyphenols (e.g. anthocyanins, flavanols, flavonols and stilbenoids), organic acids (e.g. tartaric acid) and several sulfur compounds.

2. The mandatory process for wine production is the alcoholic fermentation, by added or indigenous yeasts. However, this process is not limited to the production of ethanol from sugars. The known metabolism of yeast include several metabolites, belonging to the cycle of Krebs, the Ehrlich reaction, the liberation of several bounded metabolites, the fragmentation of big metabolites (e.g. lipids), the polymerization of others (tannins), catabolites of tryptophan ( serotonin and melatonin), sulfur compounds, etc. The presence of about 10% of ethanol help to make soluble (and maybe more bioavailable) several lipophilic metabolites, where in most of the other liquid foods are eliminated or partially removed as sediment.

3. For the production of many red wines the malolactic fermentation by bacteria follows the alcoholic one in order to stabilize the final product. The bacteria, next to the production of lactic acid from malic acid, consume also several other metabolites and deliver various new, enriching further the wine metabolome.

4. During winemaking, the oenologist uses several techniques in order to improve the quality of the final product. For example the microxygenation, which provoke thousands of changes to the metabolic profile of the wine, affecting the color stability and the texture of the wine (Arapitsas et al., Plos one, 2012).
A second important example is the addition of the the antimicrobial and antioxidant agent SO2. Due to its reactivity, SO2 has a great influence to the wine metabolic fingerprint and quality (Arapitsas et al., J Chrom A, 2014; Arapitsas et al. Scientific Reports, 2018; Roullier-Gall et al., Food Chemistry, 2017).
A third important practise is the use of wooden barrels. Wine, during its contact with the wood, is enriched with several metabolites extracted from the barrel, while various new metabolites are formed due to the introduction of the oxygen through the porous of the wood (Gougeon et al., PNAS, 2009).

5. Already the above four elements introduce many metabolites to the food called wine. But there is a final important player: time. Consumers prefer to eat and drink the majority of the foodstuff more fresh possible, and long storage is correlated with sensorial and nutritional value loss. Wine is one of the few foods where aging is positively correlated because the consumers know that the quality of several wines improves with the time. Many premium red wines (Barolo, Brunello di Montalcino, Amarone, Burgundy Pinot noir, Naoussa, Tannat, etc) are very aggressive when young, but with time/aging they getting smoother, they gain sensorial complexity and as result they increase their value. The sensorial changes occurring during aging are translated in thousands of reactions and metabolic variations (oxidations, reductions, metathesis, polymerizations, hydrolysis, etc) (Arapitsas et al. Metabolomics, 2014; Jeandet et al., PNAS, 2015; Arapitsas et al. Scientific Reports, 2018; Roullier-Gall et al., Food Chemistry, 2017 ).