Other Metabolisms with Sensorial Impact

Methionine metabolism Sulfur compounds, responsible for aroma in wine and typically related to the grape variety, are released by yeast during the AF. In addition, the metabolism of the sulfur-containing amino acid methionine has an impact on wine aroma. Lact. brevis, Lact. plantarum, and O. oeni strains, using a pathway similar to dairy LAB, catabolize methionine producing light volatile sulfur molecules such as methanethiol and dimethyldisulfide, and heavy volatile molecules such as 3-(methylsulphanyl) propan-l-ol and 3-(methylsulphanyl) propionic acid (Pripis-Nicolau et al. 2004 Weimer et al. 1999 VaUet et al. 2008). In wine, O. oeni strains produce more heavy compounds, mainly 3-(methylsulphanyl) propionic acid, than lactobacilli. In water 3-(methyl-sulphanyl) propionic acid descriptors are chocolate and roasted but these notes are not found in wine where they are replaced by red fruit and earthy odors probably because of interactions with other wine components (Pripis-Nicolau et al. 2004). 

Synthesis and hydrolysis of esters Sensorial and chemical analyses of more than 60 volatile compounds showed that during MLF of red wines the main character affected was the fruity note, which is related to fatty acid ethyl esters (Antalick et al. 2012). LAB are able to modify these compounds as they may degrade or synthesize them from fatty acids (Costello et al. 2013), with the concomitant reduction or intensification of the fruity note (Sumby et al. 2013). Actually, the phenomena underlying the variability of the impact of MLF on the fruity note of red wines are more complex than a simple strain effect. These variations reflect a bacteria-yeast-wine triptych in which each component is irr5)ortant. It is illusory to presume that a given aromatic impact can be ensured by the use of a particular bacterial strain (Antalick et al. 2012). 

The bitterness disease The excessive bitterness of wine, described at the very beginning of wine microbiology, results from the glycerol metabolism, an abundant component of wine (7 to 10 g/1). In winemaking, degradation of glycerol is detrimental due its bad impact on taste. Several LAB 

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