Ethyl-phenol from yeast

Ethyl phenols are a result of enzymatic activities linked to the decarboxylation of cinnamic acids and the subsequent reduction in vinyl phenols caused by the Brettanomyces/Dekkera yeast genus (Chatonnet et al., 1992), apart from very small quantities produced in peculiar... 

Phenolic acids are colorless in a dilute alcohol solution, but they may become yellow due to oxidation. From an organoleptic standpoint, these compounds have no particular flavor or odor. They are, however, precursors of the volatile phenols produced by the action of certain microorganisms (yeasts in the genus Brettanomyces and bacteria) (Section 8.3). Ethyl phenols, with animal odors, and ethyl gaiacols are found in red wines (Figure 6.4). In white wines, vinyl phenols, with an odor reminiscent of gouache paint, are accompanied by vinyl gaiacols. It has been clearly established that these compounds result from the... 

By isolating acetic bacteria, lactic bacteria and yeasts from red wines with phenol off-odors, it was demonstrated that Brettanomyces/Dekkera yeasts were the only microorganisms capable of producing several milligrams of ethyl-phenols per liter of wine. The species most prevalent in wine is Brettanomyces bruxellensis (Chatonnet et al, 1992b). 

One hypothesis suggests that yeasts in the genus Brettanomyces may play a role in the appearance of this defect (Ribereau-Gayon et al., 1975 Heresztyn, 1986a). Although their participation in mousiness has not been totally ruled out, it is now known that these contaminant yeasts are mainly responsible for phenol off-odors in red wines (Section 8.4.5). These off-odors result from the conversion of cinnamic acids into ethyl-phenols, which have an unpleasant odor reminiscent of horses and barnyards. 

The Ci4 intermediate (X = Br) resulting from treatment of the building block with the Cg unit Scheme 43) reacts with the C4 unit, obtained by reduction of ethyl acetoacetate by yeast (Y) to give the C g intermediate. This is then transformed into the hydroxyalkyl-substituted phenol of Scheme 40. 

Vanbeneden, N., Gils, R, Delvaux, R, Delvaux, R R. (2008). Formation of 4-vinyl and 4-ethyl derivatives from hydroxycinnamic acids occurrence of volatile phenolic flavour compounds in beer and distribution of padl-activity among brewing yeasts. Food Chemistry, 107, 221-230. http //dx.doi.Org/10.1016/j.foodchem.2007.08.008. 

Volatile phenols originate from hydroxycinnamic acids (ferulic, p-coumaric, or caffeic acid) by the action of hydroxycinnamate decarboxylase enzyme, which turn the hydroxycinnamics acid into vinylphe-nols (Albagnac, 1975 Grando et al., 1993). Then, these compounds are reduced to ethyl derivatives by vinylphenol reductase enzymes characteristic of species, such as Dekkera bruxellensis, Dekkera anomala, Pichia guillermondii, Candida versatilis, Candida halophila, and Candida mannitofaciens (Edlin et al., 1995 1998 Dias et al., 2003 Chatonnet et al., 1992 1995 1997 Dias et al., 2003), apart from very small quantities produced by some yeasts and lactic acid bacteria under peculiar growth conditions (Chatonnet et al., 1995 Barata et al., 2006 ... 

Tyrosol (Figure 6.5) or j9-hydroxy-phenyl-ethyl alcohol may be included in this group of compounds (Ribereau-Gayon and Sapis, 1965). It is always present in both red and white wine (20-30 mg/1) and is formed during alcoholic fermentation from tyrosine (j -hydroxyphenyl-alanine), in turn synthesized by yeast. This compound, which remains at relatively constant concentrations throughout aging, is accompanied by other non-phenolic alcohols like tryptophol (0-1 mg/1) and phenyl-ethyl alcohol (10-75 mg/1). 

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