11 Wine Spoilage by Fungal Metabolites 627
11.3.1 Chemical Structure and Occurrence
Volatile phenols are a group of molecules included in the non-anthocyanin pheno-
lic compounds of white and red wines. The chemical structure of VP are charac-
terised by a phenolic ring and a radical with different compositions (Fig. 11.4).
The main volatile phenols of wines are 4-vinylphenol (4-VP), 4-vinylguaiacol
(4-VG), 4-vinylcathecol (4-EC), 4-vinylsyringol (4-VS) and their respective reduced
forms 4-ethylphenol (4-EP), 4-ethylguaiacol (4EG), 4-ethylcathecol (4-EC) and
4-ethylsyringol (4-ES). These molecules occur in wines with different concentra-
tions, being vinylphenols typically associated with white wines and ethylphenols
with red wines. Table 11.3 shows recent results on the average concentration range
of these molecules in wines. In addition, vinylphenols may be also present in red
wines as anthocyanin-vinylphenol adducts, like malvidin 3-glucoside-4-vinylphenol
(Cameira-dos-Santos et al. 1996) and similar 4-VP, 4-VC and 4-VS derivatives
(Schwarz et al. 2003; Su ́arez et al. 2007).
11.3.2 Origin
11.3.2.1 Availability of Precursors
The precursors of VPs are hydroxycinnamic acids which are enzymatically decar-
boxylated by a cinnamate decarboxylase, leading to vinylphenol derivatives, and
Fig. 11.4Conversion of hydroxycinnamic acids to vinylphenols and ethylphenols (reprinted from
Su ́arez et al. 2007, permission to be obtained)