16 F. Z a m o r a
P l a s m a M e m b r a n eCytoplasmeAcetyl-coAPhospholipids
Malonyl-coA½ O 2
H 2 OCO-ScoACOOHCOOHAcetyl-coA
carboxylaseCO 2NAPD+NADPH + H+
CO 2Saturated
Fatty Acid (SFA)Unsaturated
Fatty Acid (UFA)CO-ScoAFatty acid
sinthetaseMembrane
insertionP l a s m a M e m b r a n eCytoplasmeAcetyl-coAPhospholipids
Malonyl-coA½ O 2
H 2 OCO-ScoACO-ScoACOOHCOOHCOOHCOOHAcetyl-coA
carboxylaseCO 2NAPD+NADPH + H+
CO 2Saturated
Fatty Acid (SFA)Unsaturated
Fatty Acid (UFA)CO-ScoACO-ScoAFatty acid
sinthetaseMembrane
insertionDesaturaseOLE1P l a s m a M e m b r a n eGrape juiceCytoplasmeAcetyl-coAPhospholipids
Malonyl-coA2
H 2 OCO-ScoACOOHCOOHAcetyl-coA
carboxylaseCO 2NAPD+NADPH + H+
CO 2Saturated
Fatty Acid (SFA)Unsaturated
Fatty Acid (UFA)CO-ScoAFatty acid
sinthetaseMembrane
insertionP l a s m a M e m b r a n eCytoplasmeAcetyl-coAPhospholipidsMalonyl-coA(^2) H
2 O
CO-ScoACO-ScoACOOHCOOHCOOHCOOH
Acetyl-coA
carboxylase
CO 2
NAPD+
NADPH + H+
CO 2
Saturated
Fatty Acid (SFA)
Unsaturated
Fatty Acid (UFA)
CO-ScoACO-ScoA
Fatty acid
sinthetase
Membrane
insertion
Desaturase OLE1
SSSSSSSS
Fig. 1.8Synthesis of fatty acids in yeasts
Nevertheless, unsaturated fatty acids (UFA) need oxygen to be synthesised
(Alexandre et al. 1994). InSaccharomyces cerevisiae, UFA production is catalysed
by the desaturase OLE1 (Kajiwara et al. 2000). This enzyme is activated by low
temperatures and the presence of oxygen (Nakagawa et al. 2002). Afterwards, fatty
acids are used to synthesize phospholipids, which are inserted into the plasmatic
membranes.
Since oxygen is necessary to synthesize ergosterol and UFA, aeration during
alcoholic fermentation limits the growth ofSaccharomyces cerevisiae(Sablayrolles
and Barre 1986; Rib ́ereau-Gayon et al. 2000b) and the lack of oxygen may some-
times cause stuck and sluggish fermentations (Sablayrolles et al. 1996; Bisson 1999;