3A Sparkling Wines and Yeast Autolysis 73
Feuillat 1993). It has been seen that, after bottle aging in contact with yeast, the
lipid content increases and there are qualitative and quantitative changes, depending
on the time of aging (Piton et al. 1988). Pueyo et al. (2000) used an HPLC method
with a light scattering detector to analyze the different families of lipids in induced
autolysis assays in a model wine. They detected lipids in the autolysate after 5 h, and
found these to decrease in the first two days, coinciding with the period of maximum
loss of yeast viability. This release of lipids is attributed by the authors to the action
of the hydrolytic enzymes on the cell wall, with the corresponding release of prod-
ucts to the surrounding medium. In the autolysates they detected triacylglycerols,
free fatty acids, sterol esters and sterols. Triacylglycerols and sterol esters were the
major lipids in the three strains studied.
The concentration of nucleic acids is also modified during autolysis (Alexan-
dre and Guilloux-Benatier 2006). In general, the concentration of nucleic acids
falls during aging and the extent of DNA degradation during autolysis depend on
the yeast strain used (Hernawan and Fleet 1995). This could possibly explain the
variability between the results reported. While some authors found that the DNA
was almost completely degraded after autolysis (Houg and Maddox 1970), others
found no decrease or only a partial degradation of DNA (Trevelyan 1978; Zhao and
Fleet 2003). The tendency of DNA to form complexes with proteins could protect
it, according to Hernawan and Fleet (1995), from the action of DNAses involved in
the autolysis.
RNA is also degraded during autolysis, and hydrolysis of around 95% has been
reported (Zhao and Fleet 2005). However, it is expected that in the conditions used
to elaborate sparkling wines (high ethanol concentration and low temperature and
pH), RNA degradation could be much lower.
RNA hydrolysis mainly produces 2’- ,3’- and 5’-ribonucleotides. Although mono-
phosphate nucleotides are well recognized in the food industry as flavour com-
pounds (Charpentier et al. 2005), further studies are required to know their impact
in the sensorial properties of sparkling wines.
Finally, several volatilecompounds are formed or released during autolysis
(Hidalgo et al. 2004; Molnar et al. 1981), some with low perception levels. Esters
are the major family of volatile compounds released during autolysis. Different
authors have related the quality of the sparkling wines to the concentration of esters,
such as isoamyl caproate, octyl acetate,phenylethyl acetate, phenylethyl caprate,
ethyl linoleate and diethyl succinate (Loyaux et al. 1981; Pozo-Bay ́on et al. 2003;
Pueyo et al. 1995). Although it is accepted that the secondary fermentation and lees
aging significantly alter the aromatic profile of sparkling wines (De La Presa-Owens
et al. 1998; Francioli et al. 2003), the impact of these compounds on the sensorial
properties of sparkling wines is poorly understood, and will be the subject of further
studies.
3A.4.3 Autolysis in the Winemaking Industry
Because of the slow nature of the natural process of autolysis, considerable research
has been aimed at accelerating this process. Two methods are currently available