## 4 Discussion
cerevisiae_, showed high compatibility as only the positive oenological attributes were observed when they were used in a co-inoculation mode. Similar results were observed when _S. cerevisiae_ was inoculated with _T. delbrueckii_, but only under sequential fermentation [31]. The aromatic profile of the produced Sauvignon blanc wines of the present study exhibited significant differences concerning their chemical composition and their sensory traits, highlighting the metabolic interactions not only at species and strains level, but also in different yeast inoculation ratios. The majority of the volatile metabolites that were produced by the yeasts during alcoholic fermentation process belong to the group of higher/fuel alcohols and esters [34; 35; 36; 30]. The concentration of these aroma compounds is highly dependent on the factors such as the yeast species or strains that are used, but also on the grape variety and the oenological techniques that are used [34; 37]. However, how these aromatic compounds contribute to the wine organoleptic profile is highly dependent on their perception threshold as well as on the forming perception interactions [22]. The wine ranked as the more complex with the greater global mark was the one fermented under the Sc2 30%-Sp2 70% inoculation scheme. Interestingly, the produced wine was characterized by intermediate higher alcohols and esters concentration when it was compared to the other tested fermentation schemes. For instance, higher alcohols can even provoke a masking effect on the wine's fruity notes through perception interactions or giving 'heavier' aromas. The aroma perception depends on the volatiles distribution between the matrix and the gas phase highly affecting the final organoleptic characteristics [38]. Additionally, the non-volatile compounds of wine such as polysaccharides and proteins may also have an impact on the volatility and aroma perception [39]. On the other hand, the produced volatile thiols had a clear effect on the wine's sensory traits. Volatile thiols mostly develop during alcoholic fermentation through the action of yeast cells from odorless grape precursors [9; 18]. As these compounds are linked to the varietal aromas of Sauvignon blanc, extended research has been focused on that grape variety and the factors affecting their generation. Inevitably, their final concentration in wine is highly dependent on the yeast species and the strain that are used as well as on environmental parameters such as the fermentation temperature, copper sulphate supplementation, the YAN levels and its infection by _Botrytis cinerea_[12; 35]. Our results clearly showed that the inoculation scheme, in pure or mixed cultures of _S. cerevisiae_ and _S. pastorianus_ affected the production of varietal thiols and directly influenced the wine's sensory profile. Interestingly, the presence of _S. pastorianus_ in the mixed cultures either with Sc1 or Sc2 in a ratio of 70%-30% significantly increased the total thiols production compared to monocultures. This result highlighted not only the species effect, but also the importance of the inoculation ratio [11]. On the contrary, the 3 MHA production level was always decreased in the mixed inoculation cultures. In the case of 3 MHA, similar results were obtained when _S. cerevisiae_ was inoculated with _T. delbrueckii_[36]. In the latter study, the concentration level of 3 MHA in the wines that were fermented with mixed cultures was significantly decreased compared to the wines that were fermented with pure cultures of the _S. cerevisiae_ strain [36]. 3 MHA is produced from 3 MH during grape must fermentation by the action of a yeast ester-forming alcohol acetyltransferase through an acetylation reaction, which is encoded by the _atflp_ gene [35; 40; 41].