## 3 Results and Discussion
### Impact of Fermentation Parameters on Population Dynamics  
The first objective was to study how fermentation parameters such as nitrogen content, inoculum ratio, oxygenation, and temperature could impact the development of both yeasts: how their maximal growth rate and maximal population were modified and, mainly, which strain would be predominant throughout fermentation. Here, the aim was not to study the impact of chosen parameters independently as in previous studies, but simultaneously through the experimental design to allow for a comparison between effects. The impacts of fermentation parameters on variables describing the population dynamics are given in Table 3. For each parameter/variable couple, the standard effect, \(p\)-value, and contribution to variance are shown. The standardized effect provides information on the nature and level of the impact of the parameter on the variable: an increase in the parameter chosen leads to an increase in the variable studied when the standardized effect is positive, and to a decrease when the standardized effect is negative. The \(p\)-value provides information on the significance of this variation, and the contribution to variance indicates the importance of the parameter chosen in explaining the total variation of the variable studied. Regarding _Saccharomyces cerevisiae_, the growth rate \(\mu_{\rm max}\) was positively and significantly impacted by temperature (stand. effect 4.094) and not by the other factors (contribution to variance of 73.4% for temperature). In contrast, the growth rate of _Lachancea thermotolerans_ seemed to be impacted only by the inoculum ratio \(Sc/Lt\), and at the limit of significance (stand. effect \(-3.010\), \(p\)-value 0.057): \(\mu_{\rm max\,Lt}\) tended to be higher when the inoculum ratio favored \(Lt\). In this study, oxygenation had no impact on the growth rate of either yeast, whereas previous works showed a positive effect on the \(\mu_{\rm max}\) of \(Lt\)[20]. No significant effect of nitrogen content was observed here, despite nitrogen sources having been previously shown to influence the growth of yeasts differently according to the nature and quantity of nitrogen compounds [21; 35]. However, nitrogen content significantly impacted the growth rate only up to around 100 mg/L, depending on the species and strains of \(Sc\)[36]. As this \"limiting concentration\" was below both our chosen nitrogen levels (in line with our goal of avoiding nitrogen-scar conditions), this explained the lack of a significant effect of this particular parameter on growth rate. Thus, a decrease in temperature favored the faster development of \(Lt\) versus \(Sc\): the \(\mu_{\rm max\,Lt}/\mu_{\rm max\,Sc}\) ratio was indeed higher at 18 \({}^{\circ}\)C than at 28 \({}^{\circ}\)C (stand. effect \(-3.594\)), which supported previous results [16]. Although both \(Lt\) and \(Sc\) were able to grow at 15-20 \({}^{\circ}\)C and even better at 25-30 \({}^{\circ}\)C on YPD agar [37], temperature affected the population dynamics in mixed cultures [38; 39]. _S. cerevisiae_'s ability to grow at higher temperatures than most yeasts gives it an advantage: the temperature increase during fermentation can lead to its dominance versus non-_Saccharomyces_ species during wine fermentation [40; 41; 42; 43]. On the contrary, a decrease in temperature can enhance the growth and survival of non-_Saccharomyces_ yeasts by attenuating their susceptibility to ethanol [29; 44]. In addition, culture at low temperature could induce an increase in the intracellular level of ROS (reactive oxygen species) and an oxidative stress response (through mechanisms that are