# Study on the Kinetic Model of Mixed Fermentation by Adding Glutathione-Enriched Inactive Dry Yeast
## 4 Discussion  
The increasing recognition of _T. delbruechi_'s role in wine aroma has stimulated research on its fermentation products, metabolic and evolutionary pathways, and potential synergies with other yeasts to enhance fermentation performance [36; 37]. Multistarter fermentations with non-_Saccharomyces_ and _Saccharomyces_ strains can simulate natural fermentation [38; 39], reduce the risk of fermentation failure, and facilitate the study of strain interactions, overcoming the variability of natural fermentation. The interactions among different yeasts influence the aroma compounds and the metabolic pathways of yeast. These interactions are also modulated by the fermentation environment [40]. Yeast derivatives can alter some components of the fermentation medium, so their effects on microbial growth need to be investigated. Unlike previous studies, we used simulated grape juice to minimize the influence of other factors, and we explored the effects of different doses of g-IDY on wine aroma, yeast growth, and metabolic kinetics. [PERSON] et al. [41] investigated the nitrogen source preference of commercial non-_Saccharomyces_ yeasts by conducting pure culture and sequential culture fermentations in synthetic grape musts with adjusted nitrogen contents. [PERSON] et al. [42] studied the effects of _S. cerevisiae_ and _Dekera bruxellensis_ on wine aroma by constructing a double-compartment membrane system with synthetic wine must and found that it could reduce the content of ethylphenols and enhance the formation of aromatic esters. Wine fermentation is a stressful environment for yeast. Several environmental stresses, including pH shock, ethanol toxicity, nutrient starvation, and oxidative stress, can individually or collectively affect yeast physiology deleteriously. Under these conditions, genomic adaptation of yeast to cope with the adverse effects of the stress factors occurs [43; 44; 45]. Ethanol stress can increase the production of reactive oxygen species (ROS) in yeast, which can damage the yeast structure and cause cell death [46]. GSH is a key molecule that protects yeast from oxidative damage. It scavenges ROS, such as H\({}_{2}\)O\({}_{2}\) non-enzymatically, and acts as a cofactor for various antioxidant enzymes to cope with stressful environments. GSH also helps yeast maintain the integrity and adaptation of the mitochondrial genome [43] and serves as a source of sulfur or nitrogen under nutrient limitation [47; 48]. GSH exhaustion negatively impacts both the electron transport chain function and the chronological life span of yeast [49]. However, the GSH level in yeast varies depending on the experimental conditions [50; 51; 52]. The yeast population may increase due to the uptake of GSH from g-IDY by yeast cells, which protects the yeast structure and reduces the oxidative stress in yeast [49]. Moreover, g-IDY can also release polysaccharides and peptides that affect yeast metabolism and the aroma profile of wine [33]. The aroma compounds generated during fermentation influence the perception of the final wine aroma. Adding g-IDY can increase the content of phenylethanol, a floral compound, by enhancing the GSH-mediated reduction in phenylacetaldehyde by alcohol dehydrogenase [53; 54; 55]. Phenylethyl acetate, another floral compound, is formed by the esterase-catalyzed reaction of acetic acid and phenylethanol [56]. It may be that the yeast synthesizes more phenylethanol, which is subsequently converted by esterase into more phenylethanol acetate. We used nonlinear regression models to fit the yeast growth, sugar consumption, and ethanol production data during wine fermentation. The Logistic model fitted the yeast growth better, and the Boltzmann model fitted the sugar consumption and ethanol production better. Both models captured the kinetics of co-fementation well. Our results agreed with those of [PERSON] et al. [57] for the Logistic model and [PERSON] et al. [27] for the Boltzmann model, with R\({}^{2}\) values above 0.99.