Sterilized and raw tequila vinasse as a medium for ethanol production via S. cerevisiae and K. marxianus: Estimation and comparison of its kinetic parameters

Tequila production generates vinasse as wastewater that may be valorized to produce ethanol. To assess vinasse’s value as a source of biofuel in circular bioeconomy, culture media were formulated with sterilized and raw vinasse using glucose as model substrate and two conventional yeasts, for comparison. One of them is S. cerevisiae, and the other strain, K. marxianus, was isolated from a tequila vinasse. In sterilized vinasse, results suggest that both yeasts activate secondary metabolic pathways as stress response to inhibitory compounds and salt, being S. cerevisiae the strain that showed better ethanol production (1.3 g L⁻¹ h⁻¹). However, such a remark is opposite when K. marxianus was subjected to ALE strategy to improve its tolerance to vinasse’s stressors. Adapted K. marxianus enhanced its ethanol production (1.2 g L⁻¹ h⁻¹) as compared to S. cerevisiae (1.1 g L⁻¹ h⁻¹) in raw vinasse. To quantify how media and strains affect ethanol production, a dynamic mathematical model was formulated, and its parameter values were fitted for each scenario. A comparison of such values shows that ALE strategy adequates the reaction rate to the media, agreeing with experimental data. Both the maximum reaction rate and the half velocity constant increased after ALE, when considering a Monod reaction rate; thus, leading to a quicker reaction and to a reaction rate that saturates at larger substrate concentrations. In turn, the parameters values with both yeasts are similar to each other. These results confirm that tequila vinasse medium is suitable for ethanol production.