Ethanol production by Kluyveromyces marxianus ATCC 36907: Fermentation features and mathematical modeling

The effects of different temperatures (30 °C, 35 °C, 40 °C, and 45 °C) and initial glucose concentrations (50 g/L, 120 g/L, and 190 g/L) on the fermentative metabolism of Kluyveromyces marxianus ATCC 36907 were evaluated to optimize ethanol production. Mathematical models were developed based on experimental data to describe cell growth, substrate consumption, and ethanol production. Various kinetic models integrated with material balances were examined. The Akaike information criterion (AIC) was employed to identify the most accurate model representing the experimental behavior. Interestingly, the ethanol production rate was independent of the growth rate of K. marxianus. The growth kinetics indicated that the growth rate could be controlled by the oxygen concentration, which was influenced by cell concentration rather than glucose consumption. A desirability function was utilized to optimize ethanol productivity, substrate conversion efficiency and temperature, considering the conditions for future applications in simultaneous saccharification and fermentation (SSF) processes. The optimized experimental conditions obtained were validated, resulting in a new model specific to these conditions. This new model analysis confirmed the achievement of the objective to prioritize ethanol production. The optimized conditions for maximum ethanol production were initial glucose concentration of 91 g/L and temperature of 40 °C. Under these conditions, the ethanol concentration reached 12 g/L, with glucose conversion efficiency into ethanol of 0.13 g/g and productivity of 1.09 g/L/h after 11 h. This approach provided valuable insights into the fermentative behavior of K. marxianus, serving as a foundation for the design, optimization, and process control in biorefineries. •The approach allowed an expanded comprehension of the yeast fermentative metabolism.•Ethanol production was not associated to biomass growth.•The oxygen limitation was quite determinant for the fermentative metabolism.•Different fermentation conditions were evaluated to maximize the ethanol production.•Optimized conditions can be used in SSF processes with Kluyveromyces marxianus.