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Lignocellulosic materials and agro-industrial residues are essential in a sustainable biorefinery. The effective fermentation of renewable sugars is still an important challenge for an economically viable production of biofuels and biochemicals. This challenge involves biological aspects, such as choosing the microbial platform, and industrial aspects. These aspects can be assessed employing mathematical models to understand the complex synergies between the microorganism and processes. In this work, the performance of the yeast Spathaspora passalidarum was evaluated for the fermentation of xylose and glucose at different proportions, initial concentrations, and initial cell densities using an unstructured−unsegregated kinetic model. The likelihood confidence region, correlations between the parameters, and the convergence of the parameters through the optimization process were identified. It was also possible to identify that π Xyl, max , μ Glu, max , K ' S, Xyl , Y ' PEth/SGlu , Y ' PEth/SXyl , and Y ' X/SGlu were the most representative parameters, due to the high correlation (positive and negative) they have with the other model parameters. It was also possible to identify how initial substrate concentrations affected the specific uptake substrate and ethanol production rates; in this sense, the increase in the glucose concentration causes a decrease in the specific ethanol formation rate at a high concentration of xylose for S. passalidarum cultivated in the conditions proposed by this study.

Melle-boinot fermentation process can be used to increase the ethanol productivity in second-generation ethanol process (2G). However, bacterial contamination can result in decreased ethanol production and sugars consumption. The available literature on microbial contamination in the 2G at the secretome level, microbial interactions and their impacts on ethanol production are scarce. In this context, the cultivation of Spathaspora passalidarum was studied pure and in co-culture with Lactobacillus fermentum under conditions that mimic the Melle-boinot process. Glucose consumption and ethanol production by S. passalidarum were not affected by bacterial contamination. Xylose consumption was higher in pure culture (11.54 ± 2.62, 16.23 ± 1.76, 6.50 ± 1.68 g) than in co-culture fermentation (11.89 ± 0.38, 7.29 ± 0.49, 5.54 ± 2.63 g) in cycle 2. The protein profile of the fermented broth was similar in pure and co-culture fermentation. The low effect of L. fermentum on fermentation and protein profile may be associated with the inhibition of the bacteria by the low nutrient fermentation broth, with centrifugation and/or with sulfuric acid washing. Thereby, considering that research on microbial contamination in the 2G fermentation process is very limited, particularly at the omics level, these findings may contribute to the lignocellulosic biomass fermentation industry.