According to bibliographical research, there is no reference to a mixed culture that mentions the critical ethanol tolerance of 30–35 gL−1 for S. stipitis. The proposed strategy of culture sequence, which consisted of the addition of S. cerevisiae ITV-01 and molasses “B” to fermentation medium with S. stipitis NRRL Y-7124 in sugarcane bagasse hydrolyzate enriched with molasses “B” can produce 53.80 gL−1 ethanol, generating expectations for further interest in improving the process controlling such conditions as oxygen supply, pH, as well as conditions of continuous or fed batch culture.
4. Conclusions
Ethanol fermentation without xylitol production by S. stipitis NRRL Y-7124 and S. cerevisiae ITV-01 was favored through using molasses “B” to enrich sugarcane bagasse hydrolyzate. In co-culture a significant increase in ethanol concentration (53.80 gL−1) was obtained when S. cerevisiae ITV-01 and molasses “B” were added to the fermentation medium with S. stipitis NRRL Y-7124 (50% sugarcane bagasse hydrolyzate enriched with molasses “B”) at 42 h, when sugars were exhausted. The use of a sequential fermentation process proved to be a favorable strategy to increase ethanol concentration (74% more) above the critical tolerance limit for S. stipitis NRRL Y-7124. Furthermore studies should be carried out in order to evaluate oxygen supply using the sequential culture strategy proposed.
Acknowledgments
The authors acknowledge the economical support from the National Council of Science and Technology, Mexico (CONACYT-FOMIX VERACRUZ, grant number 128052) and the critical reading of Patricia Hayward Jones MSc. and Dulce M. Barradas Dermitz, M Sc.