Search

Yeast recycling, which is a common practice in sugarcane ethanol plants, could be expanded if it could be successfully implemented in corn-based ethanol production. However, the process of recycling the yeast remaining after fermentation is hampered by contaminating microorganisms that reduce the fermentation efficiency and compete with the yeast for the fermentable sugars. Currently, antibiotics are used to control microbial contamination. This study proposes chlorine dioxide and electron beam irradiation as alternative control methods for completely inactivating contaminants and minimizing their effect on recycled yeast. For that, wort sterilization using electron radiation (20 kGy) and treatment with a chemical biocide, namely chlorine dioxide (125 mg kg−1), were compared with non-treated wort. Five fermentation cycles were performed using fed-batch systems with 300 g L−1 of fermentable sugars. The results obtained in this study showed the inactivation of contaminants under the effect of electron beam irradiation, which led to an increase in the productivity, yield, and efficiency of fermentation by 0.21 g L−1h−1, 2.6%, and 4.7%, respectively. However, ClO2 did not show promising results in reducing contamination or improving fermentative parameters. Thus, electron beam irradiation of contaminated wort may be a suitable alternative to chemical biocides and would allow the use of recycled yeast in corn-based ethanol plants.

High-gravity fermentation, used for ethanol production from sugarcane, corn, and mixed substrates, offers several benefits. Yeast, a rapidly multiplying unicellular microorganism, can be adapted for high sugar and ethanol tolerance on a lab scale. However, different substrates can enhance fermentation efficiency. Our study consisted of two experiments. In the first, we compared simple batch feeding with a fed-batch system for yeast selection in high-gravity fermentation. We ran eight cycles with increasing initial sugar contents (50 to 300 g L−1). No significant differences were observed in the first seven cycles, but in the eighth, the fed-batch system showed lower glycerol and fructose contents and higher cell viability than the simple batch system. In the second experiment, we used the fed-batch system with 300 g L−1 from sugarcane, corn, and mixed wort. The results showed that mixed wort produced higher ethanol contents and greater fermentation efficiency compared to corn and sugarcane as substrates. In conclusion, our findings indicate that the fed-batch system is more suitable for high-gravity fermentation on a lab scale, and the combination of sugarcane juice and corn can enhance fermentation efficiency, paving the way for integrating these substrates in industrial ethanol production.

Corn and sugarcane are the primary feedstocks for ethanol production, but microbial contamination hinders yeast fermentation efficiency. Current control methods include antibiotics and sulfuric acid, but they have limitations, resulting in dependence on external inputs and the risk of antibiotic-resistant bacteria. This review examines electron beam technology as an industrial-scale disinfection solution for both corn- and sugarcane-based ethanol production, highlighting its advantages, limitations and opportunities for adoption in Brazil. A critical evaluation highlights the importance of optimal operating conditions for scalability, cost effectiveness and sustainable implementation. Through a practical example, we demonstrate the effectiveness of electron beam treatment in improving fermentation efficiency and reducing contamination-related losses. Notably, the ionizing radiation from this process does not affect wort sugar content or generate radioactive residues. While acknowledging the potentially high energy input requirements, cogeneration in sugarcane mills can address this, making it a viable option; however, further technical and economic evaluation should be made. In addition, electron beam technology is a promising approach for the production of high-value products such as neutral alcohol, amino acids, animal feed and pharmaceuticals. Therefore, this comprehensive review provides valuable insights for researchers, industry stakeholders and policymakers to promote sustainable and efficient ethanol production practices.