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.

Recently, in Brazil, corn ethanol industries are being installed and the integration with sugar/energy-cane has been proposed, using bagasse for cogeneration and the juice to dilute the corn. However, this integration may have some limitations, such as the quality of the cane juice and potential contamination by microorganisms brought with the cane from the field. In this article, we first tested the effects of mixing energy cane juice with corn on fermentative parameters. We also assessed the effects of Lactobacilli. contamination on organic acids produced during the fermentation and fermentation parameters and proposed the use of ionizing radiation to replace antibiotics as a disinfection control method. Our results showed that mixing energy cane juice with corn does not have any negative effect on fermentation parameters, including ethanol production. The contamination with Lactobacilli. considerably increased the production of acetic, lactic, and succinic acid, reducing the pH and ethanol content from 89.2 g L⁻¹ in the sterilized treatment to 72.9 g L⁻¹ in the contaminated treatment. Therefore, for the integration between corn and cane to be applied on an industrial scale, it is essential to have effective disinfection before fermentation. Ionizing radiation (20 kGy) virtually disinfected the wort, showing itself to be a promising technology; however, an economic viability study for adopting it in the industry should be carried out.

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.

In very high gravity (VHG) fermentation, yeast cells are subjected to a multitude of challenging conditions, including the osmotic pressure exerted by the high sugar content of the wort and the stress factors associated with the high ethanol concentrations present at the end of the fermentation cycle. The response of this biological system to abiotic stresses may be enhanced through biochemical and physiological routes. Silica may play a significant role in regulating the cellular homeostasis of yeast. Alternatively, it is expected that this outcome may be achieved through biochemical responses from the effects of vitamins on yeast cells and the physiological yeast route changing by the culture medium aeration. The objective of this study was to investigate the effects of adding 500 mg L⁻¹ of silica on corn ethanol wort medium and the possibility of supplementing the same wort with vitamins alongside aeration (0.2 v v⁻¹ min⁻¹) as an alternative resource to sustain the fermentation yield rather than adding silica in a fed-batch fermentation cycle with yeast recycling. Upon completion of the five fermentation cycles, yeast samples subjected to the treatment with the addition of silica exhibited a 3.1% higher fermentation yield in comparison to the results observed in the vitamins plus aeration medium bath. Even though greater biomass production (19.1 g L⁻¹) was observed through aerobic yeast behavior in vitaminized supplemented corn medium, the provided silica had a more beneficial effect on yeast stress relief for very high gravity fermentation in a corn hydrolyzed wort with cell recycling.

The aim of this study was to investigate the mechanisms by which yeasts (Saccharomyces cerevisiae)control the toxic effects of aflatoxins, which are not yet fully understood. Radiolabeled aflatoxin B₁(AFB₁³H) was administered by gavage to Wistar rats fed with aflatoxin (AflDiet) and aflatoxin supplemented with active dehydrated yeast Y904 (AflDiet + Yeast). The distribution of AFB₁³H and its metabolites were analyzed at 24, 48 and 72 h by tracking back of the radioactivity. No significant differences were observed between the AflDiet and AflDiet + Yeast groups in terms of the distribution of labeled aflatoxin. At 72 h, for the AflDiet group the radiolabeled aflatoxin was distributed as following: feces (79.5%), carcass (10.5%), urine (1.7%), and intestine (7.4%); in the AflDiet + Yeast the following distribution was observed: feces (76%), carcass (15%), urine (2.9%), and intestine (4.9%). These values were below 1% in other organs. These findings indicate that even after 72 h considerable amounts of aflatoxins remains in the intestines, which may play a significant role in the distribution and metabolism of aflatoxins and its metabolites over time. The presence of yeast may not significantly affect this process. Furthermore, histopathological examination of hepatic tissues showed that the presence of active yeast reduced the severity of liver damage caused by aflatoxins, indicating that yeasts control aflatoxin damage through biochemical mechanisms. These findings contribute to a better understanding of the mechanisms underlying the protective effects of yeasts against aflatoxin toxicity.Graphical abstract