Assessing Ionizing Radiation and Chlorine Dioxide (ClO2) as Potential Aseptization Treatments for Yeast Recycling on Mixed Wort of Corn and Sugarcane in Brazil

Abstract

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.

Electron Beam on Fermentation Medium as an Alternative Disinfection Method for Ethanol Distilleries: A Comprehensive Review

“…Certain antibiotics, such as virginiamycin, persist in both yeast and distiller's dried grains (DDGs), resulting in undesired residual effects in high-quality animal feed products [45]. This applies to commercialized yeasts, WDG or DDG [32].…”

“…To mitigate these issues, it is important to carefully monitor and control the fermentation process, as the presence of wild yeasts can cause problems such as yeast cell flocculation, excessive foam formation and reduced yeast cell viability, leading to decreased process productivity and efficiency indicators [31]. These effects result in several losses during the yeast recovery process (Melle-Boinot) [32,33], including: i.…”

“…Contamination also prevents the production of wine with consistent microbiological characteristics throughout the season, which, in turn, hinders the production of specialty alcohols such as neutral alcohol. Another negative effect of contamination is the lack of stability in the non-aseptic production process, which makes potentially applicable techniques and technologies not feasible [25], including practices such as recycling and recovery of the same standard yeast strain [32,34,35].…”

“…Based on the experience reported in production systems, ionizing radiation can be an effective alternative for the elimination of pathogenic and spoilage microorganisms [32,50,51]. This technology has been successfully tested by various researchers as a means of controlling microorganisms in sugary solutions [47,52,53] while preserving the nutritional and sensory qualities of the material [54].…”

“…Electron beams are released from the cathode, also called cathode rays. The accelerated electrons are characterized by low penetration and high dose rate (kGy s −1 ) [32], which significantly reduces the treatment time of the material [65]. This characteristic makes it possible to use the electron beam in production lines with high throughput [32,54].…”