Fermentation Cycle Research Articles

Tracing the change of the volatile compounds of soy sauce at different fermentation times by PTR-TOF-MS, E-nose and GC–MS

Proton-transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS), combined with electronic nose (E-nose), was first used to track the change of volatile organic compounds (VOCs) in soy sauce in this study. The results showed that 163 VOCs with different mass numbers were identified. Based on the differences in VOCs, the entire fermentation cycle was divided into four stages (0D and 15D; 30D-75D; 90D; 105D120D). The key stage of aroma formation was on day 90, when the VOC content reached its peak. It was clear that the key feature differential component was nonanal and phenethyl acetate by partial least squares discriminant analysis model, which showed significant correlation with the fermentation time. Moreover, the Quadratic Discriminant Analysis and Linear Discriminant Analysis models can accurately predict the fermentation cycle of soy sauce. The results of study demonstrated the potential of PTR-TOF-MS for comprehensive online monitoring and distinguishing of VOCs change during soy sauce fermentation.

High-Throughput Screening for Enhanced Thermal Stability of Inherently Salt-Tolerant l-Glutaminase and Its Efficient Expression in Bacillus licheniformis.

In addressing the challenges posed by extended fermentation cycles and high-salt conditions in high-salt liquid-state fermentation soy sauce (HLFSS) production, a high-throughput screening method was devised to identify thermally stable l-glutaminase mutants. This study yielded mutants A146D and A51D, exhibiting enhanced thermal stability. Computer-aided analysis revealed that these mutations introduced additional forces, compacting the protein structure and lowering the Gibbs free energy, thereby improving thermostability. Furthermore, the incorporation of aspartic acid augmented the negative surface charge, contributing to superior salt tolerance compared to the wild type (WT). Notably, in a 25% NaCl buffer, A146D and A51D demonstrated half-lives of 72.57 and 71.31 day, respectively, surpassing the WT's 59.08 day. In a 5 L bioreactor, the optimal mutant A146D achieved a remarkable enzymatic activity of 2800.78 ± 98.1 U/mL in recombinant Bacillus licheniformis fermentation broth, setting a new benchmark. This research offers valuable insights and a foundation for the modification and application of l-glutaminase in the food industry, particularly in HLFSS brewing.

Gellan-amino acid hydrogel-based bioreactor for optimizing the production of yeast metabolites

Hydrogels mimic natural environments due to their hydrated, polymeric networks which are beneficial for microorganism growth. The substantial water content maintains a consistently moist environment, and porous structure of hydrogel promotes efficient nutrient transfer and cell distribution, offering advantages over traditional liquid bioreactors. While their application in cell immobilization for bioconversion is well-known, their use as a solid-state fermentation matrix remains unexplored. This study is the first attempt to integrate gellan and amino acids to develop an innovative hydrogel bioreactor. The performance of this system was determined by cultivating Rhodosporidium sp. (MTCC 9733) as a model organism and evaluating its metabolite production. Further, gellan and amino acids concentration was optimized using one-factor-at-a-time and D-optimal response surface methodologies to produce β-carotene, lipid, and protein. Additionally, a comparison of productivity, yield, and process economics suggested that novel solid-state hydrogel fermentation approach outperformed classical submerged fermentation in YMB liquid media. Moreover, rheological properties of optimized hydrogel, conducted before and after yeast cultivation, revealed that this system possesses significant mechanical strength and structural integrity. Such attributes render the hydrogel suitable for utilization across multiple fermentation cycles. Hence, this study illustrates the potential of gellan-amino acid hydrogels as sustainable, efficient alternatives to conventional fermentation methods.

The potential Impact of bacterial probiotics on ruminal greenhouse gases production in vitro of dietary Delonix regia seeds in rams and steers.

This study aimed to evaluate the influence of probiotic bacteria (Pediococcus acidilactici BX-B122 and Bacillus coagulans BX-B118) on methane, carbon monoxide, and hydrogen sulfide, and fermentation profile of dietary Delonix regia seeds in ruminant. Ruminal contents from slaughtered rams and steers were used as inoculum for in vitro fermentation system. The total gas, methane, carbon monoxide, and hydrogen sulfide volume, as well as pH and dry matter degradability, were quantified in three fermentation cycles. Probiotic bacteria reduced the production of methane and hydrogen sulfide, while also increasing (P < 0.05) dry matter biodegradability, short-chain fatty acids, and metabolizable energy in both rams and steers. Delonix regia seeds at 6, 12, and 18% reduced total gas production. Higher production of methane and carbon monoxide was observed in rams compared to steers. Interestingly, no impact (P > 0.05) on the pH of the ruminal contents was found in Delonix regia seeds alone or in combination with probiotics. However, higher (P < 0.05) methane conversion efficiency (i.e., ratios of methane: short-chain fatty acids, methane: metabolizable energy, and methane: organic matter) was observed in experimental diets with Delonix regia seeds compared to diets containing both Delonix regia seeds and probiotic bacteria. In conclusion, dietary inclusion of 6, 12, and 18% of Delonix regia seeds with probiotic bacteria (Pediococcus acidilactici BX-B122 and Bacillus coagulans BX-B118) can mitigate the production of methane and hydrogen sulfide, while also increasing dry matter biodegradability, short-chain fatty acids, and metabolizable energy both ruminant animals.

ARTP/NTG Compound Mutagenesis Improved the Spinosad Production and the Insecticidal Virulence of Saccharopolyspora Spinosa.

Spinosad is an efficient and broad-spectrum environmentally friendly biopesticide, but its low yield in wild-type Saccharopolyspora spinosa limits its further application. ARTP/NTG compound mutagenesis was used in this study to improve the spinosad titer of S. spinosa and obtain a high-yield mutant-NT24. Compared with the wild-type strain, the fermentation cycle of NT24 was shortened by 2 days and its maximum titer of spinosad reached 858.3 ± 27.7 mg/L, which is 5.12 times more than for the same-period titer of the wild-type strain. In addition, RT-qPCR, resequencing, and targeted metabolomics showed that the upregulation of the key differential genes accD6, fadD, sdhB, oadA, and gntZ caused increased metabolic flux in the tricarboxylic acid cycle and pentose phosphate pathway, suggesting that the accumulation of pyruvate and short-chain acyl-CoA was the primary cause of spinosad accumulation in NT24. This study demonstrates the effectiveness of ARTP mutagenesis in S. spinosa, and provides new insights for the mechanism of spinosad biosynthesis and metabolic engineering in S. spinosa.

Spent yeast reuse as inoculum: a strategy to boost cellulosic ethanol productivity

AbstractFor the implementation of an integrated biorefinery into a pulping mill, the valorization of bark through cellulosic ethanol production and simultaneously the valorization of the residual yeast from each fermentation run should be considered to increase sustainability and pulp and paper profitability. Spent yeast recycling during cellulosic ethanol production is an opportunity to reduce waste according to environmental issues for disposal at the industrial level, boosting the circular economy. This work evaluated the reuse of spent yeast in successive fermentation experiments at Erlenmeyer and bioreactor scales for cellulosic ethanol from Eucalyptus globulus bark. The spent yeast recovered through centrifugation at the end of each experiment was used as inoculum for subsequent batch fermentation. Across five sequential fermentations, wherein only a fraction of spent yeast was recycled, a discernible decline in ethanol volumetric productivity was observed throughout successive fermentation cycles. Conversely, employing the complete spent yeast for recycling along 11 consecutive trials resulted in a notable enhancement of ethanol productivity, as evidenced by a reduction in fermentation duration to approximately one-third remaining the conversion efficiency above 70%. Four successive experimental trials were conducted at the bioreactor scale, resulting in volumetric productivities ranging from 2.00 to 5.83 g L−1 h−1. The reuse of spent yeast in consecutive fermentation cycles demonstrably augmented productivity, thereby validating a promising strategy for the industrial-scale production of cellulosic ethanol. This significantly contributes to advances in the circular economy principles within the overarching framework of biorefinery operations. Graphical Abstract

Exploring Calcium Alginate-Based Gels for Encapsulation of Lacticaseibacillus paracasei to Enhance Stability in Functional Breadmaking.

This study focuses on evaluating the efficiency of acid-tolerant Lacticaseibacillus paracasei bacteria encapsulated in an alginate-based gel matrix during repeated sourdough fermentation cycles, as well as their preservation during storage and throughout baking at high temperature. A double-coating procedure was applied, involving the encapsulation of bacterial cells in calcium alginate, which was further coated with chitosan. The encapsulation efficiency (EE) did not show significant difference between alginate and alginate-chitosan (97.97 and 96.71%, respectively). The higher number of L. paracasei bacteria was preserved in double-coated microbeads, with survivability rates of 89.51% and 96.90% in wet and dried microbeads, respectively. Encapsulated bacteria demonstrated effective fermentation ability, while double gel-coated cells exhibited slower acidification during sourdough fermentation, maintaining higher efficiency in the second fermentation cycle. The addition of freeze-dried, alginate-based gel-encapsulated bacteria (2-4%, w/w flour) significantly (p < 0.05) improved bread quality and extended its shelf life. A double-layer coating (alginate-chitosan) can be introduced as an innovative strategy for regulating the release of lactic acid bacteria and optimizing fermentation processes. Powdered alginate or alginate-chitosan gel-based L. paracasei microcapsules, at appropriate concentrations, can be used in the production of baked goods with acceptable quality and sensory properties, achieving a lactic acid bacteria count of approximately 106 CFU/g in the crumb, thereby meeting the standard criteria for probiotic bakery products.

Co-culturing Bifidobacterium animalis ssp. lactis with Lactobacillus helveticus accelerates its growth and fermentation in milk through metabolic interactions

[Objective] This study aimed to investigate the interaction between Lactobacillus helveticus H9 (H9) and Bifidobacterium animalis ssp. lactis Probio-M8 (M8) through metabolomics analysis, focusing on understanding how co-culturing these strains can enhance bacterial growth and metabolism, thereby shortening the fermentation cycle and improving efficiency. [Methods] The H9 and M8 strains were cultured individually and in combination (1:1 ratio) in milk. The fermented milk metabolomes were analyzed using solid-phase microextraction-gas chromatography-mass spectrometry. [Results] In the dual-strain fermentation, the M8 strain exhibited a 2.33-fold increase in viable bacterial count compared with single-strain fermentation. Additionally, the dual-strain fermentation resulted in greater metabolite abundance and diversity. Notably, the dual-strain fermented milk showed significantly elevated levels of metabolites, including 5-methyl-2-hexanone, (E)-3-octen-2-one, acetic acid, alanine, and 3-hydroxy-butanal. [Conclusion] Our results demonstrated that co-culturing the M8 and H9 strains accelerated growth and fermentation efficiency. This enhancement effect is likely attributed to the strong proteolytic ability of the H9 strain, which hydrolyzes casein to produce small molecular peptides, alanine, tyrosine, and other growth-promoting factors. The insights gained from this study have significant implications for probiotics and the dairy industry, potentially leading to shorter fermentation cycles, enhanced cost-effectiveness, and improved nutritional and functional properties of future fermented milk products. Additionally, these findings may contribute to advancements in probiotic research and applications.

Enhancing bioprocessing of red pigment from immobilized culture of gamma rays mutant of the endophytic fungus Monascus ruber SRZ112

Considerable attention has been paid to exploring the biotechnological applications of several Monascus sp. for pigment production. In this study, our focus is on enhancing the bioprocessing of red pigment (RP) derived from the endophytic fungus Monascus ruber SRZ112. To achieve this, we developed a stable mutant strain with improved productivity through gamma irradiation. This mutant was then employed in the immobilization technique using various entrapment carriers. Subsequently, we optimized the culture medium for maximal RP production using the Response Surface Methodology. Finally, these immobilized cultures were successfully utilized for RP production using a semi-continuous mode of fermentation. After eight cycles of fermentation, the highest RP yield by immobilized mycelia reached 309.17 CV mL−1, a significant increase compared to the original titer. Importantly, this study marks the first report on the successful production of Monascus RP in a semi-continuous mode using gamma rays’ mutant strain, offering prospects for commercial production.

Rederiving kinetics to model biohydrogen production from immobilized microalgae alginate beads at various polymerization degrees of alginate under dark fermentative environment

The performance of immobilized microalgae-alginate beads on biohydrogen production and its stability across several dark fermentation cycles is influenced by the sodium alginate concentrations. Thus, it is vital to determine the optimal condition for immobilization to achieve maximum encapsulation efficiency, stability and biohydrogen production. In this work, different sodium alginate concentrations (2 to 8 w/v%) were used to immobilize microalgae in influencing the dark fermentative biohydrogen productions from municipal wastewater, and its reusability was also investigated. The immobilized microalgae-alginate beads with sodium alginate concentration of 2 % showed the lowest stability and biohydrogen production in all cycles. The highest biohydrogen production was achieved by immobilized microalgal-alginate beads prepared from 8 % sodium alginate, followed by 6 % and 4 % in the first and second cycles. However, 8 % of immobilized microalgae-alginate beads generated the lowest biohydrogen volume during the third cycle. Besides, a model was rederived from the modified Gompertz model and Fick's law of diffusion equation to describe the relationship between polymeric viscosity and biohydrogen production from immobilized microalgae-alginate beads with different sodium alginate concentrations. As the sodium alginate concentrations increased, the viscosity also increased which significantly affected the properties of immobilization matrix formed such as encapsulation efficiency, growth of microalgae, diffusion of substrate and biohydrogen yield. The rederived model managed to fit the experimental data with a coefficient of determination values of >0.95 for all the polymerization degrees of alginate. The kinetic parameters, namely, yield of biohydrogen and specific microalgae growth rate of sodium alginate concentration of 6 % were 129.80 L kg−1 and 4.69 h−1, respectively, which were considered as maximum results as compared with other sodium alginate concentrations. Besides, the difference in biohydrogen productions for all cycles and kinetic data of biohydrogen yields obtained from the rederived model between sodium alginate concentration of 6 % and 8 % only exhibited a slight variance (<3 %). Thus, sodium alginate concentration of 6 % was considered to be an optimal for immobilizing microalgae in performing the dark fermentation. Overall, the results revealed the significance of suitable sodium alginate concentration in maximizing the immobilization of microalgae for performing the dark fermentative biohydrogen production.

Prospects for cordycepin biosynthesis in microbial cell factories

Cordycepin, an adenosine analog, exhibits diverse bioactivities and holds significant potential for applications in healthcare and agriculture. Fungi of the genus Cordyceps, such as Cordyceps militaris, can naturally produce cordycepin. Current sources of cordycepin primarily involve extraction from fruiting bodies or isolation from liquid fermentation using C. militaris, presenting challenges such as low production intensity, complex separation and purification systems, and high production costs, limiting industrial feasibility. Recent advancements have witnessed the utilization of various fungal chassis cells to successfully engineer heterologous biosynthetic platforms for cordycepin, such as Saccharomyces cerevisiae and unconventional yeasts, offering advantages of high yield, short fermentation cycles, and a broad substrate spectrum. This mini review summarizes the biosynthetic pathways of cordycepin and focused on the comparison of the characteristics, advantages, current performance and prospects for the microbial cell factories, analyzing potential targets for metabolic pathway modification and giving strategies in both genetic engineering and process engineering to enhance production intensity. The mini review particularly emphasizes the crucial role of chassis cell stress tolerance to the toxic product in determining cordycepin yield and highlights the urgent need for high-throughput screening methods for high-yield strains.

Silica Wort Supplementation as an Alternative for Yeast Stress Relief on Corn Ethanol Production with Cell Recycling

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.

Revealing the key microorganisms producing higher alcohols and their assembly processes during Jiang-flavor Baijiu fermentation

Excessive levels of higher alcohols have negative impacts on the quality of Baijiu. Understanding the key microorganisms responsible for producing higher alcohols and their assembly processes is crucial for controlling higher alcohols in multi-species Baijiu fermentation. This study investigated the changes in volatile compounds, including higher alcohols, and microbial communities in the four fermentation cycles of Jiang-flavor Baijiu. Higher alcohols were the most abundant in the first cycle. Through metatranscriptomic and culture-dependent analysis, Saccharomyces cerevisiae and four non-Saccharomyces yeasts (Pichia kudriavzevii, Zygosaccharomyces bailii, Schizosaccharomyces pombe, and Torulaspora delbrueckii) were demonstrated to be the main contributors to higher alcohol (isobutanol, isoamylol, and 1-propanol) production, with S. cerevisiae producing the highest levels. A higher abundance of Saccharomyces resulted in the highest levels of higher alcohols in the first cycle. Moreover, our results revealed that yeast community was assembled from stochastic to deterministic processes with the increase of fermentation cycles, driven by lactic acid. These findings provide valuable insights into controlling higher alcohol production in Baijiu fermentation.

Pre-adaptation of yeast (Saccharomyces cerevisiae) strains to very high gravity can improve fermentation parameters and reduce osmotic stress

AbstractThis study investigated improvements in sugarcane ethanol production by adapting yeast strains for very high gravity fermentation. Two yeast strains (C22 and Y904) were adapted in eight fermentation cycles with increasing initial sugar content from 56.2 to 296.1 g L−1(Experiment 1). After the last cycle, the “adapted” yeasts were recycled in a wort containing 296.1 g L−1initial sugar and compared with their respective strains that were not subjected to the adaptation process (Experiment 2). Fermentative parameters were analyzed and the osmotic stress on yeast cell morphology was assessed by scanning electron microscopy (SEM). In Experiment 1, along the fermentation cycles, strain Y904 showed a decrease in cell viability after sugar concentration of 223 g L−1. SEM images showed that Y904 cells were wrinkled after this cycle. In the case of strain C22, no differences in cell viability were observed along the cycles. However, for both strains, the residual sugars were relatively high and the ethanol content was below the maximum potential. In Experiment 2, for strain Y904, no differences were observed between adapted and non-adapted yeasts in terms of ethanol content, cell viability, and morphology. In the case of strain C22, cell viability and final ethanol content were significantly higher in the adapted yeast, which had cells less damaged by the osmotic stress. In conclusion, the study supports the importance of yeast strain selection and adaptation for efficient VHG fermentation, by demonstrating the superior performance of yeast strain C22 in response to increasing initial sugar content.

Computational mathematical modeling in the cocoa fermentation process in four isolated systems

In the southern region of Bahia, the cocoa culture has been a source of income and moved the economy for a long time, but the emergence of the “witch's broom” (Moniliophthora Perniciosa) caused the decline of this productive sector. Given the importance of cocoa for the region, makes sense to use it as an object of study for the development of academic research that can foster the reheating of this branch of the economy. In this context, for the processing of cocoa to occur to be able to use in the manufacture of chocolate and derivatives it needs to go through 5 distinct stages, being: harvesting, breaking, fermentation, drying, and storage. The stages in question are responsible for more than 45% of the organoleptic properties of cocoa, i.e. affect the final quality of the product. Fermentation is one of the most important stages since it is through fermentation that cocoa develops most of its characteristics, such as color, flavor, and aroma. The step by step of cocoa fermentation is to let the mass ferment, without stirring, until the temperature reaches 32ºC or if it does not reach the ideal temperature, wait to complete 48h. There are cases in which temperatures can be reached between 40ºC to 60ºC. Thus, the idea arose to create a cocoa fermenter model that could increase the efficiency of the fermentation cycle, and boost its scale and quality. Nowadays the process is done manually, requiring the worker to perform the laborious task of monitoring and stirring the cocoa mass at short intervals, over hours. This work compares four fermenter models through the analysis of heat diffusion. The method is theoretical with the help of computer modeling, where the propagation of heat from a source throughout the system filled with a mass of cocoa is evaluated.

Multi-Omics Analysis of the Co-Regulation of Wood Alcohol Accumulation in Baijiu Fermentation

Methanol, also known as wood alcohol, is a common hazardous by-product of alcoholic beverage fermentation and serves as a crucial indicator for assessing the safety of alcoholic beverages. However, the metabolic mechanisms of methanol production during the solid-state fermentation of Chinese Baijiu remain unclear. In this study, we sought to determine the primary stage of methanol production in Chinese Baijiu by measuring the methanol content at different stages of fermentation. High-throughput multi-omics sequencing techniques were employed to elucidate methanol metabolic pathways and associated microorganisms. In addition, a comprehensive analysis incorporating environmental factors and microbial interactions was conducted to explore their combined effects on methanol production. Methanol was predominantly produced during pit fermentation, with the most significant increase observed within the first seven days. Microorganisms such as Pichia kudriavzevii, Byssochlamys spectabilis, Penicillium, and Aspergillus played a regulatory role in methanol content during the first seven days through their involvement in butyrate and methane metabolic pathways and pectin degradation modules. During Baijiu production, various types of molds and yeasts participate in methanol production. Differences in their abundance within fermentation cycles may contribute to variations in methanol content between stages. Lactobacillus accumulated abundantly in the first seven days in each stage, suppressing methanol-metabolizing microorganisms. In addition, the increased acidity resulting from Lactobacillus metabolism may indirectly promote methanol generation.

Efficient conversion of cane molasses into Tremella fuciformis polysaccharides with enhanced bioactivity through repeated batch culture

Tremella fuciformis polysaccharide (TFPS) is a natural mushroom mucopolysaccharide widely used in health foods, medical care, cosmetic and surgical materials. In this study, we developed an efficient strategy for the repeated batch production of highly bioactive TFPS from the agro-industrial residue cane molasses. Cane molasses contained 39.92 % sucrose (w/w), 6.36 % fructose and 3.53 % glucose, all of which could be utilized by T. fuciformis spores, whereas, the TFPS production efficiency only reached 0.74 g/L/d. Corn cobs proved to be the best immobilized carrier that could tightly absorb spores and significantly shorten the fermentation lag period. The average yield of TFPS in eight repeated batch culture was 5.52 g/L with a production efficiency of 2.04 g/L/d. The average fermentation cycle after optimization was reduced by 61.61 % compared with the initial conditions. Compared to glucose as a carbon source, cane molasses significantly increased the proportion of low-molecular-weight TFPS (TFPS-2) in total polysaccharides from 3.54 % to 17.25 % (w/w). Moreover, TFPS-2 exhibited potent antioxidant capacity against four free radicals (O2−, ABTS+, OH, and DPPH). In conclusion, this study lays the foundation for the efficient conversion of cane molasses and production of TFPS with high bioactivity.

Enhancing l-Malic Acid Production in Aspergillus niger via Natural Activation of sthA Gene Expression.

The efficient production of l-malic acid using Aspergillus niger requires overcoming challenges in synthesis efficiency and excessive byproduct buildup. This study addresses these hurdles, improving the activity of NADH-dependent malate dehydrogenase (Mdh) in the early stages of the fermentation process. By employing a constitutive promoter to express the Escherichia coli sthA responsible for the transfer of reducing equivalents between NAD(H) and NADP(H) in A. niger, the l-malic acid production was significantly elevated. However, this resulted in conidiation defects of A. niger, limiting industrial viability. To mitigate this, we discovered and utilized the PmfsA promoter, enabling the specific expression of sthA during the fermentation stage. This conditional expression strain showed similar phenotypes to its parent strain while exhibiting exceptional performance in a 5 L fermenter. Notably, it achieved a 65.5% increase in productivity, reduced fermentation cycle by 1.5 days, and lowered succinic acid by 76.2%. This work marks a promising advancement in industrial l-malic acid synthesis via biological fermentation, showcasing the potential of synthetic biology in A. niger for broader applications.

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

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.

Method of determining volume yield of biogas during experimental research in biogas technologies

The article deals with the issue of determining the volume of biogas produced during experimental studies during the entire cycle of anaerobic fermentation of organic matter in biogas reactors. The design of the device for determining the volume of biogas produced during the period of the complete cycle of anaerobic fermentation of organic matter in biogas reactors is proposed and given. The use of the proposed device is aimed at both small and large biogas plants, in laboratory conditions and at production facilities. Mathematical dependences are presented, which allow to calculate the volume of biogas determined by the device given in the work. The results of the study of the device using 3D modeling in the Solidworks application program in the Flow Simulation package are presented. The result of the 3D modeling is the graphical dependence of the pressure distribution in the tubes of the measuring device, namely the gas pipeline and the Pitot tube, with the subsequent establishment of the amount of biogas passed through the measuring device in a certain time interval. The work noted a high convergence of the comparative analysis of the data obtained during 3D modeling and calculated analytically. Considered in the article, the main issues of the proposed method of determining the produced volume of biogas during experimental research will allow to increase the accuracy of the research work of scientists, organizations and enterprises in the field of biogas technologies and registration of the produced volume of biogas.