Mixed Fermentation Research Articles

Evaluation of physiochemical composition, phenolic compounds, and antioxidant activity of Kombucha produced from Thunbergia laurifolia as a potential functional food

SummaryKombucha has gained global attention for its beneficial bioactive compounds. This study aimed to evaluate Thunbergia laurifolia tea as a potential substrate for Kombucha production due to its rich polyphenol content and biological properties, including antioxidant and anticancer properties, through monoculture and simultaneous mixed coculture fermentation. The pH and brix of the teas decreased significantly during fermentation, indicating sugar hydrolysis and organic acid synthesis by fermenting microbes. The alcohol content was higher in yeast monocultures (45.80 ± 0.00¬50.23 ± 0.08 g L−1) compared to mixed coculture fermented (CBY) tea (20.16 ± 0.00 g L−1). Total phenolic and flavonoid contents and antioxidant activity increased significantly in CBY tea compared to non‐fermented and monoculture teas. CBY also exhibited the highest cumulative phenolic compound content, including rosmarinic acid, caffeic acid, gallic acid, rutin, catechin, and quercetin, compared to monoculture teas. Overall, Thunbergia laurifolia tea shows promise as a substrate for kombucha production, with improved bioactive constituents and antioxidant activity.

Precursors consumption preferences and thiol release capacity of the wine yeasts Saccharomyces cerevisiae, Torulaspora delbrueckii, and Lachancea thermotolerans

The aromatic profile of wine determines its overall final quality, and among the volatile molecules that define it, varietal thiols are responsible for shaping the distinctive character of certain wine varieties. In grape must, these thiols are conjugated to amino acids or small peptides in a non-volatile form. During wine fermentation, yeasts play a principal role in expressing these aromatic compounds as they internalise and cleavage these precursors, releasing the corresponding free and aroma-impacting fraction. Here, we investigate the impact of three wine yeasts (Saccharomyces cerevisiae, Torulaspora delbrueckii and Lachancea thermotolerans) on thiol releasing in synthetic grape must fermentations supplemented with different cysteinylated (Cys-4MSP and Cys-3SH) and glutathionylated (GSH-4MSP and GSH-3SH) precursors. We demonstrate higher consumption levels of cysteinylated precursors, and consequently, higher amounts of thiols are released from them compared to glutathionylated ones. We also report a significant impact of yeast inoculated on the final thiols released. Meanwhile T. delkbrueckii exhibits a great 3SHA releasing capacity, L. thermotolerans stands out because of its high 3SH release. We also highlight the synergic effect of the co-inoculation strategy, especially relevant in the case of S. cerevisiae and L. thermotolerans mixed fermentation, that has an outstanding release of 4MSP thiol. Although our results stem from a specific experimental approach that differs from real winemaking situations, these findings reveal the potential of unravelling the specific role of different yeast species, thiol precursors and their interaction, to improve wine production processes in the context of wine aroma enhancement.

Using pre-fermented sugar beet pulp as a growth medium to produce Pleurotus ostreatus mycelium for meat alternatives

This study aimed to determine the compatibility of pre-fermented sugar beet pulp to support the growth of Pleurotus ostreatus mycelium in submerged fermentation. The goal was to create a meat alternative based on mycelial-fermented pulp. It was further explored whether pre-fermentation with lactic acid bacteria (LAB) on the pulp increased meat-like properties, such as aroma, springiness, and hardness, in the final product. Three strains were selected from a high throughput screening of 105 plant-derived LAB based on their acidification and metabolite production in the pulp. Two homofermentative strains (Lactococcus lactis) and one heterofermentative strain (Levilactobacillus brevis) were selected based on their low ethanol production, high lactic acid production, and overall acidification of the pulp. Mycelium of P. ostreatus was grown in submerged fermentations on the pre-fermented pulp, and the biomass was removed by centrifugation. The fungal strain consumed all available sugars and acids and released arabinose to the media. Volatiles were detected using GC–MS, and a large increase in concentrations of hexanal, 1-octen-3-ol, and 2-octenal was measured. Concentration of 1-octen-3-ol was lower in the pre-fermented samples vs. the non-pre-fermented. LC-MS amino acid analysis showed the presence of all essential amino acids on day 0 and 7 of fermentation. The highest concentration of amino acids was for glutamic acid/glutamine and aspartic acid/asparagine. A decrease in all amino acids after 7 days of fungal fermentation was measured for all fermentations. The decrease was more significant for pre-fermented samples. This was also confirmed through a total protein determination, except for samples pre-fermented with Lactococcus lactis strain NFICC142 which increased in total protein content after fungal fermentation. The protein digestibility increased after fungal fermentation, and the highest increase was seen for non-pre-fermented samples. The springiness of the fermented product indicated similarities to meat alternatives, while the hardness was much lower than other meat alternatives. The results indicate that dried sugar beet pulp can be used for submerged cultivation of P. ostreatus, but that pre-fermentation does not improve the physical or nutritional properties of the end product significantly, except for an increased protein content for NFICC142 pre-fermented media. This is the first known attempt to use LAB and P. ostreatus in mixed fermentation to produce fungal mycelium, as well as the first attempt at using SBP in a liquid fermentation for mycelial production of P. ostreatus.

Protective effects of Chinese bayberry pomace wine against oxidative stress on Drosophila melanogaster

The Chinese bayberry pomace wine (CPW) was prepared with the assisted fermentation of lactic acid bacteria and acetic acid bacteria, and its antioxidant effect on Drosophila melanogaster was researched. After mixed fermentation, CPW had a better color, which means there was more retention of anthocyanins, and the functional activity of anthocyanins could enhance the antioxidant capacity of flies. We found that the lifespan of flies exposed to CPW was prolonged, and the reproductive capacity of these flies was decreased. The food intake of flies was also influenced by CPW with gender differences. Furthermore, CPW alleviated the excessive proliferation of the intestinal precursor cells of H2O2-induced flies and activated the transcription level of antibacterial peptide genes. CPW had a protective effect on H2O2-induced acute injury flies, with an increased survival rate, enhanced SOD and CAT activities, and decreased malondialdehyde (MDA) content in flies. The expression of oxidative stress-related genes including CuZn-SOD, Mn-SOD, and CAT was also significantly upregulated by CPW, but the downregulation effect of CPW on age-related gene expression such as methuselah (MTH), the target of rapamycin (TOR) and ribosomaiprotein S6 kinase (S6K) was sex-specific. These results suggested that CPW played an important role in anti-oxidative stress injury, which was beneficial to promoting the reuse of by-products from Chinese bayberry processing.

Mixed culture fermentation using Lactobacillus delbrueckii and novel Lactiplantibacillus plantarum strains isolated from traditional chhurpi from Sikkim Himalayan region for potential probiotic and improved functional properties

The aim of the study was to isolate potential probiotic lactic acid bacteria (LAB) strains from the traditional fermented milk products, Chhurpi of the Sikkim Himalayan region and to prepare curd using mixed culture fermentation. A preliminary probiotic assessment of 110 LAB isolates including antimicrobial activity, bile and acid tolerance, surface hydrophobicity, auto-aggregation and co-aggregation, and adhesion to Caco-2 cells, was performed. Lactiplantibacillus plantarum strains N4, CHDE2, CHDE4, and SS22 demonstrated better viability in bile (0.3%) and acid (pH 2.5), adherence with hydrophobicity (13.93–92.85%), auto-aggregation (72.44–89.74%), adhesion to Caco-2 cells (45–73.61%) and antimicrobial activity against food borne pathogens. These strains were used for mixed culture fermentation with a previously screened curd forming strain Lactobacillus delbrueckii WS4. Curd produced using mixed culture fermentation of Lb. delbrueckii WS4 and the selected Lp. plantarum strains had a relatively higher acid production (pH 3.97–4.01), protein hydrolysis, and antioxidant activity. Further, mixed culture fermentation also resulted in the increase of HOCl scavenging activity (12.22–32.96%), myeloperoxidase (MPO) inhibition activity (22.38–42.94%) and angiotensin converting enzyme (ACE) inhibition (15.61–33.03%) as compared to that of WS4 fermentation (P < 0.05). This is the first report on identification of potential probiotic strains from the traditional fermented milk products of Sikkim and application in mixed culture fermentation with enhanced multifunctional potential.

Repercussions of Lactiplantibacillus plantarum HYY‐DB9 and Levilactobacillus brevis GIM 1.773 on the degradation of nitrite, volatile compounds, and sensory assessment of traditional Chinese paocai

SummaryPaocai, as one of the most widely consumed traditional fermented foods in China, is dominated by lactic acid bacteria (LAB), which exert a significant influence on the dynamics of metabolites, microecological changes, and sensory quality. In this study, five different paocai groups were designed for fermentation using Lactiplantibacillus plantarum HYY‐DB9 (LP), Levilactobacillus brevis GIM 1.773 (LB), a mixture of two LABs (LP + LB), pasteurisation (PST), and natural fermentation (NF). Nitrite content, pH, titratable acidity, viable cell counts (LAB and yeasts), metabolites (organic acids and volatile substances), and sensory evaluation were determined for each group. The results demonstrated that the mixed fermentation with two LABs (LP + LB) significantly reduced nitrite content. Organic acids produced by LAB played a crucial role in the degradation process, particularly lactic acid which exhibited the most pronounced effect on nitrite degradation. Furthermore, artificial inoculation of LAB fermentation resulted in improved taste and flavour of paocai along with increased production of alcohols, esters, and acids compared to traditional natural fermentation. These findings have important implications for enhancing paocai quality control and managing nitrite content while also providing an excellent fermentation agent for fermented paocai.

Impact of different lactic acid bacteria on nitrite degradation and quality of fermented carrot

SummaryIn this study, six groups of carrots were designed and fermented using Weissella paramensenteroides MbWp142 (WP), Levilactobacillus brevis GDMCC 1.773 (LS), Leuconostoc mesenteroides GDMCC 1.774 (SE), mixed fermentation of three lactic acid bacteria (WP + LS + SE), pasteurisation group (BG) and natural fermentation group (CK). GC–MS results indicated that inoculation of WP + LS + SE increased the types and contents of flavour substances such as alcohols, esters and hydrocarbons. Compared with other experimental groups, the peak nitrite value in the LS group was lower due to the production of organic acids by lactic acid bacteria. Sensory evaluation revealed that the quality and flavour of carrot fermented by LS were superior to those fermented by SE, WP and WP + LS + SE. Therefore, Levilactobacillus brevis used as a starter for fermenting carrot can enhance product quality and reduce nitrite accumulation during fermentation.

Mechanisms of single and mixed microbial fermentation to improve summer-autumn green tea

To investigate the effect of individual and collaborative fermentation on summer-autumn green tea (SAGT) quality. Liquid fermentation with individual inoculation of Aspergillus cristatus (ACFT), Aspergillus niger (ANFT) and mixed inoculation of A. cristatus/A. niger (MFT), respectively, with SAGT extracts (CT) as raw materials. The volatile organic compounds (VOCs), characteristic non-volatile compounds and sensory evaluation of tea samples were determined. The results showed a significant decrease in the content of tea polyphenols, carbohydrates and nongalloylated catechins (C, EC) and a significant increase in the amount of VOCs in MFT compared to ANFT and ACFT. The results of metabolic pathway analysis and sensory evaluation showed that ACFT went through the terpene and phenylpropanoic acid metabolic pathway, which produced large amounts of α-terpineol, phenethyl alcohol, and methyl salicylate, which in turn conferred ACFT with distinctly sweet, floral, and herbal aroma. ANFT produces large amounts of linalool oxides I and II, mainly through the linalool oxide metabolic pathway, making ANFT a distinctive aged and woody aroma. MFT may be due to the strong woody aroma of linalool oxides masking other weaker and better aromas, thus giving MFT a significant woody, herbal and stale aroma. This study provides new insights and a theoretical basis for mixed fungal fermentation to improve the quality of SAGT.

The impact of simultaneous inoculation with Torulaspora delbrueckii and Hanseniaspora uvarum combined with Saccharomyces cerevisiae on chemical and sensory quality of Sauvignon blanc wines.

Non-Saccharomyces yeasts have great potential in improving wine quality, showing personality characteristics, and highlighting the terroir of wine. In this study, we evaluated the impact of simultaneous inoculation with the non-Saccharomyces yeasts Torulaspora delbrueckii or (and) Hanseniaspora uvarum in combination with Saccharomyces cerevisiae (EC1118 or VL3) on the aromatic compounds and sensory quality of Sauvignon blanc wines. The growth of yeast groups in the alcoholic fermentation process was tracked using fluorescence in situ hybridization. The presence of non-Saccharomyces yeast notably impacted the distribution of S. cerevisiae and was related to the species of yeast. The co-fermentation of H. uvarum and S. cerevisiae improved the content of total esters, especially acetate esters. Simultaneous inoculation of T. delbrueckii or (and) H. uvarum significantly increased the content of total terpenes, especially linalool. Similar results were found for some higher alcohols and organic acids. Sensory evaluation showed that the wines mixed fermentation with H. uvarum had significantly tropical fruit aroma characteristics. Citrus and mineral notes, typical aroma characteristics of Sauvignon blanc wine, were enhanced by mixed fermentation strategies with T. delbrueckii or (and) H. uvarum and different S. cerevisiae. Hence, co-fermentation by T. delbrueckii or H. uvarum combined with S. cerevisiae could significantly improve the sensory quality of Sauvignon blanc wine.

FhlA is a Formate Binding Protein.

Escherichia coli uses glycolysis and mixed acid fermentation and produces formate as by product. One system E. coli uses for formate oxidation is formate hydrogen lyase complex (FHL). The expression of the FHL complex is dependent on formate and regulated by the transcriptional regulator FhlA. The structure of FhlA is composed of three domains. The N-terminal domain is putatively responsible for formate binding and FhlA oligomerization as a tetramer, the central portion of FhlA contains a AAA+ domain that hydrolyzes ATP, and the C-terminal domain binds DNA. Formate enhances FhlA-mediated expression of FHL; however, FhlA direct interaction with formate has never been demonstrated. Formate-protein interactions are challenging to assess, due to the small and ubiquitous nature of the molecule. Here, we have developed three techniques to assess formate-protein interaction. We use these techniques to confirm that FhlA binds formate in the N-terminal domain in vitro, and that this interaction is partially dependent on residues E183 and E363, consistent with previous reports. This study is a proof of concept that these techniques can be used to assess other formate-protein interactions.

Cheese Whey Protein and Blueberry Juice Mixed Fermentation Enhance the Freeze-Resistance of Lactic Acid Bacteria in the Freeze-Drying Process.

The effects of MRS, whey protein and blueberry alone, and mixed fermentation on the survival rate of lactic acid bacteria under various freeze-drying conditions were investigated. The surface structure of the freeze-dried powders was also investigated to explore the anti-freezing protection mechanism of mixed whey protein and blueberry fermentation on the bacteria. It was found that the mixed fermentation medium of blueberry and whey protein has a protective effect on the freeze-drying bacteria and is better than the traditional MRS and whey protein medium. The optimal concentration of blueberry juice addition was 9%. The survival rate of the pre-freezing temperature at -80 °C was higher than at -20 °C after the pre-freezing and freeze-drying processes. The freeze-drying thickness of 0.3 cm could improve the survival rate of the bacteria. The Fourier transform infrared spectroscopy results indicated the interaction between the whey protein, anthocyanins, and the surface composition of the lactic acid bacteria.

Effect of Mixed Cultures on Microbiological Development in Berliner Weisse Beer

Sour beers play an important role in the brewing market, and their production has been growing exponentially. In light of this, six microorganisms directly related to this class of beer were studied, and the fermentation behavior of six strains used in the past for traditional commercial Berliner Weisse beer production was monitored. The microorganisms used were Lactobacillus brevis, Lactobacillus parabrevis, Brettanomyces bruxellensis, and Brettanomyces anomalus and two strains of Saccharomyces cerevisiae. The six microorganisms were selected in a previous work, and a comparison between single and mixed fermentations was carried out via daily measurements of the fermentation parameters like pH, extract, and cell count during 22 days. The ability to isolate a specific microorganism from a mixed culture was investigated using three commonly used nutrient media and aerobic/anaerobic growth conditions. Both Lactobacillus and Brettanomyces could be isolated; however, the conditions imposed were not sufficient in order to isolate Saccharomyces. Fermentations carried out with LAB and Brettanomyces showed a decrease in Lactobacillus growth if compared to pure fermentations, but no influence on the growth of Brettanomyces could be perceived. In general, fermentations carried out in the presence of Saccharomyces were dominated by this yeast. Its quick growth seems to be responsible for the high end pH values observed as well as the decrease in cell growth for both LAB and Brettanomyces. A decrease in the cell viability of Saccharomyces was followed by an increased growth of the other microorganisms involved, possibly meaning that the molecules released through apoptosis are used by both LAB and Brettanomyces as a valuable nutrient source. The volatile compound concentrations of the first group were higher in fermentations with Saccharomyces, whereas esters’ concentration was higher in fermentations carried out only with Brettanomyces and Lactobacillus. Furthermore, understanding how these microorganisms interact during the fermentation process can help brewers better control production and ensure the consistency in the quality of the final product. The end pH values and acidity reached levels acceptable for Berliner Weisse beer. This innovative approach certainly contributes to the evolution and refinement of the art of brewing.

Optimising butyric and lactic acid yield from xylose by adjusting pH

This work studies the pH effect in xylose mixed culture fermentation, focusing on lactic and butyric acid production. Batch tests showed a complete substrate consumption at slightly acidic (pH 6) and alkaline conditions (pH 8), but a great inhibition of xylose conversion was observed at pH 4. Acetic acid was the only product at pH 8, while at pH 6, butyric and propionic acids were quantified as well with a large proportion of unidentified compounds. Continuous reactor operation showed that changes within the acidic pH range (pH 4.5 to pH 6) affect the acidification degree but not the product distribution, reaching the maximum butyric acid yield (0.38 Cmol/Cmol-s) at pH 5, while lactic acid was only detected when xylose conversion or butyric acid concentration dropped. Batch tests demonstrated that butyric acid was not inhibitory for xylose or lactic acid conversion and that the main product of lactic acid fermentation was butyric acid. Although pH is an essential variable steering the fermentation yield and selectivity, this study demonstrates that it must be combined with other operational conditions in order to obtain a stable production of lactic and butyric acids.

Effect of cultures of synthetic starters on the flavour and ethyl carbamate content of rice wine

SummaryEthyl carbamate (EC) concentration is an important indicator of the safety of rice wine. In this study, the effects of replacing traditional starters with synthetic starters on the quality of rice wine were studied to provide a basis for the application of laboratory strains to explore the metabolic basis of EC formation in rice wine fermentation systems. The effects of synthetic starters on the physicochemical indices, free amino acids, flavour compounds, urea and EC of rice wine were studied. The results showed that the microorganism species and inoculation fermentation method strongly influenced the physicochemical and flavour properties of the rice wine, among which continuous co‐fermentation improved the mellowness and flavour of the rice wine. The concentrations of urea and EC in rice wine fermented with synthetic starters decreased significantly compared with those in the control group, in which the urea content decreased by up to 97.4% and the EC content decreased by up to 90.9%. In addition, the flavour compound data showed that the differences in the aromas of rice wine fermented with different starters were mainly due to the differences in the contents of alcohols and esters. These findings suggest that EC can be regulated by changes in starters and provide guidance for the optimal configuration of mixed fermentation systems.

Hybrid pathway of bio-ethanol production employing empty fruit bunches co-gasified with charcoal and mixed culture fermentation: Optimization using response surface methodology

The research focuses on the synthesis of syngas from lignocellulosic biomass via co-gasification, employing response surface methodology. In addition, the study aims to optimize syngas fermentation efficiency for bioethanol production, utilizing two species of microorganisms – Saccharomyces cerevisiae and Clostridium butyricum – within an integrated biorefinery framework. The raw syngas was generated through the co-gasification of empty fruit bunches and charcoal mixtures (75:25). The optimal ratio of these components was determined via central composite design. The individual performances of S. cerevisiae and C. butyricum, as well as their co-fermentation, were thoroughly investigated, considering parameters such as colony forming units (CFU), pH, total organic carbon (TOC), and syngas flow rate. Morphological features of microorganisms during syngas fermentation were characterized using field emission scanning electron microscopy analysis. The results indicated that the highest bioethanol concentration, reaching 31.20 mmol, was achieved through co-fermentation as opposed to single-inoculum fermentation. Furthermore, a significant increase (3.08%) in bioethanol productivity was observed when the syngas flow rate was elevated from 50 to 1000 mL/min. Therefore, microbial co-fermentation emerges as a promising strategy to enhance bioethanol production from syngas derived from lignocellulosic biomass. Highlights Parametric optimization for co-gasification using response surface methodology Syngas was co-fermented using Saccharomyces cerevisiae and Clostridium butyricum Effects of syngas (CFU, pH, and TOC) were investigated during co-fermentation Bioethanol production increased 3.08% when syngas flowrate increased from (50 to 1000 mL/min)

Comparative Evaluation of Flavor and Sensory Quality of Coffee Pulp Wines.

Coffee pulp wines were produced through the mixed fermentation of Saccharomyces cerevisiae, and the flavor and sensory characteristics were comparatively evaluated. A total of 87 volatile components were identified from five coffee pulp wines, of which 68 were present in all samples, accounting for over 99% of the total concentration. The sample fermented contained significantly higher levels of volatile metabolites (56.80 mg/g). Alcohols (22 species) and esters (26 species) were the main flavor components, with the contents accounting for 56.45 ± 3.93% and 31.18 ± 4.24%, respectively, of the total. Furthermore, 14 characteristic components were identified as potential odor-active compounds, contributing to sweet and floral apple brandy flavor. Although the characteristic components are similar, the difference in the content makes the overall sensory evaluation of the samples different. The samples formed by fermentation of four strains, which obtained the highest score (86.46 ± 0.36) in sensory evaluation, were further interpreted and demonstrated through the Mantel test. The results of the component analysis were effectively distinguished by OPLS-DA and PCA, and this validation was supported by sensory evaluation. The research results provided a technical reference for the production of coffee pulp wines.

Dynamic changes in aromas and precursors of edible fungi juice: mixed lactic acid bacteria fermentation enhances flavor characteristics.

Lactic acid bacteria (LAB) fermentation technology has been increasingly used in the deep processing of edible fungi. However, the flavor profiles of edible fungi products after mixed LAB fermentation have received less attention and how aromas changes during the mixed LAB fermentation are still open questions. In the present study, fermented Hericium erinaceus and Tremella fuciformis compound juice (FHTJ) was prepared by mixed LAB strains. We aimed to systematically monitor the dynamic changes of aromas and precursors throughout the fermentation process and a data-driven association network analysis was used to tentatively illustrate the mechanisms of formation between aromas and their precursors. Mixed LAB fermentation could enrich the aroma profile of FHTJ, reducing the unpleasant flavors such as nonanal and 1-octen-3-ol, as well as increasing the floral flavors such as ethyl acetate and α-pinene. Partial least squares-discriminant analysis and relative odor activity values revealed that 11 volatile chemicals were recognized as aroma-active markers. Volcano plot analysis showed that 3-octen-2-one (green flavor) was the key aroma-active marker in each stage, which was down-regulated in fermentation stages I, II and IV, whereas it was up-regulated in stage III. 3-Octen-2-one was significantly negatively correlated with organic acids, particularly pyruvate (r2 = -0.89). Ethyl caprylate (floral flavor) was up-regulated in the late fermentation stage, and showed a negative correlation with sugar alcohols and a positive correlation with organic acids, especially tartaric acid (r2 = 0.96). The present study demonstrates the beneficial effect of mixed LAB fermentation on flavor characteristics, providing guidance for fermented edible fungi juice flavor quality monitoring and control. © 2024 Society of Chemical Industry.

The fuel property and application prospect of water-containing biofuel from Clostridium acetobutylicum fermentation products

Biobutanol, a promising green alternative fuel, fermented from Clostridium acetobutylicum, while its high-cost and limited yield constraining its development. ABE (acetone-butanol-ethanol) and IBE (isopropanol-butanol-ethanol) are mixed fermentation products from non-edible biomass raw materials, using them together with water as alternative fuels will reduce industrial production costs and save fossil fuels. Therefore, this study conducted a multifaceted experimental evaluation on ABE/IBE mixed fuels with different water content, demonstrating that it has good water holding capacity when mixed with traditional fossil fuels. Taking ABE (3: 6: 1) as an example, its water holding capacity after mixing with diesel at 10–90 % is 0.37–7.83 % at 20 °C. Meanwhile, the particle size of ABE/IBE mixed fuels is about 2–30 nm, exhibiting a microemulsion with thermodynamic stability. The anhydrous or water-containing mixed fuel with the ratio of ABE (IBE) of 10%–50 % meets the range of the density and kinematic viscosity of diesel engine fuel. The mixed fuel is non-corrosive to copper without water, and a water content of about 3 % or higher will increase the risk of engine corrosion at 20 °C. Despite the addition of biofuel and water, studies on energy combustion performance and pollutant emission performance have found that appropriate addition of biofuel and water can produce higher power output and lower pollutant emissions than traditional fossil fuels, with ABE20W0.5 being the optimal. This study demonstrates the great potential of ABE and IBE as biofuels to achieve carbon neutrality goals, providing novel research direction for green alternative fuels in the future.

Liquid Phase Parameter Analysis of Methanogenesis in Anaerobic Digestion of Coal Promoted by Kitchen Waste

In order to study the effect of food and kitchen waste on promoting methane production by collaborative fermentation of coal, this paper selected lignite and food and kitchen waste as the research objects, and carried out the gas production experiment of mixed fermentation of coal and food and kitchen waste with different ratios at 35 ℃ with mine water as the bacteria source. The results showed that the cumulative CH4 production was the highest in the mixed fermentation with the ratio of 1:4 (coal: kitchen waste). Therefore, exploring the optimal mixture ratio of coal and food waste fermentation can not only effectively improve the gas production effect, but also broaden the diversified utilization ways of coal and food waste, which has a good development potential.

Metagenome-assembled genomes provide insight into the metabolic potential during early production of Hydraulic Fracturing Test Site 2 in the Delaware Basin.

Demand for natural gas continues to climb in the United States, having reached a record monthly high of 104.9 billion cubic feet per day (Bcf/d) in November 2023. Hydraulic fracturing, a technique used to extract natural gas and oil from deep underground reservoirs, involves injecting large volumes of fluid, proppant, and chemical additives into shale units. This is followed by a "shut-in" period, during which the fracture fluid remains pressurized in the well for several weeks. The microbial processes that occur within the reservoir during this shut-in period are not well understood; yet, these reactions may significantly impact the structural integrity and overall recovery of oil and gas from the well. To shed light on this critical phase, we conducted an analysis of both pre-shut-in material alongside production fluid collected throughout the initial production phase at the Hydraulic Fracturing Test Site 2 (HFTS 2) located in the prolific Wolfcamp formation within the Permian Delaware Basin of west Texas, USA. Specifically, we aimed to assess the microbial ecology and functional potential of the microbial community during this crucial time frame. Prior analysis of 16S rRNA sequencing data through the first 35 days of production revealed a strong selection for a Clostridia species corresponding to a significant decrease in microbial diversity. Here, we performed a metagenomic analysis of produced water sampled on Day 33 of production. This analysis yielded three high-quality metagenome-assembled genomes (MAGs), one of which was a Clostridia draft genome closely related to the recently classified Petromonas tenebris. This draft genome likely represents the dominant Clostridia species observed in our 16S rRNA profile. Annotation of the MAGs revealed the presence of genes involved in critical metabolic processes, including thiosulfate reduction, mixed acid fermentation, and biofilm formation. These findings suggest that this microbial community has the potential to contribute to well souring, biocorrosion, and biofouling within the reservoir. Our research provides unique insights into the early stages of production in one of the most prolific unconventional plays in the United States, with important implications for well management and energy recovery.