Search Results (471)

To achieve energy transition, hydrogen and carboxylic acids have attracted much attention due to their cleanliness and renewability. Anaerobic fermentation technology is an effective combination of waste biomass resource utilization and renewable energy development. Therefore, the utilization of anaerobic fermentation technology is expected to achieve efficient co-production of hydrogen and carboxylic acids. However, this process is fundamentally affected by gas–liquid mass transfer kinetics, bubble behaviors, and system partial pressure. Moreover, the related studies are few and unfocused, and no systematic research has been developed yet. This review systematically summarizes and discusses the basic mathematical models used for gas–liquid mass transfer kinetics, the relationship between gas solubility and mass transfer, and the liquid-phase product composition. The review analyzes the roles of the headspace gas composition and partial pressure of the reaction system in regulating co-production. Additionally, we discuss strategies to optimize the metabolic pathways by modulating the gas composition and partial pressure. Finally, the feasibility of and prospects for the realization of hydrogen and carboxylic acid co-production in anaerobic fermentation systems are outlined. By exploring information related to gas mass transfer and system pressure, this review will surely provide an important reference for promoting cleaner production of sustainable energy. Full article

The fermentation of Actinobacillus succinogenes in bioelectrochemical systems offers a promising approach to enhance biotechnological succinate production by shifting the redox balance towards succinate and simultaneously enabling CO₂ utilization. Key process parameters include the applied electric potential, electrode material, and reactor design. This study investigates the influence of various carbon fabric electrodes and applied potentials on product distribution during fermentation of A. succinogenes. Building on prior findings that potentials between −600 mV and –800 mV increase succinate production, recent data reveal that more negative potentials, beyond the water electrolysis threshold, trigger electrochemical side reactions, altering product yields. Specifically, succinate decreased from 19.76 ± 0.41 g∙L⁻¹ to 14.1 ± 1.6 g∙L⁻¹, while lactate rose from 0.59 ± 0.12 g∙L⁻¹ to 3.12 ± 0.21 g∙L⁻¹. Contrary to common assumptions, the shift is not primarily driven by oxygen formation. Instead, the results indicate that the intracellular redox potential is affected by both the applied potential and hydrogen evolution, which alters metabolic pathways to maintain redox balance. These findings demonstrate that more negative applied potentials in electro-fermentation processes can impair succinate yields, emphasizing the importance of fine-tuning electrochemical conditions in the system for optimized biotechnological succinate production. Full article

Despite being recognized as toxic in anaerobic systems, sulfide’s potential to enhance hydrogen fermentation via microbial modulation remains underexplored. This study evaluated the combined effects of sulfide concentration (0–800 mg S/L) and heat pretreatment on hydrogen production during dark fermentation (DF). Without pretreatment, hydrogen yield reached 83 ± 2 mL/g COD at 0 mg S/L but declined with increasing sulfide, becoming negligible at 800 mg S/L. In contrast, heat-pretreated inocula showed markedly improved performance: peak cumulative production (4628 ± 17 mL) and yield (231 ± 1 mL/g COD) were attained at 200 mg S/L, while the maximum production rate (1462 ± 64 mL/h) occurred at 400 mg S/L. These enhancements coincided with elevated acetic and butyric acids, indicating a metabolic shift toward hydrogen-producing pathways. The microbial analysis of heat-pretreated samples revealed an enrichment of Clostridium butyricum (from 73.1% to 87.5%) and Clostridium perfringens, which peaked at 13.5% at 400 mg S/L. This species contributed to butyric acid synthesis. At 800 mg S/L, Clostridium perfringens declined sharply to 0.6%, while non-hydrogenogenic Levilinea saccharolytica proliferated, correlating with reduced butyric acid and hydrogen output. These findings indicate that sulfide supplementation, when combined with heat pretreatment, selectively restructures microbial communities and metabolic pathways, enhancing DF performance. Full article

Odors from pet cats can negatively affect the quality of life of cat owners. The diverse bioactive compounds in plant extracts make them a promising candidate for effective odor reduction. This study evaluated twelve plant extracts for deodorizing efficacy via in vitro fermentation tests. Rosemary extract and licorice extract exhibited better deodorizing effects, with fractions of rosemary extract below 100 Da demonstrating the most effective deodorizing performance. Based on these findings, subsequent feeding trials were conducted using rosemary extract and its fractions below 100 Da. In the feeding trial, adult British Shorthair cats were divided into three groups (Control Check, RE, and RE100) and housed in a controlled-environment respiration chamber for 30 days. Measurements included odor emissions, fecal and blood physicochemical parameters, immune parameters, microbiota composition based on 16S rRNA sequencing, and metabolome analysis. The results of the feeding trial indicated that rosemary extract significantly reduced ammonia and hydrogen sulfide emissions (46.84%, 41.64%), while fractions below 100 Da of rosemary extract achieved even greater reductions (55.62%, 53.87%). Rosemary extract regulated the intestinal microbial community, significantly increasing the relative abundance of the intestinal probiotic Bifidobacterium (p < 0.05) and reducing the population of sulfate-reducing bacteria (p < 0.05). It also significantly reduced urease and uricase activities (p < 0.05) to reduce ammonia production and inhibited the degradation of sulfur-containing proteins and sulfate reduction to reduce hydrogen sulfide emissions. Furthermore, rosemary extract significantly enhanced the immune function of British Shorthair cats (p < 0.05). This study suggests that rosemary extract, particularly its fractions below 100 Da, is a highly promising pet deodorizer. Full article

The robust structure of algal cell walls presents a major barrier in the recovery of fermentable sugars and intracellular lipids for biofuel production. This study investigates the effectiveness of ultraviolet (UV) radiation and UV-assisted hydrogen peroxide (UV/H₂O₂) pretreatment on a local mixed marine algal culture to enhance biofuel production through cell wall disruption. Local mixed cultures of marine microalgae (LMCMA) were pretreated with UV for various exposure times (5–30 min) and with UV/H₂O₂ using H₂O₂ concentrations ranging from 0.88 to 3.53 mM. The impact of pretreatment was evaluated based on morphological changes (SEM and TEM), elemental composition (C, H, N), sugar release, and downstream fermentation yields of ethanol, methanol, 1-propanol, 1-butanol, and 1-pentanol using Saccharomyces cerevisiae. UV pretreatment at 20–30 min yielded the highest carbohydrate release (up to 0.025 g/gDCW), while UV/H₂O₂ at 1.76 mM achieved maximum sugar liberation (0.0411 g/gDCW). Fermentation performance was enhanced under optimized conditions, with peak ethanol yields of 0.3668 g ethanol/g carbohydrates (UV, 30 min, 48 h) and 0.251 g ethanol/g (UV/H₂O₂, 0.88 mM, 24 h). This study also demonstrated selective production of higher alcohols under varying fermentation temperatures (30–37 °C). These findings highlight the potential of combining oxidative pretreatment and process optimization to enhance biofuel recovery from environmentally relevant algal biomass. Full article

Adequate treatment of the organic fraction of municipal solid waste (OFMSW) in co-digestion with sewage sludge (SS) through dark fermentation (DF) technologies has been widely studied and recognized. However, there is little experience with a high-solids approach, where practical and scalable conditions are established to lay the groundwork for further development of feasible industrial-scale projects. In this study, the biochemical hydrogen potential of OFMSW using a 7 L batch reactor at mesophilic conditions was evaluated. Parameters such as pH, redox potential, temperature, alkalinity, total solids, and substrate/inoculum ratio were adjusted and monitored. Biogas composition was analyzed by gas chromatography. The microbial characterization of SS and post-reaction percolate liquids was determined through metagenomics analyses. Results show a biohydrogen yield of 38.4 NmLH₂/gVS OFMSW, which forms ~60% of the produced biogas. Aeration was proven to be an efficient inoculum pretreatment method, mainly to decrease the levels of methanogenic archaea and metabolic competition, and at the same time maintain the required total solid (TS) contents for high-solids conditions. The microbial community analysis reveals that biohydrogen production was carried out by specific anaerobic and aerobic bacteria, predominantly dominated by the phylum Firmicutes, including the genus Bacillus (44.63% of the total microbial community), Clostridium, Romboutsia, and the phylum Proteobacteria, with the genus Proteus. Full article

Deep learning has great potential in the field of functional peptide prediction. This study combines metagenomics and deep learning to efficiently discover potential umami peptides in fermented sausages. A candidate peptide library was generated using metagenomic data from fermented sausages, an integrated deep learning model was constructed for prediction, and SHAP (SHapley Additive exPlanations) interpretability analysis was performed to elucidate the key amino acid features and contributions of the model in predicting umami peptides, screening the top ten peptides with the highest predicted probability. Subsequently, molecular docking was performed to assess the binding stability of these peptides with the umami receptor T1R1/T1R3, selecting the three peptides DDSMAATGL, DGEEDASM, and DEEEVDI with the most stable binding for further study. Docking analysis revealed the important roles of the key receptor residues Glu301, Arg277, Lys328, and His71 in hydrogen bond formation. Molecular dynamics simulations validated the robust integrity of the peptide–receptor associations. Finally, sensory evaluation demonstrated that these three peptides possessed significant umami characteristics, with low umami thresholds (0.11, 0.37, and 0.44 mg/mL, respectively). This study, based on metagenomics and deep learning, provides a high-throughput strategy for the discovery and validation of functional peptides. Full article

This study reports the effects of pH culture on multi-biofuel production (hydrogen, ethanol, and 2,3-butanediol) by Enterobacter cloacae K1ga, isolated from koala and adapted to grow in 100 g dm⁻³ glucose. Batch cultures were performed in 1 dm³ bioreactors, controlling the pH at 5.5, 6.5, 7.5, and 9.2. Furthermore, cultures without pH control (with an initial pH of 9.2) were used as reference cultures. Controlling pH at 9.2 was detrimental to E. cloacae K1ga as no growth or biofuel production was observed. In contrast, reference cultures reached a maximum 2,3-butanediol (BDO) production (BDOP) of 22.9 ± 2.1 g dm⁻³ and ethanol production (EP) of 9.9 ± 0.7 g dm⁻³ and the highest hydrogen production (HP) of 2013.1 ± 275.7 cm³ dm⁻³. Meanwhile, a pH of 7.5 increased the accumulation of ethanol, obtaining the highest EP (14.0 ± 0.05 g dm⁻³). On the contrary, a pH of 5.5 was unfavourable for the fermentative metabolism of E. cloacae K1ga, showing the lowest production rates for the three biofuels and also the lowest EP (8.05 ± 0.35 g dm⁻³). The results demonstrate that the natural progression of pH during the growth of E. cloacae K1ga is an advantageous strategy for multi-biofuel production, since no tight pH control system is required. Full article

Selenium sulfide, the active ingredient of traditional antidandruff shampoos, is industrially produced from selenium dioxide (SeO₂) and hydrogen sulfide (H₂S) under acidic conditions. This reaction can also be carried out with natural H₂S and H₂S generated by sulfate-reducing bacteria (SRB). These bacteria are robust and, by relying on their conventional growth medium, also thrive in “waste” materials, such as a mixture of cabbage juice and compost on the one side, and a mixture of spoiled milk and mineral water on the other. In these mixtures, SRB are able to utilize the DL-lactate and sulfate (SO₄²⁻) present naturally and produce up to 4.1 mM concentrations of H₂S in the gas phase above a standard culture medium. This gas subsequently escapes the fermentation vessel and can be collected and reacted with SeO₂ in a separate compartment, where it yields, for instance, pure selenium sulfide, therefore avoiding the need for any cumbersome workup or purification procedures. Thus “harvesting” H₂S and similar (bio-)gases produced by the fermentation of organic waste materials by suitable microorganisms provides an elegant avenue to turn dirty waste into valuable clean chemical products of considerable industrial and pharmaceutical interest. Full article

The possibility of hydrogen (H₂) production from sizing waste, specifically starch-based substrates, was investigated through dark fermentation. Modified starch substrates produced less (up to 54% without heating and 18% after heating) H₂ than natural ones. However, heating modified starch samples led to 18% higher H₂ production than unheated ones, suggesting that high temperatures activate more favorable metabolic pathways. The highest H₂ production (215 mL/g_{TVS_substrate}) was observed with unheated natural starch, where the classic butyric–acetic fermentation pathway predominated. This variant also generated the highest CO₂ levels (250 mL/g_{TVS_substrate}), confirming the correlation between H₂ and CO₂ production in these pathways. Modified starch substrates shifted fermentation towards fatty acid chain elongation, reducing CO₂ production. The proportion of CO₂ in the fermentation gases correlated strongly with H₂ production across all variants. A decrease in total volatile solids (TVS) indicated effective organic matter conversion, while varying dissolved organic carbon (DOC) levels suggested different degradation rates. Nitrogen analysis (TN) revealed that the differences between variants were due to varying nitrogen processing mechanisms by microorganisms. These results highlight the potential of sizing waste as a substrate for bioH₂ production and offer insights for optimizing the process and developing industrial technologies for bioH₂ and other valuable products. Full article

In this study, 43 strains of Staphylococcus spp. and 22 strains of lactic acid bacteria (LAB), isolated from six representative fermented meat products (domestic and international), were subjected to a comprehensive safety evaluation, including hemolytic activity, catalase test, hydrogen sulfide production, and antibiotic susceptibility screening. Nine strains were selected for secondary screening based on safety criteria, fermentation characteristics, and acid and salt tolerance tests. Two optimal strains were identified—Staphylococcus saprophyticus LH-5 and Latilactobacillus sakei OFN-11—demonstrating excellent compatibility and no mutual antagonism. Both strains were non hemolytic, catalase positive, susceptible to some of the antibiotic tested, and did not produce hydrogen sulfide, mucus, or gas. These favorable fermentation characteristics included lipase/protease production, amino acid decarboxylase negativity, and salt and acid tolerance. Application experiments in fermented sausages were analyzed for 55 volatile compounds, related to meaty, fruity, and fatty aroma profiles compared to commercial starter cultures. The formulation including the selected strains exhibited lower acidity than its commercial unterparts while maintaining superior sensory and physicochemical attributes. These findings suggest that the S. saprophyticus LH-5 and L. sakei OFN-11 consortium holds promising potential as a starter culture for fermented meat products, offering technological advantages to become a fermentation agent that meets the preferences of Chinese consumers. Full article

Alfalfa (Medicago sativa L.) saponins (AS), primarily pentacyclic triterpenoids, may reduce methane emissions from goats (Capra hircus L.). This study evaluated the methane-suppressing potential of Aspergillus niger β-glucosidase-modified AS using in vitro rumen fermentation (0.10 mg/mL inoculum, 24 h incubation, gas chromatography detection). Among the 21 alfalfa cultivars, Pegasis (fall dormancy 9) exhibited the highest antioxidant efficacy (half maximum effective concentration 2.13 mg/mL) and the lowest ferric-reducing activity (0.32 μM Fe²⁺/g) (p < 0.05). Fresh/silage AS reduced methane proportions to 4.50–5.21% of total gas, while enzymatic biotransformation further decreased it to 3.34–3.48% (p < 0.05). Methanogen abundance declined by 20.10–44.93%, and general anaerobic fungi declined by 34.22–44.66% compared to untreated AS (p < 0.05). Metabolomics linked methane suppression to six pathways, including zeatin biosynthesis (via nucleotide metabolites accumulation) and prolactin signaling pathway (via bioactive molecules downregulation), suggesting impaired methanogen energy metabolism and hydrogen flux redirection as mechanisms. Enzymatic AS also enhanced volatile fatty acid production, indicating improved fiber digestion. These in vitro findings demonstrate that enzyme-treated AS modulates rumen fermentation through dual methane mitigation and nutrient utilization enhancement, offering a sustainable feed additive strategy for livestock. Full article

A copolymer of 3-hydroxybutyrate (3HB) and 3-hydoxyhexanoate (3HHx), PHBHHx, is a practical biodegradable plastic, and at present, the copolymer is produced at commercial scale via heterotrophic cultivation of an engineered strain of a facultative hydrogen-oxidizing bacterium, Cupriavidus necator, using vegetable oil as the carbon source. In our previous report, we investigated PHBHHx production from CO₂ via pH-stat jar cultivation of the newly created recombinants of C. necator under autotropic conditions, feeding the inorganic substrate gas mixture (H₂/O₂/CO₂ = 80:10:10 v/v%) into a recycled-gas closed-circuit (RGCC) culture system. The dry cell weight (DCW) and PHBHHx concentration with the best strain MF01/pBPP-ccr_MeJ_Ac-emd increased to 59.62 ± 3.18 g·L⁻¹ and 49.31 ± 3.14 g·L⁻¹, respectively, after 216 h. In this study, we investigated the high-concentration production of PHBHHx with a shorter cultivation time by using a jar fermenter equipped with a basket-shaped agitator to enhance oxygen transfer in the culture medium and by continuously supplying the gases with higher O₂ concentrations to maintain the gas composition within the reservoir at a constant ratio. The concentrations of ammonium and phosphate in the culture medium were maintained at low levels. As a result, the DCW and PHBHHx concentrations increased to 109.5 ± 0.30 g·L⁻¹ and 85.2 ± 0.62 g·L⁻¹ after 148 h, respectively. The 3HHx composition was 10.1 ± 0.693 mol%, which is suitable for practical applications. Full article

This study investigates the potential of sugar beet pulp (SBP), a lignocellulosic by-product of sugar production, as a low-cost substrate for biohydrogen and biomass generation using Escherichia coli under dark fermentation conditions. Two strains—BW25113 wild-type and a genetically engineered septuple mutant—were employed. SBP was pretreated via thermochemical hydrolysis, and the effects of substrate concentration, dilution, and glycerol supplementation were evaluated. Hydrogen production was highly dependent on substrate dilution and nutrient balance. The septuple mutant achieved the highest H₂ yield in 30 g L⁻¹ SBP hydrolysate (0.75% sulfuric acid) at 5× dilution with glycerol, reaching 12.06 mmol H₂ (g sugar)⁻¹ and 0.28 mmol H₂ (g waste)⁻¹, while the wild type under the same conditions yielded 3.78 mmol H₂ (g sugar)⁻¹ and 0.25 mmol H₂ (g waste)⁻¹. In contrast, undiluted hydrolysates favored biomass accumulation over H₂ production, with the highest biomass yield (0.3 g CDW L⁻¹) obtained using the septuple mutant in 30 g L⁻¹ SBP hydrolysate without glycerol. These findings highlight the potential of genetically optimized E. coli and optimized hydrolysate conditions to enhance the valorization of agro-industrial waste, supporting future advances in sustainable hydrogen bioeconomy and integrated waste biorefineries. Full article

The quality of persimmon wine is closely related to various compounds, including polysaccharides. Polysaccharides are an essential class of macromolecules that modulate the wine’s chemical and physical characteristics by influencing the colloidal state or interacting with other compounds through non-covalent bonds. Polyphenols, on the other hand, exhibit antioxidant properties and effectively neutralize free radicals. This study employed Luotian sweet persimmons and Brassica napus (rapeseed) as core ingredients for producing functional fermented wine. Using GC-MS, rapeseed polysaccharides were subjected to trifluoroacetic acid hydrolysis and then derivatized via silylation for qualitative analysis of their monosaccharide composition. Molecular docking and molecular dynamics simulations were performed to provide molecular-level insights into the interactions between D-glucopyranose from rapeseed polysaccharides and quercetin, a polyphenol present in persimmon wine. The objective was to explore the binding mechanisms of these compounds during fermentation and to assess how these molecular interactions in-fluence the wine’s flavor and stability. In addition, volatile flavor compounds in two types of persimmon wine (pure persimmon wine and oleoresin-enriched persimmon wine) were qualitatively and quantitatively analyzed using headspace solid-phase microextraction (SPME) combined with gas chromatography–mass spectrometry (GC-MS). The results reveal that D-glucopyranose forms hydrogen bonds with quercetin, modulating its redox behavior and thereby enhancing the antioxidant capacity of persimmon wine. The results from four in vitro antioxidant assays, including DPPH, ABTS, FRAP, and vitamin C analysis, demonstrate that the addition of rapeseed flowers improved the antioxidant activity of persimmon wine. HS-SPME-GC-MS analysis revealed that esters, alcohols, and aldehydes were the primary components contributing to the aroma of persimmon wine. Persimmon wines with varying levels of oleoresin addition exhibited significant differences in the contents of key compounds, which subsequently influenced the aroma complexity and flavor balance. In conclusion, these findings provide reliable data and a theoretical foundation for understanding the role of rapeseed flower in regulating the aroma profile of persimmon wine. These findings also offer theoretical support for a deeper understanding of the fermentation mechanisms of persimmon wine while providing practical guidance to optimize production processes, ultimately improving both product flavor and stability. This study fills a critical academic gap in understanding microscopic molecular interactions during fermentation and offers a novel perspective for innovation in the fermented food industry. Full article