The mechanisms of pH regulation on promoting volatile fatty acids production from kitchen waste.

The anaerobic acid production experiments were conducted with the pretreated kitchen waste under pH adjustment. The results showed that pH 8 was considered to be the most suitable condition for acid production, especially for the formation of acetic acid and propionic acid. The average value of total volatile fatty acid at pH 8 was 8814 mg COD/L, 1.5 times of that under blank condition. The average yield of acetic acid and propionic acid was 3302 mg COD/L and 2891 mg COD/L, respectively. The activities of key functional enzymes such as phosphotransacetylase, acetokinase, oxaloacetate transcarboxylase and succinyl-coA transferase were all enhanced. To further explore the regulatory mechanisms within the system, the distribution of microorganisms at different levels in the fermentation system was obtained by microbial sequencing, results indicating that the relative abundances of Clostridiales, Bacteroidales, Chloroflexi, Clostridium, Bacteroidetes and Propionibacteriales, which were great contributors for the hydrolysis and acidification, increased rapidly at pH 8 compared with the blank group. Besides, the proportion of genes encoding key enzymes was generally increased, which further verified the mechanism of hydrolytic acidification and acetic acid production of organic matter under pH regulation.

Emission characteristics of biogenic volatile organic compounds in a subtropical pristine forest of southern China.

Emission characteristics of biogenic volatile organic compounds (BVOCs) from dominant tree species in the subtropical pristine forests of China are extremely limited. Here we conducted in situ field measurements of BVOCs emissions from representative mature evergreen trees by using dynamic branch enclosures at four altitude gradients (600-1690 m a.s.l.) in the Nanling Mountains of southern China. Composition characteristics as well as seasonal and altitudinal variations were analyzed. Standardized emission rates and canopy-scale emission factors were then calculated. Results showed that BVOCs emission intensities in the wet season were generally higher than those in the dry season. Monoterpenes were the dominant BVOCs emitted from most broad-leaved trees, accounting for over 70% of the total. Schima superba, Yushania basihirsuta and Altingia chinensis had relatively high emission intensities and secondary pollutant formation potentials. The localized emission factors of isoprene were comparable to the defaults in the Model of Emissions of Gases and Aerosols from Nature (MEGAN), while emission factors of monoterpenes and sesquiterpenes were 2 to 58 times of those in the model. Our results can be used to update the current BVOCs emission inventory in MEGAN, thereby reducing the uncertainties of BVOCs emission estimations in forested regions of southern China.

Emission characteristics and probabilistic health risk of volatile organic compounds from leather sofa.

Furniture is identified as a vital volatile organic compound (VOC) emission source in the indoor environment. Leather has become the most common raw and auxiliary fabric material for upholstered furniture, particularly with extensive consumption in sofas, due to its abundant resources and efficient functions. Despite being widely traded across the world, little research has been conducted on the VOCs released by leather materials and their health risk assessment in the indoor environment. Accordingly, this study investigated the VOC emissions of leather with different grades and the health risk of the inhalation exposure. Based on the ultra-fast gas phase electronic nose (EN) and GC-FID/Qtof, the substantial emissions of aliphatic aldehyde ketones (Aks), particularly hexanal, appear to be the cause of off-flavor in medium and low grade (MG and LG) sofa leathers. The health risk assessment indicated that leather materials barely pose non-carcinogenic and carcinogenic effects to residents. Given the abundance of VOC sources and the accumulation of health risks in the indoor environment, more stringent specifications concerning qualitative and quantitative content should be extended to provide VOC treatment basic for the manufacturing industry and obtain better indoor air quality.

Chemical characteristics and sources apportionment of volatile organic compounds in the primary urban area of Shijiazhuang, North China Plain.

VOCs (Volatile organic compounds) exert a vital role in ozone and secondary organic aerosol production, necessitating investigations into their concentration, chemical characteristics, and source apportionment for the effective implementation of measures aimed at preventing and controlling atmospheric pollution. From July to October 2020, online monitoring was conducted in the main urban area of Shijiazhuang to collect data on VOCs and analyze their concentrations and reactivity. Additionally, the PMF (positive matrix factorization) method was utilized to identify the VOCs sources. Results indicated that the TVOCs (total VOCs) concentration was (96.7 ± 63.4 µg/m3), with alkanes exhibiting the highest concentration of (36.1 ± 26.4 µg/m3), followed by OVOCs (16.4 ± 14.4 µg/m3). The key active components were alkenes and aromatics, among which xylene, propylene, toluene, propionaldehyde, acetaldehyde, ethylene, and styrene played crucial roles as reactive species. The sources derived from PMF analysis encompassed vehicle emissions, solvent and coating sources, combustion sources, industrial emissions sources, as well as plant sources, the contribution of which were 37.80%, 27.93%, 16.57%, 15.24%, and 2.46%, respectively. Hence, reducing vehicular exhaust emissions and encouraging neighboring industries to adopt low-volatile organic solvents and coatings should be prioritized to mitigate VOCs levels.

Effect of temperature regulation on microbial community, volatile flavours, amino acid profiles, and iridoid glycosides during noni (Morinda citrifolia L.) fruit fermentation.

Noni fruit has an unpleasant flavour but is highly bioactive. Therefore, it is necessary to clarify the effect of temperature regulation on quality of fermented noni fruit. In the present study, the formation of flavours, amino acid profiles, and iridoid glycosides during noni fruit fermentation at different temperatures were investigated. We initially found that different temperatures affected core microbial communities. The general evolutionary trends of Acetobacter and Gluconobacter were influenced by different temperatures. Furthermore, high temperature helped maintain low octanoic and hexanoic acids. Subsequently, we found that high temperature improved total amino acids and iridoid glycosides. The correlation network analysis revealed that bacterial communities impacted the quality (volatile flavours, amino acid profiles, and iridoid glycosides) of fermented noni fruit. Overall, altering the temperature induced variations in microbial communities and quality during the noni fruit fermentation process. These results are instrumental in the pursuit of quality control in natural fermentation processes.

Chemical profiling and probiotic viability assessment in Gueuze-style beer: Fermentation dynamics, metabolite and sensory characterization, and in vitro digestion resistance.

Probiotic viability, metabolite concentrations, physicochemical parameters, and volatile compounds were characterized in Gueuze beers formulated with probiotic lactic acid bacteria (LAB) and yeast. Additionally, the sensory profile of the beers and the resistance of the probiotics to digestion were determined. The use of 2 International Bitterness Units resulted in high concentrations of probiotic LAB but a decline in probiotic yeast as pH decreased. Secondary fermentation led to the consumption of maltose, citric acid, and malic acid, and the production of lactic and propionic acids. Carbonation and storage at 4 °C had minimal impact on probiotic viability. The addition of probiotic LAB resulted in a distinct aroma profile with improved sensory characteristics. Our results demonstrate that sour beers produced with probiotic LAB and a probiotic yeast, and fermented using a two-step fermentation process, exhibited optimal physicochemical parameters, discriminant volatile compound profiles, promising sensory characteristics, and high probiotic concentrations after digestion.

Enhanced VOC emission with increased temperature contributes to the shift of O3-precursors relationship and optimal control strategy.

Assessing the impact of anthropogenic volatile organic compounds (VOCs) on ozone (O3) formation is vital for the management of emission reduction and pollution control. Continuous measurement of O3 and the major precursors was conducted in a typical light industrial city in the YRD region from 1 May to 25 July in 2021. Alkanes were the most abundant VOC group, contributing to 55.0% of TVOCs concentration (56.43 ± 21.10 ppb). OVOCs, aromatics, halides, alkenes, and alkynes contributed 18.7%, 9.6%, 9.3%, 5.2% and 1.9%, respectively. The observational site shifted from a typical VOC control regime to a mixed regime from May to July, which can be explained by the significant increase of ROx production, resulting in the transition of environment from NOx saturation to radical saturation with respect to O3 production. The optimal O3 control strategy should be dynamically changed depending on the transition of control regime. Under NOx saturation condition, minimizing the proportion of NOx in reduction could lead to better achievement of O3 alleviation. Under mixed control regime, the cut percentage gets the top priority for the effectiveness of O3 control. Five VOCs sources were identified: temperature dependent source (28.1%), vehicular exhausts (19.9%), petrochemical industries (7.2%), solvent & gasoline usage (32.3%) and manufacturing industries (12.6%). The increase of temperature and radiation would enhance the evaporation related VOC emissions, resulting in the increase of VOC concentration and the change of ROx circulation. Our results highlight determination of the optimal control strategies for O3 pollution in a typical YRD industrial city.

Assessing the potential of olive mill solid waste as feedstock for methane and volatile fatty acids production via anaerobic bioprocesses.

The extensive production of olive mill solid waste (OMSW) from olive oil industry in the Mediterranean basin claims effective treatments and valorization strategies. This study aims to elucidate the potential of anaerobic digestion (AD) and anaerobic fermentation (AF) to convert pre-treated OMSW into biogas (CH4) and volatile fatty acids (VFA), respectively. The two thermal treatment conditions (65 °C and 180 °C) that are being implemented in the industry that manages the OMSW were tested. Comparing the two treatments aims to demonstrate the influence on the AD process of the degree of solubilization and degradation of the metabolites produced from the same substrate. AD of OMSW treated at low-temperature (65 °C) exhibited similar methane yields (195 ± 8mL CH4/g volatile solid (VS)) to raw OMSW. AD of the solid phase (SP) after high-temperature treatment with acid addition at 180°C resulted in methane yields comparable to raw OMSW while the liquid phase (LP) exhibited low methane yields (85 ± 10mL CH4/g VS). Nevertheless, LP/180 °C exhibited the highest VFA bioconversion at 27.6%, compared to less than 10% for SP/180ºC, SP/65 °C, and raw OMSW. The VFA profile showed notable variations with thermal treatment temperatures. Propionic acid dominated at SP/65 °C, while acetic acid became the primary VFA at 180 °C. Furthermore, significant degradation rates of phenolic compounds and furans were observed during the final day of both anaerobic processes. Overall, these findings suggest that AD is more suitable for raw OMSW, treated at low temperature and SP at high temperature, while AF offers a promising alternative for high-temperature-treated LP.

Applications of Pythium- and Phytophthora-produced volatiles in plant disease control.

Volatile organic compounds (VOCs) mediate biological interactions and are produced by Pythium and Phytophthora species. These VOCs are biotechnologically relevant because the genera include important plant pathogens, whereby VOCs can aid in disease detection, and biological control agents, whereby VOCs contribute to disease control. Studies on VOC production, identification, and characterization of individual VOCs produced by Pythium and Phytophthora species are reviewed. VOCs detected in plants infected with Phytophthora species are also reviewed as potentially oomycete-derived VOCs. The Pythium- and Phytophthora-produced VOCs are compared with other microorganisms, and the main effects of these VOCs on microbial inhibition and plant-mediated effects are reviewed. These effects are summarized from direct demonstration studies and inferences based on the known functions of the identified Pythium- and Phytophthora-produced VOCs. There are two main applications of VOCs to plant disease control: the use of VOCs to detect pathogenic Pythium and Phytophthora species, e.g., e-nose detecting systems, and the use of VOC-producing biological control agents, e.g., Pythium oligandrum. Future research could understand how the VOCs are produced to engineer VOC levels in strains, analyze more oomycete species and strains, accurately quantify the VOCs produced, and exploit recent developments in analytical chemistry technology. KEY POINTS: • Compiled inventory of volatiles produced by Phytophthora and Pythium species • Volatilomes contain microbe-inhibiting and plant growth-promoting compounds • Volatile potential in disease detection and control supports analyzing more species.

Yeast culture enhances long-term fermentation of corn straw by ruminal microbes for volatile fatty acid production: Performance and mechanism.

Ruminal microbes can efficiently ferment biomass waste to produce volatile fatty acids (VFAs). However, keeping long-term efficient VFA production efficiency has become a bottleneck. In this study, yeast culture (YC) was used to enhance the VFA production in long-term fermentation. Results showed that YC group improved the volatile solid removal and VFA concentration to 47.8% and 7.82 g/L, respectively, 18.6% and 16.1% higher than the control, mainly enhancing the acetic, propionic, and butyric acid production. YC addition reduced the bacterial diversity, changed the bacterial composition, and improved interactions among bacteria. The regulation mechanism of YC was to increase the abundance and activity of hydrolytic and acidogenic bacteria such as Prevotella and Treponema, improve bacterial interactions, and further promote expression of functional genes. Ultimately, a long-term efficient ruminal fermentation of corn straw into VFAs was achieved.