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Consumers are becoming increasingly aware of the health benefits of dairy ingredients. However, products fortified with dairy proteins are experiencing considerable aroma challenges. Practices to improve the flavor quality of dairy proteins require a comprehensive understanding of the nature and origins of off-aroma. Unfortunately, existing information from the literature is fragmentary. This review presents sensory lexicons and chemical structures of off-aromas from major dairy ingredients, and it explores their possible precursors and formation mechanisms. It was found that similar chemical structures often contributed to similar off-aroma descriptors. Lipid degradation and Maillard reaction are two primary pathways that commonly cause aroma dissatisfaction. Traditional and novel flavor chemistry tools are usually adopted for off-aroma measurements in dairy ingredients. Strategies for improving aroma quality in dairy derived products include carefully selecting starting materials for formulations, and actively monitoring and optimizing processing and storage conditions.

Ethyl carbamate (EC) is a genotoxic and carcinogenic compound that is also a by-product of fermented foods (bread, sour milk, soy cheese, etc.) and alcoholic beverages (wine, sake, distilled liquor, etc.). Studies have showed that ethyl carbamate is ingested by humans primarily through the consumption of alcoholic beverages. Many countries have thus established EC limits for alcoholic beverages. Chinese liquor (Baijiu) is a traditional and unique distilled liquor, which has a huge consumption in China due to its excellent color, flavor, and taste. Therefore, the control of EC in Chinese liquor is of great significance. This review summarized for the first time the progress in presence level, analysis method, formation mechanism, and elimination strategy of EC of Chinese liquor in recent decades.Key points• GC-MS and HPLC are the main methods to quantify EC in Chinese liquor.• EC is formed in the fermentation, distillation, and storage stage.• EC content can be reduced from raw material, microorganism, and production process.

5-hydroxymethyl-2-furaldehyde (5-HMF) is an important substance that affect quality of honey and shows toxicity for humans and honey bees. The pathway of 5-HMF formation in honey is still unknown. In this study, we tested the effect of thermal treatment (at 90 °C for 4 h) on the formulation of 5-HMF formulation in rapeseed with varied honey composition. 5-HMF content of honey increased at higher water content, Ca2+ and Mg2+ content and lower pH. However, the formation of 5-HMF was not significantly influenced by glucose, fructose, Na+, or K+ contents. Furthermore, different content of proline, the most abundant amino acid in honey (a substance in Maillard reaction), had no effect on 5-HMF formation. Free acids in honey can catalyze fructose and glucose to form 5-HMF. These results suggest that dehydration of glucose or fructose, instead of the Maillard reaction, is the main pathway of 5-HMF formation in honey. This study gives new insights for the mechanisms of 5-HMF formation and provides method for reducing 5-HMF formation during honey processing.

The formation pathway of aqueous-phase colloidal semiconductor magic-size clusters (MSCs) remains unrevealed. In the present work, we demonstrate, for the first time, a precursor compound (PC)-enabled formation pathway of aqueous-phase CdSe MSCs exhibiting a sharp absorption peaking at about 420 nm (MSC-420). The CdSe MSC-420 is synthesized with CdCl 2 and selenourea as the respective Cd and Se sources, and with 3-mercaptopropionic acid or L-cysteine as a ligand. Absorption featureless CdSe PCs form first in the aqueous reaction batches, which transform to MSC-420 in the presence of primary amines. The coordination between primary amine and Cd 2+ on PCs may be responsible to the PC-to-MSC transformation. Upon increasing the reactant concentrations or decreasing the CdCl 2 -ligand feed molar ratios, the Cd precursor self-assembles into large aggregates, which may encapsulate the resulting CdSe PCs and inhibit their transformation to MSC-420. The present study sheds essential light on the syntheses and formation mechanisms of nanocrystals.

In order to investigate the formation pathway of hydrochar during hydrothermal carbonization (HTC) and to identify the optimal process conditions for producing high-quality pyrolysis feedstock, the effect of hydrothermal temperature (220, 250, and 280 °C) on tar and hydrochar properties were analyzed by GC-MS, XRD, XPS, FT-IR, and SEM using protein-rich brewer’s spent grain (BSG) as raw material. The results showed that aromatic compounds play a major role in tar production. Increasing hydrothermal temperature significantly enhanced volatile matter removal and consequently increased the fixed carbon content from 23.14 wt.% in HC-220 to 27.07 wt.% in HC-280, while the catalytic effect of H3O+ produced by high-temperature water facilitated the dehydration and decarboxylation reactions, resulting in a reduction in the H/C atomic ratio from 1.44 in HC-220 to 1.25 in HC-280 and the O/C atom ratio from 0.32 in HC-220 to 0.25 in HC-280. HC-280 exhibited superior fuel properties, with a high heating value (HHV) of 35.4 MJ/kg. XPS analysis indicated that elevated temperatures promote the conversion of sp3 C to sp2 C (the value of sp2 C/sp3 C increased from 1.13 in HC-220 to 1.49 in HC-280), significantly increasing the aromatic condensation degree of hydrochar. The more pronounced reduction in the -OH content compared to -COOH indicated that dehydration reactions predominated over decarboxylation. Finally, the formation pathways of hydrochar during HTC were revealed based on the properties of different products. The results demonstrate that HTC is an effective method for converting BSG into pyrolysis feedstock with potential applications in energy production. Future work should focus on the technical–economic assessment of the process at a pilot scale and evaluating the hydrochar’s performance in real pyrolysis systems.

Few studies focused on the emission of polychlorinated- ρ -dibenzodioxins and dibenzofurans (PCDD/F) from different kinds of waste incinerators. This study was conducted in a full-scale MSW incineration plant to investigate the influence of different incinerator types on PCDD/F. Experimental results indicated that the 2,3,7,8-PCDD/F concentration in the inlet gas of the air pollution control system (APCS) in the studied fluidized bed was higher (2.03 ng I-TEQ/Nm 3 ) than that of the grate (0.77 ng I-TEQ/Nm 3 ). But gas in the outlet of APCS from both incinerators had an approximate concentration, lower than the Chinese emission limit of 0.1 ng I-TEQ/Nm 3 . Similar distribution patterns were observed for 2,3,7,8-PCDD/Fs, as well as 136 PCDD/F congeners. Specifically, OCDD and 1,2,3,4,6,7,8-HpCDD were major isomer constituents for 2,3,7,8-PCDD/F isomers. In terms of formation pathways, a similar formation mechanism was observed based on fingerprint characteristics of 136 PCDD/F congeners. De novo synthesis was the dominating formation pathway for both incinerators. Meanwhile, DD/DF chlorination was another contributor to PCDD/F formation, which in the fluidized bed was higher. In addition, little correlation (0.009 < R 2 < 0.533) between conventional pollutants (HCl, CO, PM) and PCDD/Fs was found, suggesting little high-temperature synthesis observed and verifying the dominance of de novo synthesis. Graphical abstract

The challenge in achieving large-scale biogas production still lies in the biogas fermentation process at low temperatures. Our goal was to delve into the metabolic pathway behind the formation of biogas at these lower temperatures, focusing on the dominant bacterial and archaeal communities. Employing a batch system with activated sludge inoculum at 10°C, we fermented cow manure at 12°C for 150 days. Through genetic sequencing and taxonomic analysis using OTUs from the 16S rDNA gene, we investigated bacterial and archaeal species. Correlation analysis between their abundance was conducted using Pearson correlation and t-tests via IBM SPSS Statistics. Our findings revealed a biogas production of around 0.74 L/day, with CH4 levels surpassing 0.45 L/g VS. Peak efficiency occurred between day 60 and 110, reaching its apex on day 90. Clostridium cellulovorans dominated, ranging from 13.9% to 27%, followed by Terrisporobacter petrolarius, around 16.2% to 23%. Specifically, the formation of biogas (CH4) predominantly occurred through the H2 pathway, led by significant hydrogenotrophic Archaea OTUs like Methanocorpusculum sinense (ranging from 4.95% to 37.10%) and Methanobrevibacter millerae (with relative abundances between 2.00% and 11.20%)

The South China Sea (SCS) is a crucial region for studying atmospheric aerosols, given its unique geographical location and the interaction of various natural and anthropogenic sources. In this study, we measured the isotopic characteristics of sulfate and nitrate in PM2.5 and utilized a Bayesian isotope mixing model (SIAR) to analyze their sources and formation pathways. Sulfur isotopic values in sulfate (δ34S-SO42−) were 8.7 ± 1.8‰, while nitrogen and oxygen isotopic values in nitrate (δ15N-NO3− and δ18O-NO3−) were −0.9 ± 2.4‰ and 52.3 ± 7.3‰, respectively. The results revealed that sulfate was primarily influenced by marine biogenic sulfur emissions (mostly dimethyl sulfide, DMS), fossil fuel combustion, and biomass burning. Nitrate formation was dominated by the NO2 + •OH pathway (accounting for 69.8–85.7%), with significant contributions from vehicle emissions, biomass burning, and lightning. These findings offer key insights into the complex interactions between natural and anthropogenic aerosol sources in the SCS, contributing to a broader understanding of marine aerosol chemistry.

Halonitromethanes (HNMs), a representative nitrogen-containing disinfection byproduct, have gained significant concerns due to their higher cytotoxicity and genotoxicity. UV/chlorination is considered a promising alternative disinfection technology for chlorination. This study aimed to investigate the HNMs formation from benzylamine (BZA) during UV/chlorination. The experimental results revealed that the yields of HNMs initially raised to a peak then dropped over time. Higher chlorine dosage and BZA concentration promoted the formation of HNMs, whereas alkaline pH inhibited their formation. The presence of bromine ion (Br − ) not only converted chlorinated-HNMs (Cl-HNMs) to brominated (chlorinated)-HNMs Br (Cl)-HNMs) and brominated-HNMs (Br-HNMs) but also enhanced the total concentration of HNMs. Besides, the calculated cytotoxicity index (CTI) and genotoxicity index (GTI) of HNMs were elevated by 68.97% and 60.66% as Br − concentration raised from 2 to 6 µM. The possible formation pathways of HNMs from BZA were proposed based on the intermediates identified by a gas chromatography/mass spectrometry (GC/MS). In addition, the formation rules of HNMs in actual water verified the results in deionized water during UV/chlorination. The results of this study provide basic data and a theoretical basis for the formation and control of HNMs, which is conducive to applying UV/chlorination.

Co-combustion of sewage sludge (SS) and coal was developed rapidly in China, however, less attention was paid to the formation characteristics of polychlorinated dibenzo- p -dioxins and dibenzofurans (PCDD/Fs) and the influence factors, such as the catalytic metals (CuCl 2 , FeCl 3 , ZnCl 2 , CuO, Fe 2 O 3 , and ZnO), sources of carbon and chlorine. During the co-combustion of SS (2.5 wt.%) and coal (97.5 wt.%), the formation content of PCDD/Fs was 0.51 ng g –1 and 0.01 ng I-TEQ g –1 . By adding metal chlorides (2.0 wt.% CuCl 2 , FeCl 3 , and ZnCl 2 ), the formation contents of PCDD/Fs were increased significantly to 148.99, 67.38, and 53.63 ng g –1 (i.e., 2.10, 1.09, and 1.34 ng I-TEQ g –1 ), respectively, while the metal oxides (2.0 wt.% CuO, Fe 2 O 3 , and ZnO) only increased the PCDD/F contents to 1.27, 0.76, and 0.57 ng g –1 (0.03, 0.01, and 0.02 ng I-TEQ g –1 ), respectively. That is, the promotion effect of different metal additives on PCDD/F formation followed a sequence of CuCl 2 (292×) > FeCl 3 (132×) > ZnCl 2 (105×) ≫ CuO (2.5×) > Fe 2 O 3 (1.5×) > ZnO (1.1×), wherein the metal chlorides showed 2 orders of magnitude higher promotion than that of metal oxides. The proportion of highly chlorinated PCDD/Fs was further increased after adding metal chlorides, while the additional metal oxides decreased it. The de novo synthesis was revealed as the major formation pathway of PCDD/Fs except for adding ZnO. The CuCl 2 and FeCl 3 can also enhance the chlorination routes to generate PCDD/Fs. Only ZnO showed the promotion effect on the CP-route. The chlorine source was an essential limiting factor for generating PCDD/Fs, and the chlorine from metal chlorides was the preference source compared with that contained in SS and coal. The results have important reference value for controlling PCDD/Fs formation in the co-combustion process of SS and coal.