Investigating the impact of lipid molecules and heat transfer on aroma compound formation and binding in roasted chicken skin: A UHPLC-HRMS and GC-O-MS study.

The UHPLCHRMS and Gas Chromatography-Olfactometry-Mass Spectrometry (GC-O-MS) techniques were applied to investigate effects of lipid molecules and heat transfer on the generation of aroma compounds in roasted chicken skin. Nineteen odorants were identified as most important aroma contributors based on odor activity values (OAVs) exceeding 1. Lipidomic analysis identified 3926 lipids in the samples, in which triglycerides (TG), phosphatidylcholine (PC), phosphatidylethanolamine (PE), and ceramide (Cer) had a contribution of 20.63%, 12.46%, 11.95%, and 11.39%, respectively. Furthermore, it was observed that PS(18:3e_22:5) and TG(18:0_18:1_18:1) serve as significant chemical markers for distinguishing chicken skin during the roasting (p < 0.05). TGs, notably TG(16:1_18:1_18:2) and TG(18:1_18:2_18:2), were postulated as key retainers for binding crucial aroma compounds. Meanwhile, PC, PE, and Cer played pivotal roles in aroma compound formation. Additionally, higher thermal conductivity and reduced thermal diffusivity significantly contributed to the formation of key odorants.

Characterization of key aroma compounds in roasted chicken using SPME, SAFE, GC-O, GC-MS, AEDA, OAV, recombination-omission tests, and sensory evaluation.

Aroma compounds in the roasted breasts, thighs and skins of chicken were isolated by solvent-assisted flavor evaporation (SAFE), quantitated by gas chromatography-olfactometry-mass (GC-O-MS), analyzed by aroma extract dilution analysis (AEDA), and determined by recombination-omission tests and sensory evaluation. Forty-seven aroma compounds in total, including aldehydes, ketones, furans, pyrazines, and furanones, were selected by AEDA. Twenty-five compounds were selected as pivotal odorants (Odor Activity Value, OAV ≥ 1). Twenty aroma compounds significantly were identified by recombination and omission experiments. Anethole (fennel odor) was the highest OAV (＞ 1843). Hexanal (grassy) and (E, E)-2,4-decadienal (meaty) were the most abundant aldehydes identified in roasted chicken. 1-octen-3-ol (mushroom), methanethiol (cabbage) and dimethyl trisulfide (areca, sulfur) were considered the key compounds of the breast and thighs of roasted chicken. Notably, furanone and pyrazines, 4-hydroxy-5-methyl-3(2H)-furanone (caramel, sweet and burning odor), 3-ethyl-2,5-dimethylpyrazine (nutty, toasty) and 2,3-dimethyl-5-ethylpyrazine (nutty, toasty) had the most significant effect on roasted chicken odor, especially in the skin.

Surfactants Used in Colloidal Synthesis Modulate Ni Nanoparticle Surface Evolution for Selective CO2 Hydrogenation.

Colloidal chemistry holds promise to prepare uniform and size-controllable pre-catalysts; however, it remains a challenge to unveil the atomic-level transition from pre-catalysts to active catalytic surfaces under the reaction conditions to enable the mechanistic design of catalysts. Here, we report an ambient-pressure X-ray photoelectron spectroscopy study, coupled with in situ environmental transmission electron microscopy, infrared spectroscopy, and theoretical calculations, to elucidate the surface catalytic sites of colloidal Ni nanoparticles for CO2 hydrogenation. We show that Ni nanoparticles with phosphine ligands exhibit a distinct surface evolution compared with amine-capped ones, owing to the diffusion of P under oxidative (air) or reductive (CO2 + H2) gaseous environments at elevated temperatures. The resulting NiPx surface leads to a substantially improved selectivity for CO production, in contrast to the metallic Ni, which favors CH4. The further elimination of surface metallic Ni sites by designing multi-step P incorporation achieves unit selectivity of CO in high-rate CO2 hydrogenation.

Characterization of key lipids for binding and generating aroma compounds in roasted mutton by UPLC-ESI-MS/MS and Orbitrap Exploris GC.

Lipids are the key aroma formation substrates and retainers relevant to the flavor quality. The lipids in the roasted mutton were investigated by UPLC-ESI-MS/MS and Orbitrap Exploris GC. The results showed that a total of 2488 lipids from 24 subclasses were identified in the roasted mutton, including 28.21% triglyceride (TG), 14.87% phosphatidylcholine (PC), and 11.03% phosphatidylethanolamine (PE). TG (16:0_18:1_18:1) and TG (18:0_18:0_18:1) might be the predominant lipids for binding aroma compounds. 488 Differential lipids from 20 subclasses were observed based on VIP > 1 and p < 0.05. The 61 out of 488 differential lipids, especially PC and PE, might predominantly contribute to the formation of aroma compounds. A total of 13 aroma compounds were determined as the characteristic odorants in the roasted mutton, including hexanal, heptanal, and 1-octen-3-ol. PC (30: 6) and PC (28: 3) were the potential markers for the discrimination of roasted mutton.

Microdroplet confined assembly enabling the scalable synthesis of titania supported ultrasmall low-valent copper catalysts for efficient photocatalytic activation of peroxymonosulfate.

The synthesis of highly dispersed low-valent copper catalysts is very challenging because they are prone to oxidation and sintering. Herein, scalable synthesis of ultrafine Cu(0)/Cu(i) catalysts supported on mesoporous titania microspheres is enabled by a one-step microdroplet confined assembly method. The extremely fast solute assembly in the microdroplet induces excellent metal precursor dispersion, reduces sol-gel crosslinking, and creates wrinkled microspheres with surface crusts and hollow cavities. This structural architecture allows the generation of an inner reductive gas environment during calcination in air to reduce Cu(ii) and create oxygen vacancy (OV) sites in titania. The obtained catalysts exhibit excellent performance in the photocatalytic activation of peroxymonosulfate (PMS) for pollutant degradation. The Cu(0) species with a surface plasmon resonance effect and OV-rich anatase facilitate efficient solar light utilization and charge separation. The intimate interface between Cu(i)/Cu(0) and anatase enables fast electron transfer and timely copper redox cycling to promote the activation of PMS.

An acid-base molecular assembly strategy toward N-doped Mo2C@C nanowires with mesoporous Mo2C cores and ultrathin carbon shells for efficient hydrogen evolution.

Molybdenum carbides are promising electrocatalysts for the hydrogen evolution reaction (HER). Rational design of morphology, composition and interfacial structure in Mo2C materials is essential to enhance their HER performance. Herein, an acid-base molecular assembly strategy is demonstrated for the synthesis of novel N-doped Mo2C@C core-shell nanowires (NWs) composed of mesoporous Mo2C cores with interconnected crystalline walls and ultrathin carbon shells. The strong interactions between the two precursors, adenine (Ade) and phosphomolybdic acid (PMA), lead to the formation of inter-molecular hybrid NWs during a hydrothermal process. The subsequent pyrolysis leads to confined growth of crystalline Mo2C NWs with inter-crystal mesopores (5 ~ 10 nm), formation of ultrathin carbon shells (~1.5 nm in thickness), and effective N doping. Such a structure architecture can provide abundant active sites, fast and diverse mass and electron transport paths, as well as stable reaction interfaces. The typical N-doped Mo2C@C NWs exhibit high HER performance with a low overpotential of 136 mV at 10 mA cm-2, a small Tafel slop of 58 mV dec-1, excellent durability and outstanding anti-poisoning performance against CO and H2S gases. Furthermore, the influences of several important factors, including the pyrolysis temperature, hydrothermal temperature and precursor mass ratio, on the morphology, composition and structural configuration of the resulted materials are elucidated and correlated with their HER performance. This work may provide a general strategy for the synthesis of other nanoscale metal carbides for various catalytic applications.

The Effect of Age on the Myosin Thermal Stability and Gel Quality of Beijing Duck Breast.

The effect of age (22, 30, 38, and 46 days) on Beijing duck breast myosin gels was investigated. The results showed that the water holding capacity (WHC) and gel strength were markedly improved at the age of 30 days. Differential scanning calorimetry suggested that the myosin thermal ability increased at the age of 30 and 38 days (p<0.05). A compact myosin gel network with thin cross-linked strands and small regular cavities formed at the age of 30 days, which was resulted from the higher content of hydrophobic interactions and disulfide bonds. Moreover, the surface hydrophobicity of myosin extracted from a 30-day-old duck breast decreased significantly under temperature higher than 80°C (p<0.05). This study illustrated that myosin extracted from a 30-day-old duck's breast enhanced and stabilized the WHC, thermal stability and molecular forces within the gel system. It concluded that age is an essential influencing factor on the myosin thermal stability and gel quality of Beijing duck due to the transformation of fibrils with different myosin character.

Slow and Sustained Release of Carbonate Ions from Amino Acids for Controlled Hydrothermal Growth of Alkaline-Earth Carbonate Single Crystals.

Alkaline-earth metal carbonate materials have attracted wide interest because of their high value in many applications. Various sources of carbonate ions (CO3 2-), such as CO2 gas, alkaline-metal carbonate salts, and urea, have been reported for the synthesis of metal carbonate crystals, yet a slow and sustained CO3 2- release approach for controlled crystal growth is much desired. In this paper, we demonstrate a new chemical approach toward slow and sustained CO3 2- release for hydrothermal growth of large alkaline-earth metal carbonate single crystals. Such an approach is enabled by the multiple hydrolysis of a small basic amino acid (arginine, Arg). Namely, the amino groups of Arg hydrolyze to form OH- ions, making the solution basic, and the hydrolysis of the guanidyl group of Arg is hydrothermally triggered to produce urea and ammonia, followed by the hydrolysis of urea to produce CO2 and ammonia and then the release of CO3 2- because of the reaction between CO2 and the OH- ions hydrolyzed from ammonia. Such a CO3 2- release behavior enables the slow and controlled growth of various carbonate single crystals over a wide range of pH values. The growth of uniform rhombohedron MgCO3 single crystals with variable morphologies and crystal sizes is studied in detail. The influences of reaction temperature, solution pH, precursor type, and concentration on the morphology and size of the resulting MgCO3 crystals are elucidated. The crystal evolution mechanism is also proposed and discussed with various supportive data.

Scalable Synthesis of Uniform Mesoporous Aluminosilicate Microspheres with Controllable Size and Morphology and High Hydrothermal Stability for Efficient Acid Catalysis.

Mesoporous aluminosilicates are promising solid acid catalysts. They are also excellent supports for transition metal catalysts for various catalytic applications. Synthesis of mesoporous aluminosilicates with controllable particle size, morphology, and structure, as well as adjustable acidity and high hydrothermal stability, is very desirable. In this work, we demonstrate the scalable synthesis of Al-SBA-15 microspheres with controllable physicochemical properties by using the microfluidic jet-spray-drying technology. The productivity is up to ∼30 g of dried particles per nozzle per hour. The Al-SBA-15 microspheres possess uniform controllable micron sizes (27.5-70.2 µm), variable surface morphologies, excellent hydrothermal stability (in pure steam at 800 °C), high surface areas (385-464 m2/g), ordered mesopore sizes (5.4-5.8 nm), and desirable acid properties. The dependence of various properties, including particle size, morphology, porosity, pore size, acidity, and hydrothermal stability, of the obtained Al-SBA-15 microspheres on experimental parameters including precursor composition (Si/Al ratio and solid content) and processing conditions (drying and calcination temperatures) is established. A unique morphology transition from smooth to wrinkled microsphere triggered by control of the Si/Al ratio and solid content is observed. The particle formation and morphology-evolution mechanism are discussed. The Al-SBA-15 microspheres exhibit high acid catalytic performance for aldol-condensation reaction between benzaldehyde and ethyl alcohol with a high benzaldehyde conversion (∼56.3%), a fast pseudo-first-order reaction rate (∼0.1344 h-1), and a high cyclic stability, superior to the commercial zeolite acid (H-ZSM-5). Several influencing factors on the catalytic performance of the obtained Al-SBA-15 microspheres are also studied.

A Molecular Foaming and Activation Strategy to Porous N-Doped Carbon Foams for Supercapacitors and CO2 Capture.

Hierarchically porous carbon materials are promising for energy storage, separation and catalysis. It is desirable but fairly challenging to simultaneously create ultrahigh surface areas, large pore volumes and high N contents in these materials. Herein, we demonstrate a facile acid-base enabled in situ molecular foaming and activation strategy for the synthesis of hierarchically macro-/meso-/microporous N-doped carbon foams (HPNCFs). The key design for the synthesis is the selection of histidine (His) and potassium bicarbonate (PBC) to allow the formation of 3D foam structures by in situ foaming, the PBC/His acid-base reaction to enable a molecular mixing and subsequent a uniform chemical activation, and the stable imidazole moiety in His to sustain high N contents after carbonization. The formation mechanism of the HPNCFs is studied in detail. The prepared HPNCFs possess 3D macroporous frameworks with thin well-graphitized carbon walls, ultrahigh surface areas (up to 3200 m2 g-1), large pore volumes (up to 2.0 cm3 g-1), high micropore volumes (up to 0.67 cm3 g-1), narrowly distributed micropores and mesopores and high N contents (up to 14.6 wt%) with pyrrolic N as the predominant N site. The HPNCFs are promising for supercapacitors with high specific capacitances (185-240 F g-1), good rate capability and excellent stability. They are also excellent for CO2 capture with a high adsorption capacity (~ 4.13 mmol g-1), a large isosteric heat of adsorption (26.5 kJ mol-1) and an excellent CO2/N2 selectivity (~ 24).

Amphiphilic Mesoporous Sandwich-Structured Catalysts for Selective Hydrogenation of 4-Nitrostyrene in Water.

Selective catalytic hydrogenation of substituted nitro compounds (NCs) of hydrophobic nature in aqueous solution using transition-metal-based catalysts is highly desirable yet fairly challenging. Herein, we propose the idea of amphiphilic mesoporous catalysts for selective hydrogenation of hydrophobic NCs in aqueous solution. The amphiphilic catalyst Co@Co-N-C@SBA-15 with a sandwich-like structure is constructed by a one-step solvent-free melting coating method. The catalyst has an external hydrophilic silica support that facilitates catalyst dispersion in water. It has unique Co-N-C catalytic layers uniformly coated in the inner mesopore surfaces of the silica support, which enhance the selective adsorption and activation of hydrophobic NCs. It has a high surface area (448.2 m2/g) and a uniform mesopore size (∼7.0 nm) for fast mass transportation. It possesses ultrafine metallic Co nanoparticles uniformly anchored within the N-doped carbon (N-C) layers for easy magnetic separation. These features make the catalyst excellent for the selective hydrogenation of 4-nitrostyrene to form 4-aminostyrene, with a high conversion of 98.0% in 1.0 h, a superior selectivity of 98.8%, and a good stability under mild conditions. A comprehensive study confirms the excellence of the amphiphilic mesoporous catalysts compared with other control catalysts. The Co-N sites are the intrinsic active sites. They can selectively adsorb and activate the nitro groups other than the vinyl groups, leading to superior selectivity. Water as the solvent results in the best performance compared with typical organic solvents probably because of an enhanced water-mediated hydrogen spillover and transfer.

Uniform mesoporous carbon hollow microspheres imparted with surface-enriched gold nanoparticles enable fast flow adsorption and catalytic reduction of nitrophenols.

Adsorption and catalytic conversion of nitrophenols (NPs) over carbon-based materials have attracted wide interest. Batch adsorption and catalytic reduction of NPs have been widely reported, but less attention has been paid to flow systems, which require high particle size uniformity and superior active site accessibility. Herein, uniform mesoporous carbon hollow microspheres with their surfaces enriched by Au nanoparticles (denoted as Au@UMCHMs) are synthesized. The surface-enriched Au nanoparticle loading is promoted by the unique feature, that is, relatively dense external layers and mesoporous inner shells, of the carbon microspheres and the simple impregnation-reduction method. The Au@UMCHMs possess uniform sizes of ∼82 µm, small shell thickness of ∼5.8 µm, high specific surface area (∼1587 m2/g), and uniform mesopores (2.1 and 5.8 nm). They show excellent performance for flow adsorption and catalytic reduction of 4-nitrophenol (4-NP), superior to that of conventional Au-loaded carbon materials. In flow adsorption of 4-NP, the Au@UMCHMs show a fast and complete removal efficiency with high adsorption capacities (∼223 mg/g at breakthrough). They show outstanding performance in flow catalytic reduction of 4-NP. 4-NP with high concentrations (up to 100 mg/L) can be ultrafast and completely catalytically reduced to 4-aminophenol (4-AP) under rapid flow rates (up to ∼25 mL/min).

Solid-state nanocasting synthesis of ordered mesoporous CoNx-carbon catalysts for highly efficient hydrogenation of nitro compounds.

Selective catalytic hydrogenation of nitro compounds (NCs) is an attractive challenge with significant research being focused on the development of cobalt (Co)-based nanocatalysts. Herein, in order to achieve high activity and selectivity for the catalytic hydrogenation of NCs and identify the essential active Co-containing sites, a facile solid-state nanocasting approach is developed for the controllable synthesis of CoNx-doped ordered mesoporous carbon materials (denoted as CoNx-OMCs). Compared with the previous nanocasting synthesis of mesoporous catalysts, the current method requires no solvent and relies on melting and interfacial chemical interactions between silica and the precursors for loading and casting, and chemical coordination among the precursors for the formation and dispersion of the active sites. The resulting CoNx-OMCs possess high surface areas (∼941 m2 g-1), ordered mesopores (∼4.0 nm), high N content (∼6.8 wt%) and abundant CoNx sites and fine metallic Co nanoparticles. With molecular H2 as the reducing agent, the optimized catalyst delivers very attractive catalytic activities (100% conversions), selectivities (close to 100% selectivities) and stability (no obvious performance decay after cycling) in the hydrogenation of a series of NCs carrying diverse groups in aqueous solutions under mild conditions. A comparative study clearly reveals that the CoNx sites, not the metallic Co nanoparticles, are the key active sites for the hydrogenation of NCs. The CoNx sites are found to preferentially adsorb nitro groups, thus activating them and promoting their reduction. A detailed study reveals that the high catalytic performance relies on the synergistic cooperation of the catalyst composition and structure, which are tuneable by adjusting the synthetic conditions.

Conformal Coating of Co/N-Doped Carbon Layers into Mesoporous Silica for Highly Efficient Catalytic Dehydrogenation-Hydrogenation Tandem Reactions.

To maximize the utilizing efficiency of cobalt (Co) and optimize its catalytic activity and stability, engineering of size and interfacial chemical properties, as well as controllable support are of ultimate importance. Here, the concept of coating uniform thin Co/N-doped carbon layers into the mesopore surfaces of mesoporous silica is proposed for heterogeneous aqueous catalysis. To approach the target, a one-step solvent-free melting-assisted coating process, i.e., heating a mixture of a cobalt salt, an amino acid (AA), and a mesoporous silica, is developed for the synthesis of mesoporous composites with thin Co/N-doped carbon layers uniformly coated within mesoporous silica, high surface areas (250-630 m2 g-1 ), ordered mesopores (7.0-8.4 nm), and high water dispersibility. The strong silica/AA adhesive interactions and AA cohesive interactions direct the uniform coating process. The metal/N coordinating, carbon anchoring, and mesopore confining lead to the formation of tiny Co nanoclusters. The carbon intercalation and N coordination optimize the interfacial properties of Co for catalysis. The optimized catalyst exhibits excellent catalytic performance for tandem hydrogenation of nitrobenzene and dehydrogenation of NaBH4 with well-matched reaction kinetics, 100% conversion and selectivity, high turnover frequencies, up to ≈6.06 molnitrobenzene molCo-1 min-1 , the highest over transition-metal catalysts, and excellent stability and magnetic separability.

Spray-drying-assisted reassembly of uniform and large micro-sized MIL-101 microparticles with controllable morphologies for benzene adsorption.

Significant research has been focused on the synthesis of metal-organic frameworks (MOFs) with controllable compositions and structures, while much fewer works have been devoted to the construction of large micro-sized MOFs with uniform sizes and morphologies, which could be beneficial for practical applications. In this paper, a unique microfluidic jet spray drying technology has been adopted to reassemble nano-sized MIL-101 building blocks into hierarchical microparticles with uniform and large particle sizes. Specifically, suspension precursors of nano-sized MIL-101 building blocks are atomized into uniform droplets and then converted to microparticles on a one-to-one basis through a fast and scalable spray drying process. The particle size and morphology can be controlled by adjusting the solid concentration of the suspension and the drying temperature. The particle formation process with evolution of different morphologies are discussed. The resultant uniform MIL-101 microparticles possess hierarchical porosities and maintain the intrinsic crystal structure, microporosity and thermal stability of the nano-sized building blocks. They demonstrate a high efficiency toward benzene adsorption from n-octane solutions with high adsorption rates and very high adsorption capacities under batch conditions. Moreover, the large particle size and hierarchical structure make them applicable as filler of a fixed bed for dynamic flow separation of benzene from n-octane solutions with promising performance. The microfluidic jet spray drying technology can also be extended for the reassembly of other uniform MOF microparticles.