Comprehensive Two-dimensional Gas Research Articles

Comparative lipidome and transcriptome provide novel insights into zero-valent iron nanoparticle-treated Fremyella diplosiphon.

Understanding the intricate interplay between nanoparticle-mediated cyanobacterial interactions is pivotal in elucidating their impact on the transcriptome and lipidome. In the present study, total fatty acid methyl esters (FAMEs) in the wild-type (B481-WT) and transformant (B481-SD) Fremyella diplosiphon strains treated with nanoscale zero-valent iron nanoparticles (nZVIs) were characterized, and transcriptome changes analyzed. Comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry revealed a 20-25% higher percentage of FAMEs in nZVI-treated F. diplosiphon strain B481-SD compared to B481-WT. Accumulation of alkanes was significantly higher (> 1.4 times) in both strains treated with 25.6 mg L-1 nZVIs compared to the untreated control. In addition, we observed significantly higher levels of monounsaturated FAMEs (11%) in B481-WT in 3.2 (11.34%) and 25.6 mg L-1 (11.22%) nZVI-treated cells when compared to the untreated control (7%). Analysis of the F. diplosiphon transcriptome treated with 3.2mg L-1 revealed a total of 1811 and 1651 genes that were differentially expressed in B481-SD and B481-WT respectively. While the expression of iron uptake and ion channel genes was downregulated, genes coding for photosynthesis, pigment, and antioxidant enzymes were significantly (p < 0.05) upregulated in B481-SD treated with 3.2 mg L-1 nZVIs compared to the untreated control. This study on essential FAMEs and regulation of genes in nZVI-treated F. diplosiphon strains provides a molecular framework for optimization of metabolic pathways in this model species.

Unrevealing the Halyomorpha halys Damage Fingerprint on Hazelnut Metabolome by Multiomic Platforms and AI-Aided Strategies.

The brown marmorated stink bug (Halyomorpha halys) poses a significant threat to hazelnut crops by affecting kernel development and causing quality defects, reducing the market value. While previous studies have identified bitter-tasting compounds in affected kernels, the impact of stink bug feeding on the hazelnut metabolome, particularly concerning aroma precursors, remains underexplored. This study aims to map the nonvolatile metabolome and volatilome of hazelnut samples obtained by caging H. halys on different cultivars in two locations to identify markers for diagnosing stink bug damage. Using a multiomic approach involving headspace solid-phase microextraction (HS-SPME), comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOF MS), and liquid chromatography-high-resolution mass spectrometry (LC-HRMS), both raw and roasted hazelnuts are analyzed, with artificial intelligence (AI) and machine learning tools employed to explore data correlations. The study finds that the hazelnut metabolome and volatilome exhibit high chemical complexity with significant classes of compounds such as aldehydes, ketones, alcohols, and terpenes identified in both raw and roasted hazelnuts. Multivariate analysis indicates that the orchard location significantly impacts the metabolome, followed by damage type, with cultivar differences being less pronounced. Partial least-squares discriminant analysis (PLS-DA) models achieve high predictive accuracy for orchard location (99%) and damage type (≈80%), with the roasted volatilome showing the highest predictive accuracy. Correlation matrices reveal significant relationships between raw hazelnut metabolites and aroma compounds in roasted samples, suggesting potential markers for stink bug damage that could guide the quality assessment and mitigation strategies. Data fusion techniques further enhance classification performance, particularly in predicting damage type, underscoring the potential of integrating multiple data sets for comprehensive quality assessment.

Characterization of key aroma-active compounds in Zanthoxylum schinifolium by sensory evaluation and multiple instrumental analyses

The aroma characteristics of Zanthoxylum schinifolium from four different production areas in Sichuan were identified and compared. Aroma components were analyzed via sensory evaluation, gas chromatography–olfactometry–mass spectrometry (GC–O–MS), and comprehensive two-dimensional gas chromatography-olfactometry-mass spectrometry (GC × GC–O–MS). The results revealed that minty, spicy, woody, fresh, citrus, and herbal notes could be perceived, with the Jinyang sample exhibiting the most significant aroma profile. Compared with GC–O–MS, GC × GC–O–MS offers advantages in identifying aroma-active compounds, and it can identify more types and quantities of aroma-active compounds. In this study, 40 aroma-active compounds from seven different classes were identified via GC × GC–O–MS. Through aroma extraction dilution analysis (AEDA), 14 aroma-active compounds were quantitatively analyzed, and odor activity values (OAVs) were calculated. Additionally, orthogonal partial least squares discriminant analysis (OPLS-DA) was employed to identify four aroma-active compounds with variable importance in projection (VIP) scores greater than 1, indicating their potential as identification markers. This study enhances our understanding of the sensory characteristics and aroma-active compounds of Zanthoxylum schinifolium.

Exploring the molecular characteristics of organic matter in low-rank coals using GC×GC/TOF-MS plus data mining

In-depth understanding the form of organic matter in low-rank coals contributes to the clean and efficient utilization of coals. Two low-rank coals were successively dissolved with cyclohexane, acetone and methanol at 300 °C, respectively. Six thermal dissolution (TD) extracts were comparatively analyzed using comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC×GC/TOF-MS). Cyclohexane tends to extract low-polar compounds inherent in coal, such as aliphatic hydrocarbons, arenes and phenols. Acetone can extract monocyclic aromatic hydrocarbons containing alkyl side chains. Meanwhile, acetone can form N-H⋯O hydrogen bonds with nitrogen-containing organic compounds (NCOCs), facilitating the extraction of a greater quantity of NCOCs. Methanol breaks the ArCH2OArR structural unit within coal molecules and forms the dominant alkyl-substituted phenol. It was revealed that sequentially TD at 300 °C using different solvents only breaks intermolecular forces and weak covalent bonds. Additionally, a series of isomers of tricyclic aromatic hydrocarbons and alkylphenols were authenticated by GC×GC/TOF-MS. Principal component analysis and hierarchical clustering analysis were applied to mine effective molecular information from the extensive MS data. The statistical results indicate that solvent had a significant impact on the structure and composition of the TD extracts, more so than the variations in coal species. Thus, the conjunction of GC×GC/TOF-MS and chemometrics provided methodological guidance for an enhanced comprehension of the molecular structure of coals.

Characterization of Key Odor-Active Compounds in Draft Beers for the Chinese Market Using Molecular Sensory Science Approaches.

Beer is a popular alcoholic beverage worldwide. However, limited research has been conducted on identifying key odor-active components in lager-type draft beers for the Chinese market. Therefore, this study aims to elucidate the odor characteristics of the four most popular draft beer brands through a sensory evaluation and an electronic nose. Subsequently, the four draft beers were analyzed through solid-phase microextraction and liquid-liquid extraction using a two-dimensional comprehensive gas chromatography-olfactometry-mass spectrometry analysis (GC×GC-O-MS). Fifty-five volatile odor compounds were detected through GC×GC-O-MS. Through an Aroma Extract Dilution Analysis, 22 key odor-active compounds with flavor dilution factors ≥ 16 were identified, with 11 compounds having odor activity values > one. An electronic nose analysis revealed significant disparities in the odor characteristics of the four samples, enabling their distinct identification. These findings help us to better understand the flavor characteristics of draft beer and the stylistic differences between different brands of products and provide a theoretical basis for objectively evaluating the quality differences between different brands of draft beer.

Characterization and elimination efficiency of volatile organic compounds in mechanically recycled polyethylene terephthalate at various recycling stages

The recycling of polyethylene terephthalate (PET) stands as an effective strategy for mitigating plastic pollution and reducing resource waste. The study aimed to investigate the characterization and elimination efficiency of volatile organic compounds (VOCs) present in rPET at various recycling stages using comprehensive two-dimensional gas chromatography-quadrupole-time-of-flight-mass spectrometry coupled with chemometrics. The results revealed that 52, 135, 95, 44, and 33 VOCs, mostly classified into three chemical groups, were tentatively identified in virgin − PET (v-PET), cold water washed − rPET (C-rPET), decontaminated − rPET (D-rPET), melt-extruded − rPET (M-rPET), and solid-state polycondensation − rPET (S-rPET), respectively. Regarding the VOCs with high and median detection frequencies, fatty acyls showed the highest elimination efficiency (100 % and 92 %), followed by organooxygen compounds (81 % and 99 %), others (97 % and 95 %), and benzene and substituted derivatives (82 % and 95 %) in term of HS-SPME. Following the recycling process, there was a general decrease in the concentration of almost all VOCs, as evidenced by the substantial reduction of o-Xylene, hexanoic acid, octanal, and D-limonene from 18.11, 22.43, 30.74, and 7.41 mg/kg to 0, 0, 3.97, and 0 mg/kg, respectively. However, it was noteworthy that the VOCs identified in the samples were not completely extracted, owing to the limitations of HS-SPME. Furthermore, chemometrics analysis indicated significant discrimination among VOCs from vPET, C-rPET, D-rPET, and M-rPET, while indistinct differences were observed between M-rPET and S-rPET. This study contributes to the enhancement of the recycling process and emphasizes the importance of safeguarding consumer health in terms of elimination of VOCs.

Identification of Bis(methylsulfanyl)methane and Furan-2(5H)-one as Volatile Marker Compounds for the Differentiation of the White Truffle Species Tuber magnatum and Tuber borchii.

Some truffles are expensive and, therefore, are prone to food fraud. A particular problem is the differentiation of high-priced Tuber magnatum truffles from cheaper Tuber borchii truffles, both of which are white truffles with similar morphological characteristics. Using an untargeted approach, the volatiles isolated from samples of both species were screened for potential marker compounds by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) and statistical analysis of the obtained semiquantitative data. Results suggested bis(methylsulfanyl)methane and furan-2(5H)-one as compounds characterizing T. magnatum and T. borchii, respectively. Exact quantitation of both volatiles by conventional one-dimensional gas chromatography-mass spectrometry in combination with stable isotopologues of the target compounds as internal standards confirmed both as marker compounds. The method is suitable to be used in the routine analysis for the objective species differentiation of T. magnatum and T. borchii.

Decoding regional flavor uniqueness of Jiangxiangxing baijiu by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry combined with quantitative descriptive analysis

Establishing a fine quality image through regional typicality is significant to alcoholic beverages, but the concept of region has yet to be established for Jiangxiangxing (JX) baijiu. This study sought to compare chemical and sensory profiles of JX baijiu from different regions and to identify marker volatiles and aromas as regional typicality signatures of JX Baijiu. A total of 395 potential aroma compounds were identified in JX baijiu from different regions, and 121 showed significantly different (p < 0.05, VIP >1). Chemical profiles showed that JX baijiu from Moutai (MT) region with higher levels of pyrazines and furans, which from Northeast (NE) and Xiangchu (XC) regions with higher levels of esters and alcohols, respectively. Sensory profiles revealed that JX baijiu from MT and Chuanqian (CQ) regions were characterized by higher intensity of caramel, roasted, sauce-like, and burnt aromas, which from NE and XC regions were characterized by higher intensity of fruity and floral aromas. The potential relationships between 121 aroma compounds (p < 0.05, VIP >1) and 10 aromas were assessed, which highlighted the chemical basis underlying the unique aroma profile of JX baijiu. The results will contribute to unravel regional uniqueness of JX baijiu through regional flavor images.

Molecular and geochemical characteristics of lignite in different plant sources evaluated using unsupervised analyses

Three lignites were subjected to sequential thermal dissolution using cyclohexane, methanol, and ethanol as the solvent to acquire soluble fractions (SFs). Comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC × GC/TOF MS) was used to separate and reveal complex molecular composition of SFs. Low polar compounds such as chain alkanes (CAs) and arenes were enriched by cyclohexane. Strong polar compounds like phenols were concentrated by methanol, and partial phenols and CAs were also detected in the ethanol extracts. Meanwhile, organic nitrogen compounds (ONCs) and organic sulfur compounds (OSCs) such as pyridines, quinolines and thiophenes were identified in SFs. In all SFs, pyridines have the highest relative abundance, followed by quinolines compared with other ONCs, and thiophenes were only detected in cyclohexane and methanol SFs. In addition, halogen-containing compounds reflecting the geochemical characteristics of lignite were also detected, and their total relative abundances were 0.544%, 1.591% and 5.101% in the SFs of Shengli (SL), Xiheishan (XHS), and Xiaolongtan (XLT), respectively, which provided evidence for the evolution of coal. Two unsupervised analysis methods, hierarchical cluster analysis and principal components analysis, were efficient in clustering components according to molecular characteristics, and visualized detailed similarities and differences among the compounds in SFs.

A new strategy to study geochemical characteristics and migration of crude oils in Zhu I Depression, Pearl River Mouth Basin, South China Sea

Oxygen- and sulfur-containing compounds were proved to be good alternatives to pyrrolic nitrogen compounds in the study of oil migration. To promote the detectability of complex and trace analytes, a simple and efficient device, gas purge microsyringe extraction (GP-MSE), was developed and combined with comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC × GC-TOFMS) for the simultaneous analysis of target compounds. Oil samples were collected from the Zhu I Depression of the Pearl River Mouth Basin in the South China Sea and classified into three groups in terms of geochemical distribution characteristics, parameters and concentrations of carbon isotopes, alkanes, diamondoids, terpanes and steranes. Based on nitrogen-, sulfur- and oxygen-containing compounds, the general oil filling into the Zhu Ⅰ Depression was determined from the central sags southward to the Dongsha Uplift. Faults provide pathways for vertical migration and delta sandstones served as the main lateral and long-distance regional migration pathways. The molecular dynamics (MD) simulation provides a nanoscale perspective into geochromatographic fractionation, which is generated mainly by the interaction between polar compounds and clay minerals. In MD simulations, the binding affinity of carbazole, dibenzothiophene and dibenzofuran on clay minerals is higher than that on non-clay minerals due to the available active sites on the surface of clay minerals for the formation of electrostatic and van der Waals interaction. Carbazole, dibenzothiophene and dibenzofuran achieve adsorption stability in a parallel manner on chlorite and kaolinite, whereas on illite, adsorption stability is achieved in tilted manner. Based on the adsorption energies, kaolinite shows the highest adsorption affinity, whereas calcite exhibits the lowest adsorption affinity. Microcline even demonstrates a noticeable repulsive effect. The geochromatographic fractionation effect seems to be not controlled only by the affinity between oil composition and clay mineral during oil migration.

Chemical evaluation of pyrolysis oils from domestic and industrial effluent treatment station sludges with perspective to produce value-added products

The use of renewable sources for energy has increased due to the high demand of modern society and the environmental impacts caused by the use of fossil fuels. Environmentally friendly renewable energy production may involve thermal processes, including the application of biomass. We provide a comprehensive chemical characterization of sludges from domestic and industrial effluent treatment stations, as well as the bio-oils produced by fast pyrolysis. A comparative study of the sludges and the corresponding pyrolysis oils was performed, with characterization of the raw materials using thermogravimetric analysis, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, elemental analysis, and inductively coupled plasma optical emission spectrometry. The bio-oils were characterized using comprehensive two-dimensional gas chromatography/mass spectrometry that identified compounds classified according to their chemical class, mainly related to nitrogenous (62.2%) and ester (18.9%) for domestic sludge bio-oil, and nitrogenous (61.0%) and ester (27.6%) for industrial sludge bio-oil. The Fourier transform ion cyclotron resonance mass spectrometry revealed a broad distribution of classes with oxygen and/or sulfur (N2O2S, O2, and S2 classes). Nitrogenous compounds (N, N2, N3, and NxOxclasses) were also found to be abundant in both bio-oils, due to the origins of the sludges (with the presence of proteins), making these bio-oils unsuitable for use as renewable fuels, since NOxgases could be released during combustion processes. The presence of functionalized alkyl chains indicated the potential of the bio-oils as sources of high added-value compounds that could be obtained by recovery processes and used for the manufacture of fertilizers, surfactants, and nitrogen solvents.

Comparison of two data processing approaches for aroma marker identification in different distilled liquors using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry dataset.

Whisky, brandy, rum, and Chinese baijiu are popular distilled spirits globally, and the volatile components play an essential role in the aroma of these distilled liquors. Volatile compounds in whisky, brandy, rum, and three main aroma types of Chinese baijiu (strong, light, and sauce) were investigated using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS). Two significant variable detection approaches, the variable importance in the projection (VIP) and nonparametric test (Mann-Whitney U test), were compared to determine the volatile markers among these samples. It was found that the VIP model was more efficient in screening significant variants than the U test. A total of 117 common markers were selected by both the VIP and U test methods with potential aroma contributions. Esters and acids were the main aroma markers for baijiu, diethyl esters were the main aroma markers for brandy, whereras pyrazines, lactones, and furans were the main aroma markers for whisky. Based on the chosen markers, different unknown distilled liquors were successfully classified in the model validation. This study provided a feasible methodology for spirit sample speculation based on volatile composition obtained by GC×GC-TOFMS.

Discovery and Flavor Characterization of High-Grade Markers in Baked Green Tea

Green tea is a popular beverage around the world and possesses a unique flavor. The flavor qualities of green tea are closely related to its grade and this relationship has not yet been studied. Three baked green teas with similar flavor were studied, namely, Huangshan Maofeng, Taiping Houkui, and Shucheng Xiaolanhua. A total of 34 odor compounds were identified by solid phase microextraction (SPME) combined with two-dimensional comprehensive gas chromatography-olfactometry-mass spectrometry analysis (GC×GC-O-MS). The results of the clustering analysis showed that the content of D-limonene and linalool in the high-grade (Grade A) tea was much higher than the content in other grades, so they were identified as odor markers of Grade A baked green tea. The taste components of different grades of green tea infusion were analyzed by high-performance liquid chromatography-mass spectrometry (HPLC-MS) and HPLC. A combination of clustering analysis, principal component analysis (PCA), and orthogonal partial least squares discrimination analysis (OPLS-DA) indicated that galloylglucose, digalloylglucose, trigalloyglucose, strictinin, and gallic acid could be used as taste markers of Grade A baked green tea. Therefore, the results in this paper reveal the substances responsible for the odor and taste markers of high-grade baked green tea.

One-dimensional and comprehensive two-dimensional gas chromatographic approaches for the characterization of post-consumer recycled plastic materials

In September 2022, the European Commission published its new regulation on recycled plastic materials for food contact. It allows newly developed, non-authorized technologies and approaches, or so-called novel technologies, to be deployed in the field to generate the data needed for establishing regulatory and/or fit for purpose processes. The data shall be generated by using suitable methods, but the regulation does not give a more detailed description on those. In this study, commercially purchased buckets made of post-consumer recycled polypropylene were screened, using a number of different analytical approaches. Sample preparation methods, analysis techniques, and the data and information generated were compared. The results clearly demonstrate the need for a detailed characterization of such materials and the advantages and disadvantages of the analysis using conventional gas chromatography with flame ionization detection and mass spectrometery as well as two-dimensional comprehensive gas chromatography with time of flight mass spectrometry.Graphical

The Fishy Off-Odor Removal and Umami Enhancing Effect of Enzymatic Hydrolysis of Fish By-Products by Proteases

ABSTRACT The aim was to study the changes in flavor compounds hydrolyzed by different proteases in fish soup boiled with fish scraps The odor compounds were extracted by solid-phase microextraction (SPME) and analyzed by two-dimensional comprehensive gas chromatography-olfactometry-mass spectrometry (GC×GC-O-MS). The state of the distribution of free amino acids, 5’-nucleotides, peptides and equivalent umami concentration (EUC) were investigated. It was found that enzymatic hydrolysis significantly reduced off-flavor compounds, and the umami taste increased significantly. The synergistic effect between FlavourzymeTM and ProtamexTM (F-P) made the flavor of enzymatic hydrolysis better than that of other enzymes.

Volatile flavour identification and odour complexity of radix Angelicae sinensis by electronic nose, integrated gas chromatography-mass spectrometry/olfactometry and comprehensive two-dimensional gas chromatography-time-of-flight-mass spectrometry.

Radix Angelicae sinensis (Danggui, DG) is known as one of the typical traditional Chinese medicines. DG material consists of a variety of volatile substances, polysaccharides, organic acids, ceramides, amino acids, vitamins, microelements, among others, and thus has been used for medicinal and edible purposes in a long history. The fragrance is of importance to assessing the DG material quality. This study was to determine volatile flavour compositions of DG materials and to reveal the odour complexity. Electronic nose (E-nose), integrated gas chromatography-mass spectrometry/olfactometry (GC-MS/O) and comprehensive two-dimensional gas chromatography-time-of-flight-mass spectrometry (GC × GC-TOF-MS), combined with solid-phase micro-extraction (SPME), were mainly used to address the flavour complexity of DG materials. Using the E-nose sensor responses, a total of 105 batches of DG samples cultivated in six provinces of China were categorised according to their odour differentiations, and a principal component analysis (PCA) model was established for evaluating the sample quality through a combination of Hotelling's T2 and Q-residual values in a statistical quantitative sense. By the GC-MS/O and GC × GC-TOF-MS analyses, 196 volatile flavour compounds were identified, 51 odour-active areas discerned and 39 odourants determined. It was terpenes and aromatics of the flavour compounds that mainly contributed to the odour attributes of DG herb. The SPME-GC × GC-TOF-MS method was the first time employed to analyse the volatile flavours of DG materials, and thus made a breakthrough in determining 196 flavour compounds, much more than those in any previous report. The work also made a significant step forward to link the flavour compositions and odour complexity of radix Angelicae sinensis by E-nose and GC-MS/O techniques. It not only provided a statistical PCA model that did not depend on any predetermined compositions or sensory properties for, but also a comprehensive insight into the quality evaluation of DG materials.

Research on the chemical composition of Mentha haplocalyx volatile oils from different geographical origins by comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry in combination with principal component analysis and the enrichment of bioactive compounds by particle-assisted solvent sublation

The chemical composition of Mentha haplocalyx volatile oils from different origins was studied by gas chromatography/mass spectrometry (GC/MS) and comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC × GC/TOFMS). A total of 67 compounds were identified by GC/MS and a total of 1956 compounds were identified by GC × GC/TOFMS from five Mentha haplocalyx samples in different origins. In the GC × GC/TOFMS chromatogram, the classification of group type could be clearly observed. The results of GC × GC/TOFMS showed that there were some significant differences in chemical composition of Mentha haplocalyx between Anhui and other geographically areas, especially the biologically active ingredient of Isopiperitone, Levomenthol and Isomenthone. They were more abundant from Anhui than that from other origins. Principal component analysis (PCA) of GC/MS and GC × GC/TOFMS data was performed. The results showed that the PCA model constructed with the data of GC × GC/TOFMS was better than that of GC/MS to identify the authenticity of Mentha haplocalyx medicinal materials. Using the particle-assisted solvent flotation method, the active compounds were enriched from Mentha haplocalyx samples, which could be further used for food additive or pharmacological activity research.

Comparative evaluation of physical characteristics and volatile flavor components of Bangia fusco-purpurea subjected to hot air drying and vacuum freeze-drying

Bangia fusco-purpurea is an economically important seaweed with Fujian characteristics. Given that its harvest is seasonal, drying is often used to remove moisture, extend storage time, and facilitate further processing. Hence, the current study sought to explore the impact of different drying processes on the quality and volatile fingerprints of Bangia fusco-purpurea. To this end, the effects of hot air drying (HAD) and vacuum freeze drying (VFD) on the drying characteristics, microstructure, rehydration, and volatile components of dried B. fusco-purpurea were investigated. The results showed that the water removal efficiency of HAD was significantly higher than that of VFD. However, VFD better preserved the skeletal structure of B. fusco-purpurea than HAD, with a faster rehydration rate and a more uniform cell structure after rehydration. Using electronic nose and comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOF MS), significant differences in the volatile profiles of fresh, HAD, and VFD B. fusco-purpurea were assessed. E-nose analysis revealed that both HAD and VFD treatments significantly reduced sulfides, aromatic compounds, and nitrogen oxides in fresh B. fusco-purpurea. However, the alcohol, aldehyde, and ketone contents were lower in the VFD samples compared with HAD and fresh samples, whereas the content of methyl flavor substances was significantly higher. GC × GC-TOF MS analysis revealed that the most abundant volatile categories in HAD and VFD were hydrocarbons, alcohols, and esters. The number of volatile components in the HAD samples was significantly lower than in the VFD and fresh samples. As drying progressed, hydrocarbons and alcohols were formed in dried B. fusco-purpurea due to the thermal degradation of carbohydrates, lipids, amino acids, and the Maillard reaction. There were also significant flavor differences between HAD and VFD B. fusco-purpurea. Thus, although HAD exhibits better drying efficiency, VFD has more significant advantages in terms of product quality.

Comparison of aroma active compounds in cold- and hot-pressed walnut oil by comprehensive two-dimensional gas chromatography-olfactory-mass spectrometry and headspace-gas chromatography-ion mobility spectrometry

Aroma composition of cold-pressed walnut oil (CWO) and hot-pressed walnut oil (HWO) was analyzed by comprehensive two-dimensional gas chromatography-olfactory-mass spectrometry (GC × GC-O-MS) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). A total of 83 and 197 compounds were identified in the CWO and HWO, respectively; among these, 76 and 123 compounds were sniffed exclusively by GC × GC-O-MS, respectively. A total of 36 volatile compounds were detected by HS-GC-IMS, of which 10 in CWO and 32 in HWO. Based on of flavor dilution (FD) factors, odor-activity values (OAVs), and recombination and omission experiments, 1-octen-3-ol, cyclohexanol, and benzaldehyde were found to be the key aroma-active compounds in CWO, while 3-methylbutanal, (E,E)-2,4-nonadienal, nonanal, 1-octen-3-ol, 3-pentanol, 1-octanol, and furfural were the key aroma-active compounds in HWO. Moreover, Maillard reaction and lipid oxidation were found to play an important role in flavor formation in HWO. This study provides a guide to improve the quality of walnut oil based on aroma characteristics.

Chemometrics-assisted analysis of chemical impurity profiles of tabun nerve agent using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

A route determination strategy through non-targeted screening of chemical attribution signatures was developed to identify tabun samples from three different synthetic routes. The CAS profiles of tabun samples were obtained by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometer (GC×GC-TOFMS). The structures of 109 CAS were identified by NIST library and mass spectrometry fragment analysis. A few identified compounds could be traced to impurities in precursor compounds used in tabun synthesis. Based on the gas chromatography/mass spectrometry peak data of the selected CAS, partial least squares-discriminant analysis (PLS-DA) was used to extract the chemical attribution signatures of the characteristic compounds. The trained PLS-DA model performed well, with the lowest specificity and sensitivity values of 1.000 and 0.882, respectively. The performance of the PLS-DA model was further verified by unknown sample test set. The model demonstrated its ability to differentiate all the unknown tabun samples. The stability of chemical attribution signatures from different time periods was also investigated, and was further evaluated.