A chestnut-like aroma is widely considered an important indicator of an excellent-quality green tea; however, the key odorants responsible for chestnut-like aroma have never been systematically ...studied and remain unknown. In this study, the aroma components of green teas and Chinese chestnuts were analyzed using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS), and 58 compounds were identified as common aroma components among green teas, boiled Chinese chestnuts, roasted Chinese chestnuts and raw Chinese chestnuts. Subsequently, 17 volatiles, including 3-methylbutanal, (E)-3-penten-2-one, ethylbenzene, heptanal, benzaldehyde, 2-pentylfuran, octanal, benzeneacetaldehyde, (E)-2-octenal, (E,E)-3,5-octadien-2-one, linalool, nonanal, (E)-2-nonenal, decanal, (Z)-hex-3-en-1-yl hexanoate, trans-β-ionone and (E)-nerolidol, were identified as the key odorants responsible for chestnut-like aroma based on the odor activity value (OAV) calculation method. Besides, the comparison of OAVs of key odorants between fresh tea leaves and finished teas indicated that all key odorants were present in fresh tea leaves and that their contents increased or decreased during tea processing. Moreover, the comparison between results of OAV and gas chromatography-olfactometry (GC-O) methods showed that ethylbenzene, heptanal, benzaldehyde, 2-pentylfuran, (E,E)-3,5-octadien-2-one, linalool, (Z)-hex-3-en-1-yl hexanoate and trans-β-ionone were the common identified compounds between the two methods. The identification of chestnut-like aroma in green teas will provide a theoretical basis for further research on the directional adjustment and control of tea aroma quality.
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•Volatiles of green teas and Chinese chestnuts were analyzed by GC × GC-TOFMS.•58 Compounds were identified as potential key odorants by statistical comparison.•17 Key odorants were determined by OAV calculation and validation analysis.•Key odorants showed different variation trends of contents during processing.•The GC-O analysis of green tea with chestnut-like aroma was performed.
•Sensory and chemical profiles of strong-aroma type Baijiu from different regions.•58 compounds were identified as potential markers of regional strong-aroma type Baijiu.•Relationships between ...potential aroma compounds and sensory attributes were shown.
Comprehensive 2D gas chromatography–time-of-flight mass spectrometry was combined with descriptive sensory analysis to elucidate the specificity of strong-aroma type Baijiu (Chinese liquor) from different regions, based on regionally distinct flavor characterized by chemical and sensory profiles. Numerous potential aroma compounds (262) were identified, among which 58 aroma compounds were significantly different between the samples from Sichuan and Jianghuai regions. Relationships between these potential aroma compounds and sensory attributes were investigated by partial least squares regression and network analysis. The compounds that dominantly contributed to the important sensory attributes were identified. The high pyrazines, furanoids, and carbonyls amounts contributed to the high intensities of the cellar, toasted, and grain aroma profiles of the Sichuan region samples, while the high ester and alcohol levels contributed to the fruity and floral aroma profiles of the Jianghuai region samples. This approach may have practical application in flavor characterization of other alcoholic beverages.
•Improved simplicity and accuracy of analysis of maleimides by GC×GC-ToF-MS.•High sensitivity of the method enabled detection of new compounds.•Previous erroneous quantification due to coelution ...discovered.•Enable studies on environmental significance of chlorophyll degradation products
Maleimides (1H-Pyrrole-2,5-diones) are monopyrrolic pigment derivatives with specific alkyl side chains that can be directly linked to their tetrapyrrole precursors, most notably chlorophylls and bacteriochlorophylls. These compounds can be used as palaeoenvironmental indicators such as algal productivity and redox conditions in ancient and modern aquatic systems. Here, we present a new method using two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-ToF-MS), which enables the rapid analysis of maleimides in complex mixtures and different matrices (e.g. sediments and soils), therefore largely simplifying the previous intricate maleimide purification protocol. This method also reduces the potential for bias associated with partial losses due to low recovery and the high volatility of maleimides. The maleimide distributions and concentrations obtained by GC×GC-ToF-MS were reproducible and in agreement with the previously used purification procedure followed by analysis with traditional gas chromatography–mass spectrometry (GC–MS). The new method also resolved previously unrecognised, partial coelution of some maleimides with unknown compounds by quantification with the m/z 75 fragment ion. Furthermore, the higher sensitivity enabled the detection of previously unrecognised and preliminarily identified maleimides based on their relative retention times. The new, easier, rapid and more sensitive GC×GC-ToF-MS method greatly facilitates the analysis of maleimides in environmental samples to study tetrapyrrole degradation processes and will further the development of maleimides as biomarkers for palaeoenvironmental reconstructions.
Little is known about the impact of emissions of micropollutants from small and large-scale sewage treatment plants (STPs) on drinking water source areas. We investigated a populated catchment that ...drains into Lake Mälaren, which is the drinking water source for around 2 million people including the inhabitants of Stockholm, Sweden. To assess the persistence, mobility, bioavailability and bioaccumulation of 32 structurally diverse emerging organic contaminants, sediment, integrated passive and grab water samples were collected along the catchment of the River Fyris, Sweden. The samples were complemented with STP effluent and fish samples from one sampling event. Contaminants identified as persistent, mobile, and bioavailable were 4,6,6,7,8,8-hexamethyl-1,3,4,7-tetrahydrocyclopentagisochromene (galaxolide), 2,4,7,9-tetramethyl-5-decyn-4,7-diol, tris(2-chloro-ethyl) phosphate, tris(1,3-dichloro-2-propyl) phosphate, and tris(1-chloro-2-propyl) phosphate. Galaxolide and 2,4,7,9-tetramethyl-5-decyn-4,7-diol were additionally found to be bioaccumulative, whereas n-butylbenzenesulfonamide was found to be only persistent and mobile. The total median mass flux of the persistent and mobile target analytes from Lake Ekoln into the drinking water source area of Lake Mälaren was estimated to be 27kg per year. Additionally, 10 contaminants were tentatively identified by non-target screening using NIST library searches and manual review. Two of those were confirmed by reference standards and further two contaminants, propylene glycol and rose acetate, were discharged from STPs and travelled far from the source. Attenuation of mass fluxes was highest in the summer and autumn seasons, suggesting the importance of biological degradation and photodegradation for the persistence of the studied compounds.
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•The fate of organic wastewater contaminants was tracked along a river transect.•Five persistent, mobile and bioavailable contaminants were identified.•Two persistent and mobile contaminants were additionally found in fish.•All five contaminants were found in a lake used as a drinking water reservoir.•The majority of contaminants originated from sewage treatment plant effluent.
Commercial chlorinated paraffins (CPs) are a source of CPs in the environment, and clarification of the different CP groups present in commercial products is important for source characterization. ...Resolving CP congener groups is hindered by the complex CP compositions of commercial products. We used comprehensive two-dimensional gas chromatography coupled with electron capture negative ionization high-resolution time-of-flight mass spectrometry to profile 57 C8 − C17 CP congener groups in 18 CP-42, CP-52, and CP-70 commercial products. Very short-chain CPs (vSCCPs), including C8Cl5–8 and C9Cl5–9 CPs, and other chlorinated aromatic compounds were identified in the commercial products. The mass fractions of total vSCCPs, short-chain CPs (SCCPs) and medium-chain CPs (MCCPs) in the commercial products ranged from 0.02% to 3.61%, 0.75% to 51.4%, and 0.39% to 69.1%, respectively. Two-dimensional hierarchical cluster analysis with a heat map plot highlighted variations in the C8 − C17 CP congener group patterns among different commercial CP formulations. The principal component analysis results indicated that commercial CPs products might be important contributors to vSCCPs, SCCPs, and MCCPs in various environmental matrices. This study provides comprehensive and well-resolved compositional data for CPs in commercial products, which will be helpful for CP source characterization.
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•Mass fractions and profiles of 57 C8 − C17 CPs were resolved by GC × GC–ECNI-HRTOFMS.•vSCCPs including C8Cl5–8 and C9Cl5–9 CPs were identified in commercial products.•C8 − C17 CP congener group abundances varied among different CP-52 products.•Source association of C8 − C17 CPs were found between CP-52 and environment samples.
Furans is a versatile chemical family, developing environmental-friendly methods to prepare furans and enhance the selectivity of high-value furans are of great significance. In present study, ...bio-based activated carbon supported Al-containing bimetals were devised to serve as solid acid catalysts for selective transformation lignocellulosic biomass and its components into valuable furans. Among the bimetallic catalysts, 2Al-4Zr/AC increased both the content of furans and the selectivity of 5-methylfurfural (5-MFF) , and the highest peak area% of furans and selectivity of 5-MFFwere 88.6% and 44.5%, which were derived from the catalytic pyrolysis of glucose, and the counterparts from the catalytic pyrolysis of pine wood were 56.3% and 30.7%, respectively. In addition to 5-MFF, 2-methylfuran (2-MF), furfural (FF) and 2,5-dimethylfuran (DMF) were also included into major furans. In the catalytic pyrolysis process of lignocellulosic biomass, C6-based sugars were conducive to the production of 5-MFF, and C5-based sugars favored the formation of 2-MF and FF. Characterization with NH3-TPD, Pyridine-IR, N2 adsorption-desorption, XRD and XPS indicated that 2Al-4Zr/AC, with mild Lewis acidity and combined Brønsted acid sites, high surface area and micro-mesoporous structure, promoted both the dehydration of saccharides and the dehydrogenation of cyclopentanones to increase the content of furans. In the catalyst, the synergistic effect between Al species (including Al2O3, AlO(OH) and Al(OH)3) and Zr species (mainly ZrO2) played an important role in its catalytic activity, and Al species were the major contributor to its activity.
2Al-4Zr/AC selectively convert lignocellulosic biomass into value-added furans, mainly 5-MFF, 2-MF and FF, and C6-based sugars favored the selectivity of 5-MFF, and C5-based sugars were conducive to the selectivity of 2-MF and FF. Display omitted
•Catalytic activities of various Al-based bimetals were investigated.•Synergy between Al species and Zr species were evaluated.•2Al-4Zr/AC achieved the content of furans as 88.6% with 44.5% selectivity of 5-MFF.•The possible pathways on the formation of furans were proposed.•Experiments were carried out using Py-GC × GC/MS.
Mineral oil hydrocarbons (MOH) contain a wide structural diversity of molecules, for which the reference method of analysis is the online coupled liquid chromatography-gas chromatography with flame ...ionization detection (LC-GC-FID). These compounds are very heterogeneous from a toxicological viewpoint, and an accurate risk assessment when dealing with a MOH contamination can only be performed if sufficient information is available on the types of structures present (i.e., number of carbons, degree of alkylation, number of aromatic rings). Unfortunately, the separation performances of the current LC-GC-FID method are insufficient for such characterization, not even mentioning the possible coelution of interfering compounds which additionally hinder MOH determination. Comprehensive two-dimensional gas chromatography (GC × GC), while mostly used for confirmation purposes in the past, starts to prove its relevance for overcoming the weaknesses of the LC-GC method and reaching even better the analytical requirements defined in the latest EFSA opinion. The present paper therefore aims at highlighting how GC × GC has contributed to the understanding of the MOH topic, how it has developed to meet the requirements of MOH determination, and how it could play a role in the field for overcoming many of the current analytical and toxicological challenges related to the topic.
The analysis of aroma composition in scented plants and natural products to probe their quality and safety is an important topic, particularly when such ingredients are intended for long term use as ...in food or cosmetic products. The development of fast, comprehensive, and effective analytical tools for essential oil analysis in such complex mixtures is of interest and moreover when present in blend of several oils, as typical in case of nutraceuticals or cosmetics. Comprehensive studies of volatiles could be achieved via coupling the separation power of multidimensional chromatography with selective detectors as mass spectrometers. This strategy enables high-throughput and global analysis of hundreds of metabolites in a single step. Different multidimensional setups such as GC × GC and LC-GC in addition to various chemometric approaches applied for essential oils analysis form a fundamental part of this review. Asides, applications of multidimensional chromatography for essential oils chemotyping, enantio-separation, quality control and adulteration detection in the different matrices are also presented.
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•Multidimensional chromatography MDC have led to advances in essential oils analysis.•Principles and novel approaches of MDC for essential oils analysis are presented.•Bioinformatics employed for data visualization from multidimensional analysis are reviewed.•MDC applications for essential oils analysis in food, cosmetics and medicine.
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•A new method for measuring orthogonality in multidimensional separations is introduced.•Our method also diagnoses areas where peaks are clustered in the separation space.•The new ...method comprises of a number of equations which are easily implemented in Microsoft Excel.•We applied the method to 8 computer-generated and 2 experimental multidimensional chromatograms.•The method compared favorably against established methods.
Multi-dimensional chromatographic techniques, such as (comprehensive) two-dimensional liquid chromatography and (comprehensive) two-dimensional gas chromatography, are increasingly popular for the analysis of complex samples, such as protein digests or mineral oils. The reason behind the popularity of these techniques is the superior performance, in terms of peak-production rate (peak capacity per unit time), that multi-dimensional separations offer compared to their one-dimensional counterparts. However, to fully utilize the potential of multi-dimensional chromatography it is essential that the separation mechanisms used in each dimension be independent of each other. In other words, the two separation mechanisms need to be orthogonal. A number of algorithms have been proposed in the literature for measuring chromatographic orthogonality. However, these methods have their limitations, such as reliance on the division of the separation space into bins, need for specialist software or requirement of advanced programming skills. In addition, some of the existing methods for measuring orthogonality include regions of the separation space that do not feature peaks. In this paper we introduce a number of equations which provides information on the spread of the peaks within the separation space in addition to measuring orthogonality, without the need for complex computations or division of the separation space into bins.
The method of headspace coupled with comprehensive two‐dimensional GC–time‐of‐flight MS (HS‐GC × GC–TOF/MS) was applied to differentiate the volatile flavor compounds of three types of pure vegetable ...oils (sesame oils, peanut oils, and soybean oils) and two types of adulterated oils (sesame oils and peanut oils adulterated with soybean oils). Thirty common volatiles, 14 particular flavors and two particular flavors were identified from the three types of pure oils, from the sesame oils, and from the soybean oils, respectively. Thirty‐one potential markers (variables), which are crucial to the forming of different vegetable oil flavors, were selected from volatiles in different pure and adulterated oils, and they were analyzed using the principal component analysis (PCA) and cluster analysis (CA) approaches. The samples of three types of pure vegetable oil were completely classified using the PCA and CA. In addition, minimum adulteration levels of 5 and 10% can be differentiated in the adulteration of peanut oils and sesame oils with soybean oils, respectively.
Practical applications: The objective was to develop one kind of potential differentiated method to distinguish high cost vegetable oils from lower grade and cheaper oils of poorer quality such as soybean oils. The test result in this article is satisfactory in discriminating adulterated oils from pure vegetable oils, and the test method is proved to be effective in analyzing different compounds. Furthermore, the method can also be used to detect other adulterants such as hazelnut oil and rapeseed oil. The method is an important technical support for public health against profit‐driven illegal activities.
HS coupled with GC × GC–TOF/MS was applied to the determination of the volatile compounds of three pure vegetable oils (sesame oils, peanut oils, and soybean oils) and two adulterated oils (soybean oils adulteration in sesame oils and peanut oils). The PCA and CA were applied to the analysis of the variables data including 31 potential markers (variables) which were the crucial components during the forming process of different vegetable oils flavor. With the proposed method, the minimum adulteration levels of 5 and 10% can be differentiated in the adulteration of peanut oils and sesame oils with soybean oils, respectively.
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