Average mass scan of the total ion chromatograms: A new gas chromatography–mass spectrometry derived variable for fast and reliable multivariate statistical treatment of essential oil compositional data

Insight into the Characterization of Volatile Compounds in Smoke-Flavored Sea Bass (Lateolabrax maculatus) during Processing via HS-SPME-GC-MS and HS-GC-IMS

The present study aimed to ascertain how the volatile compounds changed throughout various processing steps when producing a smoke-flavored sea bass (Lateolabrax maculatus). The volatile compounds in different production steps were characterized by headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). A total of 85 compounds were identified, and 25 compounds that may be considered as potential key compounds were screened by principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA). Results indicated that aldehydes were the major volatile compounds throughout the processing. The characteristic volatile compound in fresh samples was hexanol, and curing was an effective method to remove the fishy flavor. The concentration of volatile compounds was significantly higher in dried, smoked, and heated samples than in fresh and salted samples. Aldehydes accumulated because of the drying process, especially heptanal and hexanal. Smoke flavoring was an important stage in imparting smoked flavor, where phenols, furans and ketones were enriched, and heating leads to the breakdown of aldehydes and alcohols. This study will provide a theoretical basis for improving the quality of smoke-flavored sea bass products in the future.

Variability in the Chemical Composition of a New Aromatic Plant Artemisia balchanorum in Southern Russia

Lemon wormwood Artemisia balchanorum was recently introduced to southern Russia as a new aromatic plant. Based on biological and chemical characteristics, several populations with dominant citral, linalool, and geraniol production were selected for further development and maintained by seed propagation. Chemical analysis of five outstanding populations at three stages of annual development: vegetative, flower buds, and full flowering, confirmed that the seed populations retain the distinct dynamics of the dominant and minor components during the annual cycle and can be used for the commercial production of citral, linalool, and geraniol. Micropropagation in vitro allows for efficient clonal micropropagation and mass reproduction of elite cultivars and promising forms of A. balchanorum on a commercial scale but cannot serve as a source of direct and efficient production of secondary metabolites.

Data handling and data analysis in metabolomic studies of essential oils using GC-MS

Gas chromatography electron impact ionization mass spectrometry (GC-EI-MS) has been, and remains, the most widely applied analytical technique for metabolomic studies of essential oils. GC-EI-MS analysis of complex samples, such as essential oils, creates a large volume of data. Creating predictive models for such samples and observing patterns within complex data sets presents a significant challenge and requires application of robust data handling and data analysis methods. Accordingly, a wide variety of software and algorithms has been investigated and developed for this purpose over the years. This review provides an overview and summary of that research effort, and attempts to classify and compare different data handling and data analysis procedures that have been reported to-date in the metabolomic study of essential oils using GC-EI-MS.

A new longipinane ketone from Achillea abrotanoides (Vis.) Vis.: chemical transformation of the essential oil enables the identification of a minor constituent

INTRODUCTION

Minor plant constituents are difficult to identify due to the challenging isolation and acquiring of reliable spectral data. Essential oils abound in such minor constituents that might be of high importance for their (e.g. olfactory) properties. The presence of new minor constituents is usually inferred from gas chromatography mass spectrometry (GC-MS) analyses that provide only a mass spectrum and retention data, which are insufficient to allow a positive identification.

OBJECTIVE

To identify a minor unknown constituent of the essential oil of Achillea abrotanoides (Vis.) Vis. (Asteraceae).

METHODOLOGY

The application of chemical transformations (oxidation and reduction) performed directly on crude essential-oil samples, followed by preparative chromatography and detailed spectral analysis, to identify a new longipinane ketone from the mentioned sample.

RESULTS

GC-MS analyses of the essential oil revealed, among other constituents, the presence of a known rare longipinane alcohol (α-longipinen-7β-ol) representing 2.5% of the total GC-peak areas, and a related unidentified oxygenated sesquiterpene (3.8%). Interpretation of their mass spectra led to an assumption that the unidentified one could represent α-longipinen-7-one. Oxidation of the entire essential-oil sample by pyridinium chlorochromate confirmed the assumed relationship among the compounds and gave a simplified enriched mixture containing the ketone (ca. 16%). A straightforward chromatographic separation of the ketone was followed by corroboration of its structure by nuclear magnetic resonance (NMR) (one- and two-dimensional), infrared (IR) and MS.

CONCLUSIONS

The complementing use of chemical transformations of crude essential oils, chromatographic separations, and detailed spectral analysis could have a more general application in the identification of new natural products.

Working with log-ratios

Instrumental signals of samples cannot be compared and/or analysed directly if their concentrations are unknown. Differences in overall concentration need to be removed at the data normalization step. The choice of normalization method has a profound effect on the final results of data analysis, and especially on biomarker identification. One of the possible approaches to deal with the 'size effect' is to work with size-irrelevant (log) ratios instead of the original variables. In the presented study, the performance of log-ratio methods, namely pairwise log-ratio (plr) and centered log-ratio (clr), is discussed for real and simulated data sets with different characteristics. It was found that the clr method can lead to distribution of local differences along an entire signal and as such, it should be avoided in all studies aiming to identify biomarkers.

Methyl 3-(5-(prop-1-yn-1-yl)thiophen-2-yl)propanoate: A Rare Acetylene Derivative from Artemisia absinthium Root Essential Oil

Methyl 3-(5-(prop-1-yn-1-yl)thiophen-2-yl)propanoate (1), biosynthetically and structurally related to dehydromatricaria ester, was isolated from the root essential oil of Artemisia absinthium L. (0.7% of the total oil). This is the second record of this compound and the very first one regarding it as an essential-oil constituent. In this paper, we give details regarding its isolation, structural elucidation and gas chromatographic properties (RI on DB-5 MS column: 1694). The NMR-based identification of the compound was corroborated by simulation of its 1H- and 13C-NMR spectra using a GIAO method (DFT level of theory). A tentative biosynthetic pathway, possibly leading to this compound, is also proposed.

New volatile sulfur-containing compounds from wild garlic (Allium ursinum L., Liliaceae)

In many countries, the leaves of Allium ursinum L. (Liliaceae) are a popular substitute for garlic and, for centuries, the herb has been taken internally to treat an array of medical conditions. Herein, we report the chemical composition of 12 different A. ursinum essential-oil samples (five populations; fresh/air-/oven-dried plant material; leaves/inflorescences). GC-MS/GC-FID analyses, quantitative structure-property relationship modeling (simple 0D/1D-descriptors) of retention indices and the synthesis of selected compounds, enabled the identification of >200 different constituents, mainly organo(poly)sulfides. Some of these were new compounds (allyl (methylthio)methyl, (methylthio)methyl (Z)/(E)-1-propenyl and allyl 1-(methylthio)propyl disulfides) or were previously not detected in samples of natural origin (heptyl methyl, methyl octyl, allyl hexyl (1), allyl octyl (2) and propyl (propylthio)methyl sulfides). A multivariate statistical analysis revealed the onset of significant changes in the plant material volatile profile during the drying process.

(Un)targeted metabolomics in Asteraceae: probing the applicability of essential-oil profiles of senecio L. (Senecioneae) taxa in chemotaxonomy

The possible applicability of (un)targeted metabolomics (volatile metabolites) for revealing taxonomic/evolutionary relationships among Senecio L. species (Asteraceae; tribe Senecioneae) was explored. Essential-oil compositional data of selected Senecio/Senecioneae/Asteraceae taxa (93 samples in total) were mutually compared by means of multivariate statistical analysis (MVA), i.e., agglomerative hierarchical clustering and principal component analysis. The MVA input data set included the very first compositional data on the essential oil extracted from the aerial parts of S. viscosus L. as well as on four different Serbian populations of S. vernalis Waldst. & Kit. (oils from aerial parts and roots; eight samples in total). This metabolomic screening of Senecio/Senecioneae/Asteraceae species (herein presented results and data from the literature) pointed to short-chain alk-1-enes (e.g., oct-1-ene, non-1-ene, and undec-1-ene), with up to now restricted general occurrence in Plantae, as characteristic chemotaxonomic markers/targets for future metabolomic studies of Senecio/Senecioneae taxa. The MVA additionally showed that the evolution of the terpene metabolism (volatile mono- and sesquiterpenoids) within the Asteraceae tribe Senecioneae was not genera specific. However, the MVA did confirm plant-organ specific production/accumulation of volatiles within S. vernalis and suggested the existence of at least two volatile chemotypes for this species.