The volatile fraction of natural products often consists of complex mixtures of isomeric and/or homologous components with similar structural and physical characteristics (e.g. mono- and ...sesquiterpenoids) that are not easy to separate simultaneously with conventional GC stationary phases, even when used with multidimensional systems. The introduction of ionic liquids (ILs) as stationary phases has opened up new perspectives in this field as their unique solvation properties result in uncommon selectivity, which is completely different to that of classic polydimethylsiloxane (PDMS)- and polyethyleneglycol (PEG)-based columns. Because of their peculiar selectivity and high inertness, IL-based columns have already found several applications in the natural product field in mono- and multidimensional GC and preparative GC, leading to the exhaustive analysis of complex samples (including aqueous solutions), and the separation of challenging pair(s) of compounds. This article provides an overview of how IL-based columns can be exploited in the fields of food and natural products, explores the wide range of applications that have already been developed and highlights the main features of these promising stationary phases, which are expected to be further extended in the near future, in particular, for routine use.
Graphical abstract
Modern omics disciplines dealing with food flavor focus the analytical efforts on the elucidation of sensory-active compounds, including all possible stimuli of multimodal perception (aroma, taste, ...texture, etc.) by means of a comprehensive, integrated treatment of sample constituents, such as physicochemical properties, concentration in the matrix, and sensory properties (odor/taste quality, perception threshold). Such analyses require detailed profiling of known bioactive components as well as advanced fingerprinting techniques to catalog sample constituents comprehensively, quantitatively, and comparably across samples. Multidimensional analytical platforms support comprehensive investigations required for flavor analysis by combining information on analytes’ identities, physicochemical behaviors (volatility, polarity, partition coefficient, and solubility), concentration, and odor quality. Unlike other omics, flavor metabolomics and sensomics include the final output of the biological phenomenon (i.e., sensory perceptions) as an additional analytical dimension, which is specifically and exclusively triggered by the chemicals analyzed. However, advanced omics platforms, which are multidimensional by definition, pose challenging issues not only in terms of coupling with detection systems and sample preparation, but also in terms of data elaboration and processing. The large number of variables collected during each analytical run provides a high level of information, but requires appropriate strategies to exploit fully this potential. This review focuses on advances in comprehensive two-dimensional gas chromatography and analytical platforms combining two-dimensional gas chromatography with olfactometry, chemometrics, and quantitative assays for food sensory analysis to assess the quality of a given product. We review instrumental advances and couplings, automation in sample preparation, data elaboration, and a selection of applications.
Graphical Abstract
GC×GC Food Sensory
The quality control of essential oils (EO) principally aims at revealing the presence of adulterations and at quantifying compounds that are limited by law by evaluating EO chemical compositions, ...usually in terms of the normalised relative abundance of selected markers, for comparison to reference values reported in pharmacopoeias and/or international norms. Common adulterations of EO consist of the addition of cheaper EO or synthetic materials. This adulteration can be detected by calculating the percent normalised areas of selected markers or the enantiomeric composition of chiral components. The dilution of the EO with vegetable oils is another type of adulteration. This adulteration is quite devious, as it modifies neither the qualitative composition of the resulting EO nor the marker's normalised percentage abundance, which is no longer diagnostic, and an absolute quantitative analysis is required. This study aims at verifying the application of the two above approaches (i.e., normalised relative abundance and absolute quantitation) to detect EO adulterations, with examples involving selected commercial EO (lavender, bergamot and tea tree) adulterated with synthetic components, EO of different origin and lower economical values and heavy vegetable oils. The results show that absolute quantitation is necessary to highlight adulteration with heavy vegetable oils, providing that a reference quantitative profile is available.
This study applied an untargeted-targeted (UT) fingerprinting approach, based on comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOF MS), to assess the ...effects of rainfall and temperature (both seasonal and elevational) on the tea metabolome. By this strategy, the same compound found in multiple samples need only to be identified once, since chromatograms and mass spectral features are aligned in the data analysis process. Primary and specialized metabolites of leaves from two Chinese provinces, Yunnan (pu'erh) and Fujian (oolong), and a farm in South Carolina (USA, black tea) were studied. UT fingerprinting provided insight into plant metabolism activation/inhibition, taste and trigeminal sensations, and antioxidant properties, not easily attained by other analytical approaches. For example, pu'erh and oolong contained higher relative amounts of amino acids, organic acids, and sugars. Conversely, black tea contained less of all targeted compounds except fructose and glucose, which were more similar to oolong tea. Findings revealed compounds statistically different between spring (pre-monsoon) and summer (monsoon) in pu'erh and oolong teas as well as compounds that exhibited the greatest variability due to seasonal and elevational differences. The UT fingerprinting approach offered unique insights into how differences in growing conditions and commercial processing affect the nutritional benefits and sensory characteristics of tea beverages.
Tea infusions are the most consumed beverages in the world after water; their pleasant yet peculiar flavor profile drives consumer choice and acceptance and becomes a fundamental benchmark for the ...industry. Any qualification method capable of objectifying the product's sensory features effectively supports industrial quality control laboratories in guaranteeing high sample throughputs even without human panel intervention. The current study presents an integrated analytical strategy acting as an Artificial Intelligence decision tool for black tea infusion aroma and taste blueprinting. Key markers validated by sensomics are accurately quantified in a wide dynamic range of concentrations. Thirteen key aromas are quantitatively assessed by standard addition with in-solution solid-phase microextraction sampling followed by GC-MS. On the other hand, nineteen key taste and quality markers are quantified by external standard calibration and LC-UV/DAD. The large dynamic range of concentration for sensory markers is reflected in the selection of seven high-quality teas from different geographical areas (Ceylon, Darjeeling Testa Valley and Castleton, Assam, Yunnan, Azores, and Kenya). The strategy as a sensomics-based expert system predicts teas' sensory features and acts as an AI smelling and taste machine suitable for quality controls.
•Chemical structures of 9 PIL SPME coatings are examined for acrylamide selectivity.•Coatings containing hydroxyl functional groups exhibited lowest LODs for acrylamide.•In-solution SPME sampling was ...applied in brewed coffee and coffee powder.•The best PIL fiber produced a limit of quantitation for acrylamide of 0.5μgL−1.•All coatings were imaged by SEM and were observed to be matrix-compatible.
Nine crosslinked polymeric ionic liquid (PIL)-based SPME sorbent coatings were designed and screened in this study for the trace level determination of acrylamide in brewed coffee and coffee powder using gas chromatography–mass spectrometry (GC–MS). The structure of the ionic liquid (IL) monomer was tailored by introducing different functional groups to the cation and the nature of the IL crosslinker was designed by altering both the structure of the cation as well as counteranions. The extraction efficiency of the new PIL coatings towards acrylamide was investigated and compared to a previously reported PIL sorbent coating. All PIL fibers exhibited excellent analytical precision and linearity. The PIL fiber coating consisting of 50% 1,12-di(3-vinylbenzylbenzimidazolium)dodecane dibis(trifluoromethyl)sulfonylimide as IL crosslinker in 1-vinyl-3-(10-hydroxydecyl)imidazolium bis(trifluoromethyl)sulfonylimide IL monomer resulted in a limit of quantitation of 0.5μgL−1 with in-solution SPME sampling. The hydroxyl moiety appended to the IL cation was observed to significantly increase the sensitivity of the PIL coating toward acrylamide. The quantitation of acrylamide in brewed coffee and coffee powder was performed using the different PIL-based fibers by the method of standard addition after a quenching reaction using ninhydrin to inhibit the formation of interfering acrylamide in the GC inlet, mainly by asparagine thermal degradation. Excellent repeatability with relative standard deviations below 10% were obtained on the real coffee samples and the structure of the coatings appeared intact by scanning electron microscopy after coffee sampling proving the matrix-compatibility of the PIL sorbent coatings.
A novel chemical profile essential oil, distilled from the aerial parts of
(Kunth) Govaerts (Lamiaceae), was analysed by Gas Chromatography-Mass Spectrometry (GC-MS, qualitative analysis) and Gas ...Chromatography with Flame Ionization Detector (GC-FID, quantitative analysis), with both polar and non-polar stationary phase columns. The chemical composition mostly consisted of sesquiterpenes and sesquiterpenoids (>70%), the main ones being (
)-
-caryophyllene (17.8%),
-copaene (10.5%),
-bourbonene (9.9%),
-cadinene (6.6%),
-cadina-1(6),4-diene (6.4%) and germacrene D (4.9%), with the non-polar column. The essential oil was then submitted to enantioselective GC analysis, with a diethyl-
-butyldimethylsilyl-
-cyclodextrin diluted in PS-086 chiral selector, resulting in the following enantiomeric excesses for the chiral components: (1
,5
)-(-)-
-thujene (67.8%), (1
,5
)-(+)-
-pinene (85.5%), (1
,5
)-(-)-
-pinene (90.0%), (1
,5
)-(-)-sabinene (12.3%), (
)-(-)-limonene (88.1%), (
)-(+)-linalool (32.7%), (
)-(-)-terpinen-4-ol (9.3%), (
)-(-)-
-terpineol (71.2%) and (
)-(-)-germacrene D (89.0%). The inhibition activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) of
essential oil was then tested, resulting in selective activity against BChE with an IC
value of 31.3 ± 3.0 μg/mL (positive control: donepezil, IC
= 3.6 μg/mL).
The evolution of vapour phase sampling of the volatile fraction of vegetable matrices, or of products directly related to them, over the period 1996–2007 is reviewed. High concentration capacity ...headspace (HCC-HS) and dynamic headspace (D-HS) techniques, that is headspace sampling approaches where the analytes in the vapour phase are concentrated into a sorbent, an adsorbent or a solvent, are considered. Advantages, disadvantages and applications to the vegetable field of several successful techniques based on these approaches are critically presented, including in-tube sorptive extraction (INCAT, HS-SPDE), headspace sorptive extraction (HSSE), solid-phase aroma concentrate extraction (SPACE), large surface area HCC-HS sampling (MESI, MME, HS-STE), headspace liquid-phase microextraction (HS-LPME) and dynamic headspace samplings (D-HS). The developments necessary to overcome some of the limits of the above approaches and techniques are also discussed in view of their application to new fields.
The volatilome of hazelnuts (
L.) encrypts information about phenotype expression as a function of cultivar/origin, post-harvest practices, and their impact on primary metabolome, storage conditions ...and shelf-life, spoilage, and quality deterioration. Moreover, within the bulk of detectable volatiles, just a few of them play a key role in defining distinctive aroma (i.e., aroma blueprint) and conferring characteristic hedonic profile. In particular, in raw hazelnuts, key-odorants as defined by
are: 2,3-diethyl-5-methylpyrazine (
and
); 2-acetyl-1,4,5,6-tetrahydropyridine (
); 2-acetyl-1-pyrroline (
); 2-acetyl-3,4,5,6-tetrahydropyridine (
); 3-(methylthio)-propanal (
); 3-(methylthio)propionaldehyde (
); 3,7-dimethylocta-1,6-dien-3-ol/linalool (citrus, floral); 3-methyl-4-heptanone (
); and 5-methyl-(E)-2-hepten-4-one (
). Dry-roasting on hazelnut kernels triggers the formation of additional potent odorants, likely contributing to the pleasant aroma of roasted nuts. Whiting the newly formed aromas, 2,3-pentanedione (
); 2-propionyl-1-pyrroline (
); 3-methylbutanal; (
); 4-hydroxy-2,5-dimethyl-3(2H)-furanone (
); dimethyl trisulfide (
) are worthy to be mentioned. The review focuses on high-quality hazelnuts adopted as premium primary material by the confectionery industry. Information on primary and secondary/specialized metabolites distribution introduces more specialized sections focused on volatilome chemical dimensions and their correlation to cultivar/origin, post-harvest practices and storage, and spoilage phenomena. Sensory-driven studies, based on
principles, provide insights on the aroma blueprint of raw and roasted hazelnuts while robust correlations between non-volatile precursors and key-aroma compounds pose solid foundations to the conceptualization of
.
Identifying all analytes in a natural product is a daunting challenge, even if fractionated by volatility. In this study, comprehensive two-dimensional gas chromatography/mass spectrometry (GC×GC-MS) ...was used to investigate relative distribution of volatiles in green, pu-erh tea from leaves collected at two different elevations (1162 m and 1651 m). A total of 317 high and 280 low elevation compounds were detected, many of them known to have sensory and health beneficial properties. The samples were evaluated by two different software. The first, GC Image, used feature-based detection algorithms to identify spectral patterns and peak-regions, leading to tentative identification of 107 compounds. The software produced a composite map illustrating differences in the samples. The second, Ion Analytics, employed spectral deconvolution algorithms to detect target compounds, then subtracted their spectra from the total ion current chromatogram to reveal untargeted compounds. Compound identities were more easily assigned, since chromatogram complexities were reduced. Of the 317 compounds, for example, 34% were positively identified and 42% were tentatively identified, leaving 24% as unknowns. This study demonstrated the targeted/untargeted approach taken simplifies the analysis time for large data sets, leading to a better understanding of the chemistry behind biological phenomena.
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