Comparative analysis of three Australian finger lime (Citrus australasica) cultivars: identification of unique citrus chemotypes and new volatile molecules.

The volatile constituents of the peel of three cultivars of Australian finger lime (Citrus australasica) were investigated: Alstonville, Judy's Everbearing and Durham's Emerald. Both qualitative and quantitative GC-MS analyses were performed on their peel solvent extract. The results showed that the unique phenotypes of finger lime are also correlated to unique molecular compositions. Each cultivar revealed a different chemotype: limonene/sabinene for cv. Alstonville, limonene/citronellal/isomenthone for cv. Judy's Everbearing, and limonene/citronellal/ citronellol for cv. Durham's Emerald. To the best of our knowledge, these chemotypes have never been reported in any other citrus species. Furthermore, the amounts of some volatile constituents (γ-terpinene, α-pinene, ß-pinene, citral), which are generally the major constituents besides limonene in lime species, were surprisingly low in the three cultivars. Comparative GC-MS analysis also showed that some volatile molecules tended to be specific to one cultivar and could therefore be considered as markers. Moreover six molecules were reported for the first time in a citrus extract and confirmed by synthesis. Heart-cutting enantioselective two-dimensional GC-MS was performed to determine the enantiomeric distribution of the major chiral constituents. The combined data on three finger lime cultivars gives evidence of their divergence from other citrus species.

Multidimensional gas chromatography hyphenated to mass spectrometry and olfactometry for the volatile analysis of citrus hybrid peel extract.

In this work, the volatile composition of the peel extract of limequat, a natural citrus hybrid, was investigated by using both conventional (gas chromatography-mass spectrometry [GC-MS], deconvolution) and more advanced (multidimensional GC-MS/olfactometry [MDGC-MS/O] and enantioselective [Es]-MDGC-MS/O) analytical techniques. Although the GC-MS analysis identified most of the components, some peaks remained unidentified. These unknown peaks were elucidated by deconvolution processing and using a selectable one-dimensional or two-dimensional GC-MS system equipped with an olfactometry port. The MDGC results, with both polar and chiral second dimensions, hyphenated to mass spectrometry and olfactometry, proved to be particularly useful for the identification and chiral characterization of coeluted trace compounds. In particular, the application of the Es-MDGC-MS/O configurations was used to confirm, by on-line enrichment, the presence of cis-δ-jasminlactone. This technique was fundamental for the reliable identification and exact determination of the enantiomeric distribution of this chiral compound, as well as for the sensorial evaluation of each enantiomer at the sniffing port.

Differentiation of lemon essential oil based on volatile and non-volatile fractions with various analytical techniques: a metabolomic approach.

Due to the importance of citrus lemon oil for the industry, fast and reliable analytical methods that allow the authentication and/or classification of such oil, using the origin of production or extraction process, are necessary. To evaluate the potential of volatile and non-volatile fractions for classification purposes, volatile compounds of cold-pressed lemon oils were analyzed, using GC-FID/MS and FT-MIR, while the non-volatile residues were studied, using FT-MIR, (1)H-NMR and UHPLC-TOF-MS. 64 Lemon oil samples from Argentina, Spain and Italy were considered. Unsupervised and supervised multivariate analyses were sequentially performed on various data blocks obtained by the above techniques. Successful data treatments led to statistically significant models that discriminated and classified cold-pressed lemon oils according to their geographic origin, as well as their production processes. Studying the loadings allowed highlighting of important classes of discriminant variables that corresponded to putative or identified chemical functions and compounds.

Comprehensive profiling and marker identification in non-volatile citrus oil residues by mass spectrometry and nuclear magnetic resonance.

The detailed characterization of cold-pressed lemon oils (CPLOs) is of great importance for the flavor and fragrance (F&F) industry. Since a control of authenticity by standard analytical techniques can be bypassed using elaborated adulterated oils to pretend a higher quality, a combination of advanced orthogonal methods has been developed. The present study describes a combined metabolomic approach based on UHPLC-TOF-MS profiling and (1)H NMR fingerprinting to highlight metabolite differences on a set of representative samples used in the F&F industry. A new protocol was set up and adapted to the use of CPLO residues. Multivariate analysis based on both fingerprinting methods showed significant chemical variations between Argentinian and Italian samples. Discriminating markers identified in mixtures belong to furocoumarins, flavonoids, terpenoids and fatty acids. Quantitative NMR revealed low citropten and high bergamottin content in Italian samples. The developed metabolomic approach applied to CPLO residues gives some new perspectives for authenticity assessment.