Carbon isotope ratios of selected volatiles in Citrus sinensis and in orange-flavoured food.

BACKGROUND: Twenty genuine samples of industrially cold-pressed sweet orange essential oils, were analysed by gas chromatography-combustion-isotope ratio mass spectrometry to determine the values of the carbon isotope ratios (δ(13)C(VPDB)) of selected volatiles and assess the corresponding range of authenticity. Successively, four commercial orange-flavoured products were analysed under identical conditions to evaluate the authenticity of the orange flavour. The samples were extracted by solid-phase microextraction under optimised conditions. The evaluation was performed by using an internal standard procedure to neglect the contribution due to the original environment to the isotopic abundance of (13)C. The composition of the volatile fraction of the essential oils and of the flavoured products was determined by gas chromatography coupled to mass spectrometry with linear retention indices, and by gas chromatography with a flame ionisation detector. RESULTS: The δ(13)C(VPDB) values of seven secondary metabolites determined here were successfully used to characterise genuine orange essential oil. These values were used to evaluate the quality of orange-flavoured products, revealing the presence of compounds of different origin, not compatible with the values of genuine orange secondary metabolites. CONCLUSIONS: This study provides the range of authenticity of δ(13)C(VPDB) of seven different secondary metabolites in sweet orange genuine essential oil, useful for evaluating the genuineness of orange flavour. In accord with a previous study on different essential oils, the values determined here can be successfully applied for the evaluation of a large number of flavoured food stuffs and correlated with their origins.

Sicilian lemon oil: Composition of volatile and oxygen heterocyclic fractions and enantiomeric distribution of volatile components.

A total of 92 samples of Sicilian lemon oils (Citrus limon (L.) Burm. f.) produced from September 2008 to June 2009, industrially cold-pressed by different extraction techniques (Brown Oil Extractor and Food Machinery Corporation), were analyzed by GC-flame ionization detector (FID) and GC/MS-LRI to investigate the volatile fraction; by RP-HPLC/PDA to determine the non-volatile components and by enantio-GC-FID to determine the enantiomeric ratios of 12 volatile components. This study provides a detailed investigation on the composition of Sicilian lemon essential oils industrially produced during a productive season, with the aim to recognize quality parameters for the characterization of this product. The results obtained are discussed to evaluate seasonal variation, influence of the extraction techniques, and are compared with those obtained for samples produced during different seasons.

Optimization of a comprehensive two-dimensional normal-phase and reversed-phase liquid chromatography system.

The present investigation is based on the evaluation of the performance of a comprehensive two-dimensional liquid chromatography (LCxLC) system during method optimization. The LCxLC set-up, operated in normal phase (NP) mode (adsorption) in the first dimension (1D) and reversed-phase (RP) mode in the second dimension (2D), is equipped with a 1D microbore silica column and a 2D monolithic C(18) column with a 10-port two position valve as the interface. A photodiode array detector is used after the 2D separation. A possible cause of peak distorsion because of the immiscibility of the mobile phases employed in the two dimensions is resolved. The optimization of the analytical run time and flow rate for both dimensions and the initial gradient in the 2D is carried out with various standard compounds. The potential and versatility of this LCxLC approach is demonstrated through the separation of 11 standard components, most of them allergens. The latter, which are characterized by a scattered distribution on the 2D space plane, underwent separation on both a hydrophobicity and polarity basis.

Reliability of the ΔECN42 limit and global method for extra virgin olive oil purity assessment using different analytical approaches.

Two data elaboration approaches for evaluating olive oils authenticity were compared: (I) determination of the difference between the theoretical and actual amounts of triacylglycerols with partition number 42 (ΔECN42 ⩽ |0.2|); and (II) the global method, which considers also partition numbers 44 and 46 (returning a "correct"/"not correct" result). Analysis of 31 genuine extra virgin olive oil samples was performed using different analytical methods, namely liquid chromatography (LC) coupled with a refractive index detector (RID) and LC coupled with a mass spectrometry (MS), and the results compared. Several false positives were highlighted using the ΔECN42 limit with both instrumental approaches. The global method algorithm returned "correct" results for all the samples analysed (except two that gave no results) with LC-MS; on the other hand, 10 false positives were obtained elaborating data deriving from NARP-LC-RID analysis.

Essential oil composition of Citrus meyerii Y. Tan. and Citrus medica L. cv. Diamante and their lemon hybrids.

In this paper we report the volatile fraction composition of Citrus meyerii Y. Tan. and Citrus medica L. cv. Diamante and two new lemon hybrids obtained by cross-breeding them with the tetraploid Citrus limon Burm. cv. Cavone. Both parent and hybrid oils were laboratory-extracted from the peel fruits and analyzed by HRGC-MS and HRGC-FID. Sixty-three components were fully characterized by mass spectra, linear retention indices, and injection of standards. The average composition as single components for all the oils analyzed is reported. Moreover, the data obtained were statistically analyzed. Since limonene is by far the main component of all the essential oils examined, analysis of variance and multivariate analysis gave interesting information on the similarities and differences between the oils analyzed. The new hybrid oils analyzed have potential commercial value because they could be an acceptable alternative to the valuable lemon oil.

Effects of rootstock on the composition of bergamot (Citrus bergamia Risso et Poiteau) essential oil.

This paper reports the composition of bergamot oils obtained from plants grafted on the following rootstocks: sour orange, Carrizo citrange, trifoliate orange, Alemow, Volkamerian lemon, and Troyer citrange. The aim of this study is to evaluate the possibility of using rootstocks other than sour orange, checking their effect on the composition of the essential oil. Results are reported for analysis of 203 bergamot oils during the years 1997-1998, 1998-1999, and 1999-2000. The oils were analyzed by HRGC and HRGC/MS; 78 components were identified, and the results were in agreement with those reported in the literature for the Calabrian bergamot oils obtained from industry. Because of the quality of their essential oils, Alemow and Volkamerian lemon can be considered as substitutes for sour orange rootstocks.

Evaluation of gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) for the quality assessment of citrus liqueurs.

Citrus liqueurs are alcoholic beverages obtained by maceration. The European Parliament protects these alcoholic beverages, forbidding the addition of nature-identical flavoring substances. However, for economical and technological reasons, producers often add natural and/or synthetic flavors to the alcoholic syrup, obtaining artificial spirit drinks. The aim of this study is to investigate the authenticity of Italian liqueurs, of lemon, bergamot, and mandarin (locally known as "limoncello", "bargamino", and "mandarinetto"), comparing the carbon isotope ratios with values determined in genuine cold-pressed peel oils. Authenticity assessment was performed using headspace-solid phase microextraction coupled to gas chromatography-combustion-isotope ratio mass spectrometry. Additional analyses were performed by direct enantioselective gas chromatography to determine the enantiomeric distribution of selected chiral volatiles and by gas chromatography-mass spectrometry for the qualitative analyses of the samples. The method allowed confirmation of genuineness. Enantioselective gas chromatography analyses confirmed the results, demonstrating the reliability of the method.

Gas velocity at the point of re-injection: an additional parameter in comprehensive two-dimensional gas chromatography optimization.

The present research is focused on the introduction of a new optimization parameter in the field of comprehensive 2D GC (GC×GC), herein defined as "gas velocity at the point of re-injection". GC×GC experiments were performed using a loop-type cryogenic modulator and a rapid-scanning quadrupole mass spectrometer, as detection system. All experiments were performed using a 30m×0.25mm ID apolar primary column, and a 1m×0.10mm ID medium-polarity secondary one. With regards to the modulator loops, three types of uncoated columns were used, namely with a 0.25, 0.18, and 0.10mm ID. It was found that under the same second-dimension analytical conditions (modulation, oven temperature, gas velocity) the quality of the GC×GC separation was dependent on the gas velocity at the moment of re-injection. For a loop-type modulator, the re-injection point is located at the downstream cooling/heating point of the delay loop. It was found that the GC×GC performance gradually improved when the ID of the modulator loop decreased (and the re-injection gas velocity increased), and reached its best when the 0.10mm ID uncoated column was used. GC×GC experiments were performed on a C14 n-alkane (to evaluate the efficiency of band re-injection, in terms of peak widths) and on an essential oil sample (to evaluate peak widths, resolution and the overall separation performance). The results herein reported are valid for practically any type of cryogenic modulator.

Determination of bioactive compounds in the juice of pummelo (Citrus grandis Osbeck).

The juice of pummelo (Citrus grandis Osbeck) was analyzed to determine its composition of flavonoids, polymethoxyflavones, coumarins and psoralens. The analyses were carried out by HPLC using columns packed with small diameter Fused-Core C18 particles to achieve high resolution in short analysis time. In addition, the profile of the native carotenoids present in the juice was determined using a C30 column. Identification of flavonoids was achieved by MS with ESI in negative mode; the MS acquisition of oxygenated heterocyclic compounds was performed in positive APCI; carotenoids were detected with a PDA detector. Nineteen native carotenoids were determined in pummelo juice for the first time. The composition of this juice is also discussed in comparison with other Citrus juices, especially grapefruit.

Reliable identification and quantification of volatile components of sage essential oil using ultra HRGC.

Salvia officinalis (common sage) essential oil was chemically characterized by means of GC-MS, using 100 meter capillary columns with two different stationary phases. Identification of the analytes was carried out by means of the FFNSC mass spectrum library and the use of the Linear Retention Index (LRI) as an extra criterion of library searching. Quantitative analysis was also carried out by means of GC-FID with the internal standard method and the use of relative response factors determined for each chemical class of components. A total of 45 compounds were identified and quantified and reported with their experimental LRI values.

Characterization of mandarin (Citrus deliciosa Ten.) essential oil. Determination of volatiles, non-volatiles, physico-chemical indices and enantiomeric ratios.

An investigation of 27 samples of mandarin essential oils (Citrus deliciosa Tenore), industrially produced in Sicily during the 2007-2008 season, was performed to determine the composition of the volatile fraction by GC/FID and GC/MS-LRI, the enantiomeric distribution of some monoterpene hydrocarbons and linalol by Es-GC, the non-volatile oxygen heterocyclic components by RP-HPLC/PDA and the physico-chemical indices (relative density, refractive index, optical rotation, residue on evaporation, and UV spectroscopic CD value). This study up-dates the information available in the literature on Sicilian mandarin (C. deliciosa Ten.) essential oils, and provides information on the composition and quality parameters for the evaluation of this product.

Separation of triacylglycerols in a complex lipidic matrix by using comprehensive two-dimensional liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometric detection.

The present investigation describes the employment of a comprehensive 2-D HPLC system, based on the combination of a silver ion and an RP column, for the characterization of the triacylglycerol (TAG) fraction of a very complex lipidic sample: donkey milk fat. The TAGs were grouped on the resulting bidimensional contour plot according to their double bond numbers (aligned along vertical bands) and according to their partition numbers (aligned along horizontal bands). Peak assignment was supported by using atmospheric pressure chemical ionization mass spectrometric (APCI-MS) detection. The combination of the enhanced resolving power of comprehensive multidimensional LC, the formation of ordered 2-D patterns, and APCI-MS detection proved to be an effective tool for the characterization of the complex matrix, enabling the separation and identification of nearly 60 TAGs.

Enantiomeric distribution of key volatile components in Citrus essential oils

Citrus as many other plants present characteristic distribution of some enantiomers, thus it is often possible to use this parameter for identification, characterization, genuineness, and pharmacological activity assessment. In particular, it is possible to reveal adulteration of different nature, such as addition of synthetic compounds, or natural components of different botanical origin, with drastic changes in the biological and olfactory properties. This study is focused on the evaluation of the enantiomeric excesses of numerous samples of different Citrus species: C. deliciosa Ten., C. limon (L.) Burm., C. bergamia, C. aurantifolia (Christm.) Swing., C. latifolia Tan., C. sinensis (L.) Osbeck, and C. aurantium L. The enantiomeric distribution is determined by direct esGC and, depending on the complexity of the essential oil, by MDGC with a chiral column in the second dimension. The research is focused on the determination of fourteen chiral components which present specific distribution in the essential oils investigated. Particular attention is given to the trend of the enantiomeric distribution during the productive season, so to identify useful parameters for quality assessment also in consideration of the wide range of variability often reported in literature. The components investigated were the following: α-thujene, α-pinene, camphene, β-pinene, sabinene, α-phellandrene, β-phellandrene, limonene, linalool, camphor, citronellal, linalyl acetate, terpinen-4-ol, α-terpineol. The use of MDGC allowed the separation of the enantiomers of camphor and citronellal, otherwise not separated by conventional esGC; however for the separation of the enantiomers of α-pinene it was preferable to use conventional esGC. The MDGC system allowed to determine the enantiomeric distribution of camphene, α- and β-phellandrene in lime essential oil for the first time. The results are discussed in function of seasonal variation and, when possible, in function of the extraction technology, with particular regards to lime oils.

Determination of triacylglycerols in donkey milk by using high performance liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry.

The separation and determination of triacylglycerols (TAGs), which are the main components of naturally occurring fats and oils, in milk fat is a challenging task due to the very complex nature of this matrix. In the present study the TAG fraction of donkey milk lipids has been characterized by using high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS). HPLC in reversed phase mode has been used for TAG separation and silver ion (Ag+) HPLC has been used as a second dimension to clarify and confirm the identification. The RP-HPLC eluate was fractionated and the fractions of interest were injected onto the Ag+-HPLC column. In both cases peak assignment was carried out by combining retention data with APCI-MS spectra information. In total, 55 TAGs in donkey milk fat were identified (without considering the positional isomers) and quantified on the basis of percentage peak areas in the RP-HPLC chromatogram (without the use of correction factors). Amongst the identified triacylglycerols, POLn, POO, PPO, CaPO, POL, and PPoO proved to be the main components of the TAG fraction of donkey milk.