SPME applied to the study of volatile organic compounds emitted by three species of Eucalyptus in situ. Solid-phase micro extraction

Headspace solid-phase microextraction coupled to gas chromatography/ion trap mass spectrometry-65 microm polydimethylsiloxane/divinylbenzene (PDMS/DVB) was used to identify and monitor the emission patterns of biogenic volatile organic compounds from leaves of Eucalyptus dunnii, Eucalyptus saligna, and Eucalyptus citriodora in situ. Short extractions (1 min) were performed every 30 min for periods of 8-10 h during 24 days taking advantage of the high capacity of this porous polymer coating. Forty-two compounds were detected and 20 identified in the headspace of E. saligna leaves, and 19 of 27 compounds were identified in the headspace of E. dunnii leaves. The emission pattern of (E)-beta-ocimene and rose oxide suggests that they may play a bioactive role in Eucalyptus.     

Correlations between pulp properties of eucalyptus clones and leaf volatiles using automated solid-phase microextraction

Analysis of biogenic volatile organic compounds (BVOC) of 14 Eucalyptus clones has been performed using an automated headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography (GC)/ion trap mass spectrometry (ITMS) method. Correlations between pulp properties of Eucalyptus clones and the BVOC of their leaf headspaces were studied. The compounds alpha-terpineol and the sesquiterpene beta-eudesmol were positively correlated with S5, a property related to the hemicelluose content in the pulp. Qualitative results obtained with automated HS-SPME were sufficient to group together the same species and related hybrids through cluster analysis and were confirmed through principal component analysis. A preliminary separation of the essential oils of Eucalyptus dunnii through comprehensive two-dimensional gas chromatography (GC x GC) showed approximately 580 peaks compared to approximately 60 in a typical GC/ITMS first-dimension chromatogram. The potential of HS-SPME coupled to GC x GC to improve the separation of Eucalyptus volatiles and other plant essential oils looks extremely promising for new applications of unsupervised learning methods.     

Essential oil composition of sachalinmint from Norway detected by solid-phase microextraction and gas chromatography-mass spectrometry analysis

The essential oil of leaves and flowers of sachalinmint [Mentha sachalinensis (Briq.) Kud?] grown in Norway (Trondheim) has been studied by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry analysis (GC-MS). The essential oil content increased linearly in acropetal direction from 1.08% (0-20 cm plant height) to 1.75% (60-80 cm; young leaves and flowers). The steam-distilled samples showed a minor complex matrix with a very high menthol and a much lower menthone content (87.89 and 4.05%, respectively). From testing of HS-SPME unequilibrated exposure times ranging from 10 s to 5 min, an extraction time of 30 s was found to be sufficient to detect both low- and high-eluting compounds. Comparison of HS-SPME and steam-distilled samples established that the same tendencies of increasing menthol/menthone content in the basipetal/acropetal direction could be detected by both analysis methods. With regard to the extraction efficiency, HS-SPME gave additional detailed information about less important terpenic compounds.     

Chemical characterization of commercial Sherry vinegar aroma by headspace solid-phase microextraction and gas chromatography-olfactometry

The sensorial representativeness of the headspace solid-phase microextraction (HS-SPME) aroma extract from commercial Sherry vinegars has been determined by direct gas chromatography-olfactometry (D-GCO). Extracts obtained under optimal conditions were used to characterize the aroma of these vinegars by means of GCO and aroma extract dilution analysis (AEDA). Among the 37 different odorants determined, 13 of them were identified for the first time in Sherry vinegars: 2 pyrazines (3-isopropyl-2-methoxypyrazine, 3-isobutyl-2-methoxypyrazine), 2 sulfur compounds (methanethiol, dimethyl trisulfide), 1 unsaturated ketone (1-octen-3-one), 1 norisoprenoid (β-damascenone), 1 ester (ethyl trans-cinnamate) and 6 aldehydes (2- and 3-methylbutanal, octanal, nonanal, (E)-2-nonenal and (E,E)-2,4-decadienal). The determination of the odor thresholds in a hydroacetic solution together with the quantitative analysis-which was also performed using the simple and fast SPME technique-allowed obtaining the odor activity values (OAV) of the aromatic compounds found. Thus, a first pattern of their sensory importance on commercial Sherry vinegar aroma was provided.     

Volatile components of roots, stems, leaves, and flowers of Echinacea species.

The headspace volatile components of roots, stems, leaves, and flowers of Echinacea angustifolia,E. pallida, and E. purpurea were analyzed by capillary gas chromatography/mass spectrometry (GC/MS). Over 70 compounds were identified in the samples. All plant tissues, irrespective of the species, contain acetaldehyde, dimethyl sulfide, camphene, hexanal, beta-pinene, and limonene. The main headspace constituents of the aerial parts of the plant are beta-myrcene, alpha-pinene, limonene, camphene, beta-pinene, trans-ocimene, 3-hexen-1-ol, and 2-methyl-4-pentenal. The major headspace components of root tissue are alpha-phellandrene (present only in the roots of E. purpurea and E.angustifolia), dimethyl sulfide, 2-methylbutanal, 3-methylbutanal, 2-methylpropanal, acetaldehyde, camphene, 2-propanal, and limonene. Aldehydes, particularly butanals and propanals, make up 41-57% of the headspace of root tissue, 19-29% of the headspace of the leaf tissue, and only 6-14% of the headspace of flower and stem tissues. Terpenoids including alpha- and beta-pinene, beta-myrcene, ocimene, limonene, camphene, and terpinene make up 81-91% of the headspace of flowers and stems, 46-58% of the headspace of the leaf tissue, and only 6-21% of the roots. Of the 70 compounds identified, >50 are reported in Echinacea for the first time.     

Microwave-assisted headspace solid-phase microextraction for the analysis of bioemissions from Eucalyptus citriodora leaves

Microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) was developed as a simple and effective method for fast sampling of volatile organic compounds (VOCs) from Eucalyptus citriodora Hook (E. citriodora) leaves. During microwave heating, a simple shielding device made of aluminum foil was used to protect the SPME fiber from microwave irradiation while allowing the sample to be heated. A room temperature water bath was also used to allow microwave heating to be conducted in a more controlled manner. The inner heating caused by microwave irradiation dramatically accelerated the emission of VOCs from the sample, but no marked change in headspace temperature in the sample vial was found. Under optimum conditions, the extraction efficiencies obtained with microwave heating were much higher than those obtained without microwave heating for all fibers used, namely, 7-microm polydimethylsiloxane (PDMS), 100-microm polydimethylsiloxane (PDMS), 65-microm polydimethylsiloxane/divinylbenzene (PDMS/DVB), and 75-microm carboxen/polydimethylsiloxane (CAR/PDMS). The improvement of extraction efficiency using MA-HS-SPME allowed more VOC events to be detected, with more balanced extraction of VOCs of lower and higher molecular masses. Moreover, a good linear relationship was found between sample size and GC-FID response (total peak area of VOCs), indicating the usefulness of MA-HS-SPME for quantitative analysis of individual volatile compounds in E. citriodora leaves.     

Headspace solid-phase microextraction method for the study of the volatility of selected flavor compounds

Changes in the volatility of selected flavor compounds in the presence of nonvolatile food matrix components were studied using headspace solid-phase microextraction (HS-SPME) combined with GC-MS quantification. Time-dependent adsorption profiles to the SPME fiber and the partition coefficients between different phases were obtained for several individual volatiles, showing that HS-SPME analysis with a short sampling time can be used to determine the "true" headspace concentration at equilibrium between the headspace and a sample matrix. Equilibrium dialysis followed by HS-SPME/GC-MS was carried out to confirm the ability of HS-SPME extraction for monitoring the free volatile compounds in the presence of proteins. In particular, a short sampling time (1 min) avoided additional extraction of volatiles bound to the protein. Interactions between several selected flavor compounds and nonvolatile food matrix components [beta-lactoglobulin or (+)-catechin] were also studied by means of HS-SPME/GC-MS analysis. The volatility of ethyl hexanoate, heptanone, and hexanal was significantly decreased by the addition of beta-lactoglobulin compared to that of isoamyl acetate. Catechin decreased the volatility of ethyl hexanoate and hexanal by 10-20% and increased that of 2-heptanone by approximately 15%. This study indicates that HS-SPME can be a useful tool for the study of the interactions between volatile compounds and nonvolatile matrix components provided the kinetic and thermodynamic behavior of the volatiles in relation to the fiber chosen for the studies is carefully considered.     

Optimization of headspace solid-phase Microextraction (SPME) for the odor analysis of surface-ripened cheese

Fifty volatile compounds of surface smear-ripened cheese were detected and identified using headspace solid-phase microextraction (HS-SPME) and vacuum distillation coupled to gas chromatography-mass spectrometry. Changes in the headspace of aroma compounds were monitored over the whole packaging period (47 days) using the HS-SPME method. Initially, the concentration of methanethiol increased before reaching a plateau. This evolution could be linked to the growth of Brevibacterium linens. During the shelf life of cheese, levels of acetic acid and 3-methylbutanoic acid remained constant, whereas butane-2,3-dione, 3-hydroxybutan-2-one, and hydroxypropan-2-one levels gradually declined and acetone and 3-methylbutanol levels dropped sharply to a plateau. Changes in odor could be related to changes of the rind, which behaved as a barrier, strongly influencing the distribution of volatile compounds in the headspace. Using a gas chromatography-olfactometry technique without separation, it was shown that the SPME extract was representative of the cheese odor.     

Characterization of aroma compounds in apple cider using solvent-assisted flavor evaporation and headspace solid-phase microextraction

The aroma-active compounds in two apple ciders were identified using gas chromatography-olfactometry (GC-O) and GC-mass spectrometry (MS) techniques. The volatile compounds were extracted using solvent-assisted flavor evaporation (SAFE) and headspace solid-phase microextraction (HS-SPME). On the basis of odor intensity, the most important aroma compounds in the two apple cider samples were 2-phenylethanol, butanoic acid, octanoic acid, 2-methylbutanoic acid, 2-phenylethyl acetate, ethyl 2-methylbutanoate, ethyl butanoate, ethyl hexanoate, 4-ethylguaiacol, eugenol, and 4-vinylphenol. Sulfur-containing compounds, terpene derivatives, and lactones were also detected in ciders. Although most of the aroma compounds were common in both ciders, the aroma intensities were different. Comparison of extraction techniques showed that the SAFE technique had a higher recovery for acids and hydroxy-containing compounds, whereas the HS-SPME technique had a higher recovery for esters and highly volatile compounds.     

Solid-phase microextraction and gas chromatography olfactometry analysis of successively diluted samples. A new approach of the aroma extract dilution analysis applied to the characterization of wine aroma

The relationship between the composition and the aroma of the wine can be established by using gas chromatography with olfactometric detection (sniffing or GCO), which combines the chromatographic response with the human nose response. To evaluate the contribution of the odor compounds in wine aroma, we designed a new approach of the aroma extract dilution analysis (AEDA) that lies in the GCO analysis of serially diluted wine samples using headspace solid-phase microextraction (HS-SPME) as the extraction technique. The fiber coating used was Flex divinyl-carboxen-polydimethylsiloxane. The method developed was applied to determine the aromatic composition of a red Grenache wine from Priorat (Spain). The method allows 38 important odorants to be determined in the AEDA study, 30 of them precisely identified. These results are similar to those reported by other studies related to this variety of wine. HS-SPME is a suitable technique to obtain representative extracts of wine aroma with several advantages such as simplicity, speediness, and little sample manipulation.     

Improved malonaldehyde assay using headspace solid-phase microextraction and its application to the measurement of the antioxidant activity of phytochemicals

A modified malonaldehyde (MA) assay for antioxidant activity, which involves derivatization and headspace solid-phase microextraction (HS-SPME) was developed and validated. The recovery of MA as 1-methylpyrazole (product of MA and N-methylhydrazine) from a headspace of an aqueous solution containing MA, buffer, surfactant, and cod liver oil using HS-SPME with a PDMS/DVB fiber was 91.3 +/- 3.38%. MA was analyzed by a gas chromatograph with a nitrogen-phosphorus detector, and its detection limit was 0.0103 nmol/mL. The antioxidant activities of natural compounds were determined as the percentage inhibition of MA formed from cod liver oil oxidized by Fenton's reagents in the above aqueous solution. Sesamol inhibited MA formation most (86.1%), followed by eugenol (84.4%), capsaicin (80.7%), ethylvanillin (45.3%), and vanillin (31.6%) at a level of 50 microg/mL. This method did not require any organic solvents and is a simple, fast, and a highly sensitive method for MA determination.     

Quantitation of selected odor-active constituents in dry fermented sausages prepared with different curing salts

The odor-active compounds of dry-fermented sausages with added nitrite or nitrate as curing agents were identified by gas chromatography-olfactometry (GC-O) applying the detection frequency (DF) method. The quantification of these compounds in the sausage was determined by multiple headspace solid-phase microextraction (multiple HS-SPME). There were no specific odor-active compounds related to the use of nitrite or nitrate although there were differences in the DF value of several compounds. The nitrite-added sausages presented higher DF values for ethanol, 1-hexanol, propanoic acid, 2-heptenal, and nonanal while the nitrate-added sausages had higher DF values for phenylacetaldehyde and 3-methyl-butanal. Eighteen compounds were quantified by multiple HS-SPME. Most of them were above their air detection thresholds, but only hexanal, heptanal, and 1-octen-3-ol were in a concentration higher than their oil threshold values. These compounds would probably be the main contributors to the aroma of fermented sausages.     

Comparison of static headspace, headspace solid phase microextraction, headspace sorptive extraction, and direct thermal desorption techniques on chemical composition of French olive oils

Static headspace (SHS), headspace solid phase microextraction (HS-SPME), headspace sorptive extraction (HSSE), and direct thermal desorption (DTD) were applied to the analysis of four French virgin olive oils from Corsica. More than 60 compounds were isolated and characterized by GC-RI and GC-MS. SHS was not suited to the characterization of olive oil volatile compounds because of low sensitivity. The SPME and HSSE techniques were successfully applied to olive oil headspace analysis. Both methods allow the characterization of volatile compounds (mainly C(6) aldehydes and alcohols), which contribute significantly to the "green" flavor note of virgin olive oils. The PDMS stir bar showed a higher concentration capacity than a DVB/CAR/PDMS SPME fiber due to the higher volume of polymeric coating. DTD was a very good tool for extracting volatile and especially semivolatile compounds, such as sesquiterpenes, but requires a significant investment like that for HSSE. Finally, SPME may be a more appropriate technique for routine quality control due to its operational simplicity, repeatability, and low cost.     

Aroma compound analysis of Eruca sativa (Brassicaceae) SPME headspace leaf samples using GC,GC-MS,and olfactometry

The aroma compounds of rocket salad (Eruca sativa) SPME headspace samples of fresh leaves were analyzed using GC, GC-MS, and olfactometry. More than 50 constituents of the Eruca headspace could be identified to be essential volatiles, responsible for the characteristic intense green; herbal; nutty and almond-like; Brassicaceae-like (direction of cabbage, broccoli, and mustard); and horseradish-like aroma of these salad leaves. As aroma impact compounds, especially isothiocyanates, and derivatives of butane, hexane, octane, and nonane were identified. 4-Methylthiobutyl isothiocyanate (14.2%), cis-3-hexen-1-ol (11.0%), cis-3-hexenyl butanoate (10.8%), 5-methylthiopentyl isothiocyanate (9.3%), cis-3-hexenyl 2-methylbutanoate (5.4%), and 5-methylthiopentanenitrile (5.0%) were found in concentrations higher than 5.0% (calculated as % peak area of GC analysis using a nonpolar column).     

Aroma components of cooked tail meat of American lobster (Homarus americanus)

Key aroma components of cooked tail meat of American lobster (Homarus americanus) were studied by gas chromatography-olfactometry (GCO) techniques. Components of low and intermediate volatility were evaluated by aroma extract dilution analysis of solvent extracts prepared by direct solvent extraction-high vacuum distillation and vacuum steam distillation-solvent extraction, whereas headspace volatile components were assessed by GCO of decreasing headspace (static and dynamic modes) samples. Forty-seven odorants were detected by all techniques. 3-Methylbutanal (chocolate, malty), 2,3-butanedione (buttery), 3-(methylthio)propanal (cooked potato), 1-octen-3-one (mushroom), 2-acetyl-1-pyrroline (popcorn), and (E,Z)-2,6-nonadienal (cucumber), were identified as predominant odorants by all four isolation methods. The highly volatile compounds methanethiol (rotten, sulfurous) and dimethyl sulfide (canned corn) were detected by headspace methods only. These eight odorants along with three unknown compounds with crabby, amine, fishy odors were found to predominate in the overall aroma of cooked lobster tail meat.     

Characterization of volatiles and aroma-active compounds in honeybush (Cyclopia subternata) by GC-MS and GC-O analysis

Volatile organic compounds (VOCs) in fermented honeybush, Cyclopia subternata, were sampled by means of a high-capacity headspace sample enrichment probe (SEP) and analyzed by gas chromatography-mass spectrometry (GC-MS). Stereochemistry was determined by means of enantioselective GC-MS with derivatized β-cyclodextrin columns as chiral selectors. A total of 183 compounds, the majority of which are terpenoids (103; 56%), were identified by comparing their mass spectra and retention indices with those of reference compounds or tentatively identified by comparison with spectral library or literature data. Of these compounds, 37 were determined by gas chromatography-olfactometry (GC-O), using detection frequency (DF) and aroma extract dilution analysis (AEDA), to be odor-active (FD ≥ 2). (E)-β-Damascenone, (R/S)-linalool, (E)-β-damascone, geraniol, (E)-β-ionone, and (7E)-megastigma-5,7,9-trien-4-one were identified with the highest FD factors (≥512). The odors of certain compounds, that is, (6E,8Z)-megastigma-4,6,8-trien-3-one, (6E,8E)-megastigma-4,6,8-trien-3-one, (7E)-megastigma-5,7,9-trien-4-one, 10-epi-γ-eudesmol, epi-α-muurolol, and epi-α-cadinol, were perceived by GC-O assessors as typically honeybush-like.     

基于HS-SPME-GC-MS法比较瓢鸡和盐津乌骨鸡不同部位挥发性风味成分

为了研究优质地方鸡种瓢鸡和盐津乌骨鸡不同部位的主体风味成分,以300日龄瓢鸡和盐津乌骨鸡的胸肌和腿肌作为试验对象,利用顶空固相微萃取(HS-SPME)技术提取,采用气相色谱质谱联用(GC-MS)技术分离和鉴定鸡肉中的挥发性物质,结合相对活度值(ROAV)确定主体风味活性物质。结果表明,鸡肉样品中共检出76种挥发性化合物,主要包括醛类、醇类、酮类、酯类、酸类、烃类化合物,不同品种不同部位之间挥发性风味物质的组分和含量存在差异。瓢鸡主体风味物质由2-甲基丁醛、戊醛、己醛、庚醛、辛醛、反-2-辛烯醛、壬醛、1-辛烯-3-醇、辛烷构成;盐津乌骨鸡主体风味物质主要由2-甲基丁醛、己醛、壬醛、1-辛烯-3-醇构成。主体风味物质对不同部位不同品种鸡肉样品的贡献程度不同,其中醛类化合物对鸡肉的整体风味贡献最大。本研究结果为瓢鸡和盐津乌骨鸡的风味特性研究和开发利用提供了理论依据。     

Optimization of multiple headspace solid-phase microextraction for the quantification of volatile compounds in dry fermented sausages

Multiple headspace solid-phase microextraction (HS-SPME) is a stepwise method that eliminates the influence of the matrix sample on the quantitative analysis of solid samples. The process was optimized for the analysis of volatile compounds in dry fermented sausages by gas chromatography and mass spectrometry. Different amounts of fermented sausages and different vial volumes were studied to obtain the theoretical exponential decay of the peak area of the four successive extractions in order to calculate the total area in the sausage. The highest number of volatile compounds analyzed by multiple HS-SPME in dry fermented sausages was obtained in a 10 mL headspace vial with 0.07 g of sample in the presence of water, 0.75 mg butylated hydroxytoluene, and 0.5 g sodium chloride. Finally, the method was characterized in terms of linearity and detection limits and applied to analyze the volatile compounds present in fermented sausages manufactured with either nitrate or nitrite.     

Headspace solid phase microextraction applied to the analysis of organophosphorus insecticides in strawberry and cherry juices

A method based on a headspace solid phase microextraction (HS-SPME) technique followed by gas chromatography with flame thermionic and mass spectrometric detection was developed for the determination of seven organophosphorus (OPs) insecticide residues in strawberry and cherry juice samples. The extraction capacities of four fiber coatings, polyacrylate (PA 85 microm), poly(dimethylsiloxane) (PDMS 100 microm), carbowax-divinylbenzene (CW-DVB 65 microm), and poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB 65 microm), have been studied and compared. The method was developed using spiked strawberry and cherry juices in a concentration range of 0.5-50 microg/L. The PDMS 100 microm fiber showed good extraction efficiency for the target compounds. An increase in the extraction efficiency of OP insecticides was observed when the parameters affecting the HS-SPME process such as temperature, extraction time, salt additives, stirring rate, pH, and effect of dilution were optimized. Good linearity of compounds was observed in the tested concentration range. The relative standard deviations were found to be <20%. The limits of detection were between 0.025 and 0.050 microg/L. The mean relative recoveries ranged from 82 to 102%.     

Screening of tropical fruit volatile compounds using solid-phase microextraction (SPME) fibers and internally cooled SPME fiber

In this study, the optimization and comparison of an internally cooled fiber [cold fiber with polydimethylsiloxane (PDMS) loading] and several commercial solid-phase microextraction (SPME) fibers for the extraction of volatile compounds from tropical fruits were performed. Automated headspace solid-phase microextraction (HS-SPME) using commercial fibers and an internally cooled SPME fiber device coupled to gas chromatography-mass spectrometry (GC-MS) was used to identify the volatile compounds of five tropical fruits. Pulps of yellow passion fruit (Passiflora edulis), cashew (Anacardium occidentale), tamarind (Tamarindus indica L.), acerola (Malphigia glabra L.), and guava (Psidium guajava L.) were sampled. The extraction conditions were optimized using two experimental designs (full factorial design and Doehlert matrix) to analyze the main and secondary effects. The volatile compounds tentatively identified included alcohols, esters, carbonyl compounds, and terpernes. It was found that the cold fiber was the most appropriate fiber for the purpose of extracting volatile compounds from the five fruit pulps studied.