Characterisation of volatile compounds in Tunisian fenugreek seeds

In this study, we intend to develop a simple and fast analytical procedure to identify the volatile compounds implicated in the odour of Tunisian fenugreek (Trigonella foenum-graceum L.) seeds. Two procedures, solvent extraction and static headspace solid-phase microextraction (SHS-SPME), have been used under different conditions. The volatile compounds extracted were systematically identified using gas chromatography–mass spectrometry, based on their mass spectrum and Kovats index on two columns of different polarity. A total of 67 compounds were identified, some of them being reported for the first time in fenugreek seeds (e.g. several pyrazines, 2,5-dimethyl-4-hydroxy-3(2H)-furanone or 1-epi-cubenol). Methanol was found to be the preferred solvent for high and medium boiling point volatile compounds, such as sotolone and nitrogen compounds. For SHS-SPME, the fibre coated with divinylbenzene/carboxen/polydimethylsiloxane 2 cm was the most suitable for extracting volatile compounds from ground seeds. The efficiency of this fibre was confirmed by direct gas chromatography–olfactometry, with a global odour similar to that of fenugreek seeds.     

Influence of the type of fiber coating and extraction time on foal dry-cured loin volatile compounds extracted by solid-phase microextraction (SPME)

Extraction of dry-cured loin volatile compounds by solid-phase microextraction (SPME) was optimized. Two different fiber coatings: carboxen/polydimethylsiloxane (CAR/PDMS) and divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS), and three extraction times (15, 30 and 45 min) were assayed. Between the fibers tested, CAR/PDMS coated fibers extracted between two and three times more total amount of volatile compounds than the DVD/CAR/PDMS coating (1314 × 10⁶ vs. 526 × 10⁶ area units). Fifty five compounds were extracted by the CAR/PDMS fiber, while only 48 of these were found with the DVB/CAR/PDMS fiber. On the other hand, 6 additional volatile compounds were extracted by the CAR/PDMS coating, all of them being of low molecular weight. Three of the major compounds extracted, hexanoic acid, methyl ester; butanoic acid, 3-methyl-, methyl ester and hexanal, were found in high proportion in both fiber coatings. The effect of exposure time was more marked for the DVD/CAR/PDMS fiber than for the CAR/PDMS coating. Fifteen minutes of extraction provided a volatile compounds profile with lower area counts for most compounds and significantly different to that obtained with 30 and 45 min of extraction. The extraction yields of dry-cured loin volatile compounds varied according to the fiber coating used and the time of exposure. Therefore, extraction conditions should be selected depending on the objective of the study. Finally, it can be concluded that both porous fibers tested, CAR/PDMS and DVB/CAR/PDMS, provide a similar volatile compounds profile for dry-cured foal loin.     

A headspace solid-phase microextraction method development and its application in the determination of volatiles in honeys by gas chromatography

The first part of the paper presents the detailed optimisation of all steps of the determination procedure of volatiles from Polish honeys by headspace solid-phase microextraction (HS-SPME) as the sample preparation method and gas chromatography/mass spectrometry (GC–MS) as the method of final determination. In the result, the following conditions were applied: CAR/PDMS/DVB SPME fibre, the sample composition (5:1 w/w honey to water ratio), 3 g sample size. The other procedure parameters, like the temperatures of individual stages of the process, were also included.     

Influence of free fatty acids, sterols and phospholipids on volatile compounds in olive oil headspace determined by solid phase microextraction-gas chromatography

In order to study the influence of some polar compounds, naturally present in virgin olive oils (VOOs), on the volatiles release, the volatiles-free olive oil matrix was enriched with free fatty acids (FFA) (concentration range from 0.35 to 1.40 g/100 g), sterols (1.0–2.5 g/kg) and phospholipids (1.6–6.0 g/kg). Sixteen standards of VOO aroma compounds were dissolved in thus obtained olive oil matrices. Volatile compounds were analysed by headspace solid phase microextraction with DVB/CAR/PDMS fibre and gas chromatography with flame ionization detection. Evaluation of the data by statistical analysis revealed that FFA, sterols and phospholipids, in concentration ranges considered in this study, generally did not significantly influence the determination of VOO volatiles. The most important changes occurred in the release of the three alcohols (Z-2-penten-1-ol, 1-hexanol and E-3-hexen-1-ol) and 3-methylbutyl acetate which slightly decreased upon the increase of FFA concentration.     

Solid-phase microextraction for headspace analysis of key volatile compounds in orange beverage emulsion

Headspace solid-phase microextraction (HS-SPME) gas chromatography was used to analyze target flavor compounds in orange beverage emulsion. The effects of SPME fiber (PDMS 100 μm, CAR/PDMS 75 μm, PDMS/DVB 65 μm and DVB/CAR/PDMS 50/30 μm), adsorption temperature (25–45 °C), adsorption time (5–25 min), sample concentration (1–100%), sample amount (5–12.5 g), pH (2.5–9.5), salt type (K₂CO₃, Na₂CO₃, NaCl and Na₂SO₄), salt amounts (0–30%) and stirring mode were studied to develop HS-SPME condition for obtaining the highest extraction efficiency and aroma recovery. For the head space volatile extraction, the optimum conditions were: CAR/PDMS fiber, adsorption at 45 °C for 15 min, 5 g of diluted beverage emulsion (1:100), 15% (w/w) of NaCl with stirring and original pH 4. The main volatile flavor compounds were: limonene, 94.9%; myrcene, 1.2%; ethyl butyrate, 1.1%; γ-terpinene, 0.41%; linalool, 0.36%; 3-carene, 0.16%; decanal, 0.12%; ethyl acetate, 0.1%; 1-octanol, 0.06%; geranial, 0.05%; β-pinene, 0.04%; octanal, 0.03%; α-pinene, 0.03%; and neral, 0.03%. The linearity was very good in the considered concentration ranges (R² ? 0.97). Average recoveries ranged from 88.3% to 121.7% and showed good accuracy for the proposed analytical method. Average relative standard deviation (RSD) for five replicate analyses was found to be less than 14%. The limit of detection (LOD) ranged from 0.06 to 2.27 mg/l for all volatile flavor compounds and confirmed the feasibility of the HS-SPME technique for headspace analysis of orange beverage emulsion. The method was successfully applied for headspace analysis of five commercial orange beverage emulsions.     

Analysis of volatile compounds in traditional smoke-cured bacon(CSCB) with different fiber coatings using SPME

The volatile compounds of Chinese traditional smoke-cured bacon (CSCB) were studied using SPMS-GC/MS. There were 48 volatile compounds identified and quantified, which belonged to several classes of chemical: 1 alkane, 16 aldehydes, 5 ketones, 9 alcohols, 4 thioethers and thiols, 3 furans and 10 phenols compounds. All the volatile compounds except for alkane was responsible for CSCB characteristic flavor. The major volatile compounds of CSCB came from smoking, oxidation and Maillard reaction, etc. Many volatile compounds were not reported in previous paper isolated by steam distillation method or nitrogen purge-and-steam distillation method on CSCB. It should be because of different method of isolating volatile substances from CSCB. Among the fibers tested, CAR/PDMS (carboxen/polydimethylsiloxane) fiber coating showed the highest area counts for most volatile compounds. CAR/PDMS coating extracted better those compounds whose linear retention indices (LRI) was lower than 926 (on average) and DVB/CAR/PDMS (divinylbenzene/carboxen/polydimethylsiloxane) those with higher LRI.     

Differentiation of “Claret”, Rosé, Red and Blend wines based on the content of volatile compounds by headspace solid-phase microextraction and gas chromatography

We studied 46 samples of wine from Denomination of Origin of La Rioja: 8 rosé, 8 “claret”, 10 red, 10 artificial blend and 10 ungrouped wines (3 rosé, 2 “claret”, 2 red and 3 blend). The samples were analysed by gas chromatography using headspace-solid-phase microextraction (HS-SPME) with a Carbowax-divinylbenzene (CW/DVB) fibre. The variables considered were 3-methyl butyl acetate, 3-methyl-1-butanol, ethyl hexanoate, 1-hexanol, ethyl octanoate, diethyl succinate, hexanoic acid, 2-phenylethanol, octanoic acid, decanoic acid and geraniol, all significant for distinguishing the types of wines except 3 metil-1-butanol and 1-hexanol. The different wine samples were classified by multivariate statistical methods. Good differentiation between the different groups of samples was achieved by means of principal component analysis and hierarchical cluster analysis. Linear discriminant analysis was used to differentiate and classify these wines. 3-methyl-butyl acetate, ethyl octanoate, diethyl succinate, hexanoic acid, 2-phenylethanol and decanoic acid were the most discriminant variables and gave 100% recognition ability and 100% prediction ability.     

Analysis of volatile compounds of pineapple wine using solid-phase microextraction techniques

An analytical procedure based on headspace solid-phase microextraction (HS-SPME) method combined with GC–MS was developed for the extraction and quantification of volatile compounds from pineapple wine. Different sample preparation (SPME fibre type, addition of sodium chloride, extraction time and temperature) were evaluated to optimise the method. For the final method, 8 ml of pineapple wine were placed in a 15 ml headspace vial with addition of 1 g of NaCl; a polydimethylsiloxane SPME fibre was used for extraction at 30 °C for 30 min with continuous stirring. The volatile compounds have shown a good linearity in the range of concentrations studied with regression coefficients higher than 0.98, and the reproducibility expressed as relative standard deviation ranged from 4.2% (2-phenylethyl acetate) to 7.1% (ethyl benzoate). The values obtained for detection and quantification limits were low enough to permit the determination of volatiles in pineapple wine. Using this method, 18 volatiles were identified, including 13 esters, 4 alcohols and one acid. Ethyl octanoate, ethyl acetate, 3-methyl-1-butanol and ethyl decanoate were the major constituents. A tentative study to estimate the contribution of the identified compounds to the aroma of the wine, on the basis of their odour activity values (OAV), indicated that the compounds potentially most important to pineapple wine included ethyl octanoate, ethyl acetate and ethyl 2-methylpropanoate.     

Analysis of volatile compounds of eucalyptus honey by solid phase extraction followed by gas chromatography coupled to mass spectrometry

Solid-phase extraction (SPE) followed by gas chromatography coupled to mass spectrometry has been used for the analysis of volatile compounds of eucalyptus honey. Different amounts of honey and dichloromethane were employed to optimize solid-phase extraction conditions. The best result was obtained with 20 g of honey eluted with 60 mL of dichloromethane. This method presented a good precision for volatile compounds usually found in honeys and allowed the quantification of 35 volatile compounds (terpenes and derivatives, furan and pyran compounds, ketones, benzene compounds, acids, and norisoprenoids) of eucalyptus honey.     

Application of solid-phase microextraction to the analysis of volatile compounds in virgin olive oils from five new cultivars

Evaluation and identification of wild olive genetic resources allowed us to select new olive varieties and to recognize Tunisian grove richness and diversity. Five new olive cultivars were previously selected among populations of wild olive plants on the basis of agronomic and chemical evaluations. Their virgin olive oils were analysed for their fatty acid composition, quality indices (Free acidity, PV and UV characteristics) and oxidative stability. They were then submitted to solid phase microextraction (SPME) and their volatile compositions were determined.     

Characterization of volatile compounds in fermented milk using solid-phase microextraction methods coupled with gas chromatography-mass spectrometry

Lactic acid bacteria (LAB) are industrially important bacteria that are widely used in the fermented food industry, especially in the manufacture of yogurt. Characteristic flavors are produced by LAB during fermentation and storage that affect the quality and acceptability of fermented milk products. In this study, the volatile compounds in milk fermented by Streptococcus thermophilus IMAU80842 alone, Lactobacillus delbrueckii ssp. bulgaricus IMAU20401 alone, or both species together were identified using solid-phase microextraction methods coupled with gas chromatography-mass spectrometry. A total of 53, 43, and 32 volatile compounds were identified in milk fermented by S. thermophilus alone, L. delbrueckii ssp. bulgaricus alone, or both species together, respectively. The presence of some important flavor compounds was confirmed: acetic acid, acetaldehyde, acetoin, 2,3-butanedione, ethanol, and 1-heptanol. Our results demonstrate that the composition of the volatile compounds in fermented milk depends on the species of LAB used and whether they are used alone or in combination. This is important for the selection of appropriate starter cultures for the production of different types of fermented milk product with particular flavors.     

Analysis of human male armpit sweat after fenugreek ingestion: Characterisation of odour active compounds by gas chromatography coupled to mass spectrometry and olfactometry

In this study, the strong “maple-syrup” odour which appears after fenugreek ingestion was investigated. Headspace solid-phase microextraction (HS-SPME) was applied to extract volatile odourant compounds from human male armpit sweat samples. Two male volunteers were considered who have similar diet; they had to ingest fenugreek infusion over the same period of time. The HS-SPME extracts obtained were then analysed by gas chromatography coupled either to mass spectrometry (GC–MS) or flame ionisation detection and olfactometry (GC–O). In that latter case, a panel of eight assessors was used, and the detection frequency methodology was applied. A total of 44 compounds could be identified in sweat samples, with a wide range of chemical structures, some of them being reported for the first time in human armpit sweat. Eight compounds appearing only after fenugreek ingestion could be identified: 2,5-dimethylpyrazine, β-pinene, 3-octen-2-one, camphor, terpinen-4-ol, 4-isopropyl-benzaldehyde, neryl acetate and β-caryophyllene. Due to their odourant notes, such compounds should be responsible for the strong “maple-syrup” odour present in sweat after fenugreek ingestion. GC–O confirmed the role of some odourant compounds in the “maple-syrup” odour of sweat, especially 2,5-dimethylpyrazine which was the best perceived odour. Among these eight compounds, some of them were previously reported in the fenugreek seeds, namely β-pinene, 3-octen-2-one and camphor.     

Discrimination of Chinese vinegars based on headspace solid-phase microextraction-gas chromatography mass spectrometry of volatile compounds and multivariate analysis

Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography mass spectrometry (GC-MS) was applied for the determination of the characteristic volatile profiles of Chinese vinegars. Multivariate statistical techniques, such as principal component analysis (PCA) and cluster analysis (CA), were used to characterize the different Chinese vinegars by types, fermentation method, and production area. A total of 56 volatile compounds were identified, including 15 esters, 10 aldehydes, 5 acids, 12 alcohols, 5 ketones, 4 volatile phenols, 2 pyrazines, and 3 miscellaneous compounds. The major compounds in Chinese vinegars were furfural, acetic acid, ethyl acetate, 3-hydroxy-2-butanone, 3-methyl-1-butanol, isopentyl acetate, benzaldehyde, phenylethyl alcohol. The PCA results showed that characterizing the Chinese vinegars by HS-SPME-GC-MS was highly related to their type, fermentation method, and production area, and all these influencing factors were not independent. The CA results indicated that the fermentation method had a greater effect than vinegar type and production area. The results showed that HS-SPME-GC-MS together with chemometrics could provide practical reference for characterization of Chinese vinegars. Practical Application: HS-SPME coupled with GC-MS was applied for the determination of the characteristic volatile profiles of Chinese vinegars. The major compounds in Chinese vinegars were furfural, acetic acid, ethyl acetate, 3-hydroxy-2-butanone, 3-methyl-1-butanol, isopentyl acetate, benzaldehyde, phenylethyl alcohol. HS-SPME-GC-MS together with chemometrics was an efficient tool for evaluating vinegar authenticity.     

气相色谱法分析卷烟烟气中的醛类化合物

本文研究了采用毛细管气相色谱仪分析卷烟烟气中醛类化合物的方法。在标准条件下吸烟,使卷烟烟气通过装有2,4-二硝基苯肼(DNPH)衍生化试剂酸性溶液的捕集装置,烟气中的醛类化合物与DNPH反应,生成稳定的2,4-二硝基苯腙衍生物,经三氯甲烷萃取,并在氮气保护下浓缩后,采用配备氮-磷检测器(NPD)的毛细管气相色谱仪进行分析。本文评价了该方法测定卷烟烟气中甲醛、乙醛和丙烯醛的重复性及回收率,并采用内标法定量测定了9种牌号卷烟烟气中的甲醛、乙醛和丙烯醛的输送量以及卷烟滤嘴对甲醛的截滤效率。采用气/联用仪(GC/S)和标样加入法鉴定出卷烟烟气中的12种醛类化合物。该方法操作简便,重复性好,回收率高,适用于卷烟烟气中醛类化合物的分析。      

Yeast derivatives (extracts and autolysates) in winemaking: Release of volatile compounds and effects on wine aroma volatility

A qualitative study of volatile compounds in three commercial yeast extracts and autolysates was performed by solid-phase microextraction-gas chromatography with mass spectrometric and olfactometric detection; their addition to white wines and their effect on wine aroma composition were investigated by analytical, olfactometric and sensory evaluations. More than 160 volatile compounds were detected in the headspace of the commercial powders (some not previously reported in literature), and their olfactory characters were described. Yeast derivatives strongly modified wine aroma composition, either affecting the volatility of wine aroma compounds or by releasing exogenous volatiles. Dosage appeared to be fundamental: low amounts increased the volatility of some esters, giving more flowery and fruity notes to the wine; higher amounts increased fatty acid content in the wine headspace, producing yeasty, herbaceous and cheese-like smells. Sensory tests demonstrated that yeast derivatives would not be suitable for wines with a typical varietal aroma.     

Behaviour of volatile compounds during the shelf life of yoghurt

The production of acetaldehyde, diacetyl and ethanol was evaluated in whole plain yoghurts manufactured with commercial starter cultures, yoghurt acquired in a local market, and milk fermented by a single culture of either Streptococcus thermophilus or Lactobacillus delbrueckii ssp. bulgaricus . The headspace technique was used for sample preparation, following identification and quantification by gas chromatography. During an 8-h incubation period, mixed cultures were the most efficient in lowering the pH (from 6.30 to 4.8), followed by S. thermophilus (from 6.30 to 5.18) and L. bulgaricus (from 6.30 to 5.8). During the storage period, however, a single culture of L. bulgaricus decreased the pH more than S. thermophilus , but still less than the mixed commercial cultures. Plain yoghurts acquired in the market, those made with commercial starter cultures, and fermented milks obtained with single cultures showed, after 21 days of storage, concentrations of acetaldehyde from 11 to 35 mg/L, and of diacetyl from 0 to 0.85 mg/L. An increasing concentration of ethanol was observed during the storage period, and its production was observed even in the incubation stage of all products. It was also observed that the acetaldehyde concentration was inversely correlated to ethanol production in some products. The combination of headspace, identification and quantification techniques by gas chromatography in this work was efficient in the identification and quantification of the major aromatic compounds and ethanol content of yoghurt.     

SPME/GC-MS characterization of volatile compounds of Iranian traditional dried Kashk

The volatile aromatic components in cow’s or sheep’s milk Kashk samples collected from 11 regions of Iran were extracted by solid-phase micro-extraction and analyzed by GC/MS. Alkenes, aldehydes, free fatty acids, esters, terpenes, alcohols, sulfur compounds, and ketones were the most frequently used compounds in samples. Same volatile compounds were identified in sheep’s and cows’ milk Kashk, whereas the numbers of compounds were different. The results from principle component analysis (PCA), performed to distinguish flavor from different regions, showed that Kashk samples are divided into three groups, in which flavor of some regions in two groups is affected by ingredients.     

Analysis of volatile compounds in edible oils using simultaneous distillation-solvent extraction and direct coupling of liquid chromatography with gas chromatography

 Identification of volatile compounds in different edible oils (i.e. olive oil, almond oil, hazelnut oil, peanut oil and walnut oil) was performed using simultaneous distillation-solvent extraction followed by gas chromatographic-mass spectrometric analysis. An alternative approach which allows the direct injection of the oil sample (i.e. without any kind of pre-treatment) and involves the use of on-line coupled reversed phase liquid chromatography-gas chromatography (RPLC-GC) was also considered and the advantages of avoiding off-line preseparation for the analysis of volatile compounds were underlined regarding difficulties associated with the lipophilic nature of most volatile compounds and, hence, with the reliability of their analysis. Received: 14 June 1999 / Revised version: 3 August 1999     

HS-SPME-GC-MS分析发芽糙米储藏过程中挥发性成分的变化

以水分含量为(14±0.5)％的发芽糙米为原料,取1 kg装入聚乙烯(PE)袋(15 cm×20 cm)密封后分别在湿度(65±3)％的4℃和35℃条件下储藏6个月.采用顶空固相微萃取(HS-SPME)和气相色谱-质谱联用(GC-MS)对4℃和35℃储藏及新鲜的发芽糙米中的挥发性物质进行提取、鉴定与分析.结果表明:发芽糙米挥发性成分主要有烃类、醛类和酯类,其次是醇类和酸类;随着储藏时间的延长,发芽糙米挥发性成分发生明显变化;4℃与35℃储藏下的发芽糙米挥发性成分种类、含量有差异性;在35℃下储藏的发芽糙米中的挥发性成分种类含量较4℃下有显著性增加.储藏6个月之后,变化较明显的挥发性成分有十六烷、十八烷、己醛、n-十六酸、2-乙基-1-己醇、乙酸乙酯.     

Analysis of volatile compounds of Antrodia camphorata in submerged culture using headspace solid-phase microextraction

In this work a headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography–mass spectrometry (GC–MS) and GC–olfactometry (GC–O) was developed to evaluate the profile of the volatile compounds that contribute to the aroma of Antrodia camphorata in submerged culture. For this purpose, the HS-SPME sampling method for the volatile compounds of A. camphorata in submerged culture was optimised by a D-optimal design. A HS extraction of the culture broth of A. camphorata followed by incubation on a carboxen/polydimethylsiloxane (CAR/PDMS) fibre during 31.8 min at 54.6 °C gave the most effective and accurate extraction of the volatile compounds. By the optimised method, a total of 49 volatile compounds were identified in culture broth of A. camphorata, while a total of 55 volatile compounds were identified in the mycelia. A series of C₈ aliphatic compounds (mushroom-like odour), several lactones (fruity odour) and l-linalool (citrus-like odour) were the most potent key odourant in both the mycelia and culture broth. This combined technique is fast, simple, sensitive, inexpensive and useful to monitor volatile compounds associated to A. camphorata.