Gas chromatographic-olfactometric characterization of aroma active compounds in sun-dried and vacuum-dried tarhana

The influence of drying methods on the aroma active volatiles of sun-dried tarhana (SDT) and vacuum-dried tarhana (VDT) were compared using headspace SPME, GC-O and GC-MS. Although vacuum drying reduced the total amount of volatiles as compared to SDT (total FID peak area), more aroma active material was retained with VDT (total olfactory peak area). Vacuum drying retained a greater number of aroma active components (41) whereas the sun-dried method retained only 23. Aldehydes were the largest single class of aroma compounds in both types of tarhana: 17 in VDT and 10 in SDT. Other differentiating aroma compounds include alcohols, terpenes, and phenols such as geraniol, terpinolene, and 4-vinylguaiacol among others. A total of 22 aroma active components were present in greater amounts in the VDT versus only four aroma compounds present in greater amounts in the SDT.     

Characterization of aroma-impact compounds in dry jujubes (Ziziphus jujube Mill.) by aroma extract dilution analysis (AEDA) and gas chromatography-mass spectrometer (GC-MS)

Aroma-impact compounds of dry jujubes obtained from Z. jujuba Mill. cv. “tangzao” (Y1), Z. jujuba Mill. cv. “muzao” (Y2), Z. jujuba Mill. cv. “lizao” (Y3), and Z. jujuba Mill. cv. “qingrunhongzao” (Y4) were analyzed by gas chromatography-olfactometry (GC-O). The result revealed 35, 29, 34, and 33 aroma-impact volatiles in the Y1, Y2, Y3, and Y4 samples, respectively. The compounds bearing the highest FD factor in each sample were (E)-2-hexenal, (E)-2-heptenal (FD = 256) for Y1, 2,3-butanedione, (E)-2-hexenal, 2,5-dimethylpyrazine, (E)-2-heptenal and β-damascenone (FD = 64) for Y2, 2,3-butanedione and β-damascenone (FD = 256) for Y3, and 2,5-dimethylpyrazine (FD = 256) for Y4.     

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.     

Analysis of the volatile profile and identification of odour-active compounds in Bayonne ham

The aim of this work was to reliably identify odour-active compounds in dry-cured ham using powerful analysis methods for the volatile fraction. For this purpose, dynamic headspace gas chromatography combined with eight-way olfactometry using a panel of eight sniffers was used. One- and two-dimensional gas chromatography coupled with mass spectrometry and (or) olfactometry were also used. More than 600 compounds from the volatile fraction of dry-cured ham were identified and their biochemical origins are discussed. They covered a wide diversity of structures and chemical functions. Only 29 of them proved odour-active. Comparison of the results of GC–O analysis with those obtained by orthonasal sniffing of the dry-cured ham helped to gain a better understanding of how these substances contributed to the overall aroma of the product. Thus, “Fruity–Floral”, “Green–Vegetable” or “Plastic–Chemical” odours intensively perceived by GC–O have been poorly perceived by orthonasal sniffing. By contrast, “Animal–Meat products” or “Butter–Lactic–Cheesy” odours have been much better perceived by orthonasal sniffing. These results indicate that to understand the interactions between odour-active compounds, experimental doping with carefully selected odour-active compounds will be necessary.     

Flavour and off-flavour compounds of Swiss Gruyère cheese. Evaluation of potent odorants

The flavour of a typical sample of Gruyère cheese and that of a Gruyère exhibiting a potato-like off-flavour was examined by instrumental and sensory analyses. Based on the results of dynamic headspace gas chromatography-mass spectrometry (DHGC/MS), aroma extract dilution analysis (AEDA) and gas chromatography-olfactometry of static headspace samples (GCO-H), 2-/3-methylbutanal, methional, dimethyltrisulphide, phenylacetaldehyde, 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, methanethiol, as well as butyric, 2-/3-methylbutyric and phenylacetic acid form the typical flavour of Gruyère cheese. The potato-like character of the sample showing an aroma defect, however, could not be attributed definitively to one of these compounds. Considering the results of DHGC/MS and AEDA, 2-ethyl-3,5-dimethylpyrazine and 2,3-diethyl-5-methylpyrazine could be the possible causes of the off-flavour.     

Volatile compounds and descriptive odor attributes in umbu (Spondias tuberosa) fruits during maturation

The umbu fruit is appreciated in north and northeast region of Brazil mainly because of its refreshing and acidic flavor. The objective of this work was to determine the volatile compounds in half-ripe and ripe stages of umbu fruit and to identify important characteristic compounds which could contribute for its aroma by performing sniffing evaluation of volatile extracts. The principal volatile compounds identified in the ripe umbu fruit pulp were 4-methyl-3-penten-2-one, ethyl benzene, 1-penten-3-one, 2-acetyl thiazone, p-xylene, limonene, 2,2-dimethyl 4-octenal, 3-hexanol, 2-nonanol, 1-nonanol, 2-pentanol, 2-octanol, 3-methylethyl 2-butanoate, butyl benzoate, 3-allyl cyclohexene, 2-acetyl furan, 2-hexyl furan, ??-caryophyllene and methyl pyrazine. A total of 37 volatile compounds were diagnosed with characteristic aroma attributes. The principal volatile compounds which could be responsible for the characteristic aroma of ripe umbu fruit pulp were ??-(Z)-ocimene, methyl pyrazine, 2-butyl-thiophene, methyl octanoate, 2-hexyl furan, 2-octanol, (E)-2-cyclohexen-1-one, 3-bromo-cyclohexene, 1-heptanol, 2-nonanol and 1-octanol.     

Volatile compounds captured through purge and trap technique in caja-umbu (Spondias sp.) fruits during maturation

This work identifies the volatile compounds present in the pulp of caja-umbu (Spondias sp.) fruits harvested at two different stages (half-ripe and ripe) of maturation. The volatiles were captured through purge and trap technique. The half-ripe caja-umbu fruit pulp contained 67 components among which the principal compounds, representing an area of 71.7% of chromatogram, were identified as β-caryophyllene (22.2%), 2-methyl butanal (19.3%), 2-hexanol (18.6%), ethyl butyrate (7.6%) and α-caryophyllene (3.9%). However, in the ripe caja-umbu fruit pulp, 70 compounds were detected among which 2-methyl butanal (28.4%), 2-hexanol (15.0%), β-caryophyllene (14.1%), ethyl butyrate (6.1%) and α-caryophyllene (2.4%) were prominent compounds. There were notable quantitative differences in prominent compounds such as β-caryophyllene and 2-hexanol which were quantitatively higher in half-ripe fruits while 2-methyl butanal known to possess characteristic pungent fresh fruit aroma increased with maturation, being relatively higher in its content in ripe fruits.     

Sensory and instrumental characterisation of commercial tomato varieties

Ten tomato varieties, i.e. Cencara, Daniella, Elena, Ibiza, Lemon Boy, Lucy, Melody, Perfecto, Raf and Rondello, were studied over two consecutive years by GC and GC-sniffing for their differences in flavour composition. Precautions were taken to avoid differences due to the growth conditions and stage of matu-rity. The aroma profiles obtained from dilutions of the extracts confirm the importance of most compounds previously reported as being key flavour compounds in tomatoes. Moreover, they outline a greater number of other key compounds which had not been identified or reported as such in the literature. Among them, 2-methoxyphenol, eugenol, decanal and geranylacetone were identified. Among 39 compounds quantified, 27 were found to permit discrimination between varieties both in 1992 and 1993. Six varieties were characterised in both years by specific flavour compositions. The differences between varieties is due to particular relative amounts of volatile compounds arising from the metabolism of aliphatic amino acids and carotenoids. Volatile compounds arising from each metabolic processes were found to be highly correlated with each other.     

白肋烟重要香味物质组成的研究

采用同时蒸馏萃取、气相色谱和气质谱联用法对国产 (湖北鹤峰、重庆奉节 )和进口 (巴西、津巴布韦和马拉维 )白肋烟中的酸性、碱性和中性香味物质进行了分析 ,共鉴定出 2 0 0种香味物质。文献检索表明 ,其中有 30种成分为烟草中尚未报道的化合物。采用内标法对白肋烟中重要的 2 6种碱性、39种中性和 15种酸性香味物质的含量 ,以及酸性、碱性和中性香味物质的总量进行了定量测定。分析结果表明 :在所分析的白肋烟样品中 ,(1)国内外白肋烟均含有相同种类数的香味物质 ,其不同点在于 :①国产白肋烟烟叶的酸性成分总量低于津巴布韦和马拉维白肋烟 ,而高于巴西白肋烟 ;②国产白肋烟的中性香味成分总量 (不计新植二烯 )高于津巴布韦和巴西白肋烟 ,略低于马拉维白肋烟 ;③国产白肋烟中的新植二烯含量明显高于国外白肋烟 ;④湖北白肋烟的碱性香味成分总量与巴西和津巴布韦白肋烟的接近 ,略高于马拉维白肋烟 ;⑤国产白肋烟中的杂环化合物 (吡啶、吡嗪和吡咯类 )和生物碱类化合物含量低于巴西和津巴布韦白肋烟 ;(2 )国内 2个主产区白肋烟香味物质的含量在酸、碱、中 3个集分中的差异比较突出 ,即除了湖北上部白肋烟酸性成分的总量低于重庆上部白肋烟的以外 ,湖北上部、中部和下部白肋烟中性和碱性香味成分 ,以及中     

Measurement of transport phenomena of volatile compounds: A review

Measurement of the transport phenomena of volatile compounds is a central preoccupation in food flavour and is the subject of the present paper. After a theoretical reminder concerning transport phenomena, the methods used for the measurement of diffusion and mass transfer of volatile compounds are described with their principles, main advantages and drawbacks. These methods are illustrated by some results obtained for flavoured model food products.

Several methods characterized by the type of diffusion coefficient measured, the method basis, the scale at which diffusion is measured and the means used to detect the diffusing molecule, are available to determine diffusion coefficients.

To study the impact of the different factors influencing aroma release, kinetic parameters extracted from release curves obtained by sampling and analysis of the gas phase can be measured and compared. The coherence between experimental conditions and mathematical models used to estimate the parameters is of major importance.     

An evaluation of methods for inoculating Listeria monocytogenes into butter for microbiological experimentation

The behaviour of Listeria monocytogenes Scott A was assessed when inoculated into butter using six different methods. The butter was made using a laboratory-scale butter churn to give consistency in the butter ingredients. No increase in count was seen using the 'stab' or 'contact' methods of butter inoculation. No inoculation method was found to be ideal for every inoculation experiment that may be required. However, it was concluded that the 'mix' and 'bead' methods were most appropriate if the 'cream' inoculation method could not be used.     

Use of polarography as a quality-control method for determining diacetyl in citrus and vegetable juices, yoghurt and butter

The determination of diacetyl permits the detection of microbial growth in the processing of citrus fruit before the appearance of other organoleptic, chemical or microbiological changes. It also makes it possible to detect a break in the cold chain during distribution and sale. The study proposed a polarographic method for the determination of diacetyl that allowed routine analysis with the aim of detecting possible contamination in the citrus juice manufacturing chain (orange and orange-carrot). The analytical performance of the method in terms of a linearity from 0 to 960 μg ml^-1, a recovery of 97 to 98%, a precision of 3.2 to 4.8%, and a sensitivity of 0.2 ng ml^-1 for juices indicated the robustness of the method. The same method was also applied to butter and yoghurt with detection limits of and 0.4 ng g^-1.     

Membrane separation technology for the reduction of alcoholic degree of a white model wine

The reduction of the alcoholic degree of a white model wine by means of membrane separation technology was studied in this work. Reverse osmosis and nanofiltration are the most promising processes for the production of wines with low alcohol content, because they can operate at low temperature and thereby preserve the aromatic profile of wine. Assuming that the rejection of the main wine compounds (i.e. acids, sugars and tannins) is very high, the aim of this research was to study the permeation of several characteristic aroma compounds in the white model wine. Permeation was conducted in batch retentate-recycling mode with two reverse osmosis and one nanofiltration membranes previously conditioned with a 12 ml/100 ml aqueous ethanol solution. Aroma compounds were identified by gas chromatography coupled to quadrupolar mass selective spectrometry. A mathematical model allowed calculation of the aroma compound concentrations in the retentate and permeate streams as a function of permeate volume and the concentration of solutes in the diluted final wine at 8 ml/100 ml ethanol concentration.     

The effects of butter characteristics on the growth of Listeria monocytogenes

The behaviour of Listeria monocytogenes was assessed after inoculation into butters made so that they exhibited a range of characteristics. Water droplet size and dispersion throughout the butter affected the ability of L. monocytogenes to grow, its rate of growth and the maximum population level achieved. Listeria monocytogenes was able to grow better in 'coarse' compared to 'fine' butter. Salt in the butter adversely affected growth of L. monocytogenes. However, slow growth was apparent at even higher levels (e.g. 2.1+%) of total salt. Growth of L. monocytogenes in butter at 8°C was comparable to that at 21°C.     

Changes in the aromatic composition of the Vitis vinifera grape Muscat Hamburg during ripening

A two-year study was carried out to determine the evolution of free and bound aromatic compounds of Muscat grape (sp. Vitis vinifera cv. Muscat Hamburg) during ripening. The most abundant free compounds detected were linalool, geraniol, citronellol, nerol, 3,7-dimethyl-1,5-octadien-3,7-diol (diendiol I) and 3,7-dimethyl-1,7-octadien-3,6-diol (diendiol II). In general, concentrations of the main free terpenols increased during grape development, except geraniol. In the glycosidically-bound fraction the major compounds were geraniol, linalool, citral, nerol, citronellol, α-terpineol, diendiol I, diendiol II, trans-furan linalool oxide (linaloloxide I), cis-furan linalool oxide (linaloloxide II), benzyl alcohol and 2-phenylethanol. At grape maturity, results showed a higher content of bound compounds than of free forms, with the exception of linalool, diendiol I, and diendiol II whose concentrations were greater in the free fraction, and limonene which was not detected in the bound fraction. On the basis Odour Activity Values, linalool was the most odour-active odorant. Other monoterpenes potentially contributing to Muscat aroma were rose oxide, citral, geraniol, nerol and citronellol.     

Stabilization of butter with deodorized rosemary extract

 The antioxidative activity of the ethanolic extract of deodorized rosemary (Rosmarinus officinalis L.) in butter was tested. The extract was added at two concentrations, 0.05 and 0.1%, to the cream before churning. The samples of isolated fat were stored at 60°C for 38 days and their peroxide values (PVs) determined periodically. The relative changes in the proton absorption patterns of the butter lipids during storage were monitored by nuclear magnetic resonance (NMR) spectroscopy. The samples treated with 0.05 and 0.1% extract had much longer induction periods than the control. A significant correlation (r = 0.980) was measured between the ratio of aliphatic to olefinic protons (R _ao) and the PVs of the butter fat. The deodorized ethanolic extract was also subjected to TLC separation on silica gel plates and UV spectral analysis. The UV spectrum of the extract had maxima at 286 and 328 nm. Six spots attributed to phenolic compounds were observed on the TLC plate. The extract also exhibited strong antioxidant activity in a β-carotene-linoleate model system. Received: 11 July 1997     

Stabilization of butter with deodorized rosemary extract

 The antioxidative activity of the ethanolic extract of deodorized rosemary (Rosmarinus officinalis L.) in butter was tested. The extract was added at two concentrations, 0.05 and 0.1%, to the cream before churning. The samples of isolated fat were stored at 60°C for 38 days and their peroxide values (PVs) determined periodically. The relative changes in the proton absorption patterns of the butter lipids during storage were monitored by nuclear magnetic resonance (NMR) spectroscopy. The samples treated with 0.05 and 0.1% extract had much longer induction periods than the control. A significant correlation (r = 0.980) was measured between the ratio of aliphatic to olefinic protons (R _ao) and the PVs of the butter fat. The deodorized ethanolic extract was also subjected to TLC separation on silica gel plates and UV spectral analysis. The UV spectrum of the extract had maxima at 286 and 328 nm. Six spots attributed to phenolic compounds were observed on the TLC plate. The extract also exhibited strong antioxidant activity in a β-carotene-linoleate model system. Received: 11 July 1997     

Characterisation of the key aroma compounds in a freshly reconstituted orange juice from concentrate

Application of an aroma extract dilution analysis on the entire volatile fraction isolated from an orange juice freshly reconstituted from concentrate revealed 40 odour-active constituents in the flavour dilution (FD) factor range of 4–2,048. Among them, ethyl butanoate and linalool showed the highest FD factor of 2,048, followed by octanal with an FD factor of 512. Thirty-six of the 40 odour-active compounds detected could be identified, all of which have previously been reported as volatile constituents of various orange juices. Quantification of 17 key odorants by stable isotope dilution assays followed by a calculation of odour activity values (OAVs) on the basis of odour thresholds in water or citrate buffer (pH 3.8), respectively, revealed the following most important odorants in the overall aroma of the freshly reconstituted juice: (R/S)-linalool, (R)-limonene and (S)-ethyl 2-methylbutanoate with the highest OAVs (>1,000) followed by octanal, (R)-α-pinene, ethyl butanoate, myrcene, acetaldehyde, decanal and (E)-β-damascenone with OAVs > 100. A model mixture containing all 14 aroma compounds with OAVs > 1 in their actual concentrations in the juice showed a good similarity with the aroma of the original orange juice under investigation, thus corroborating that the key odorants of a freshly reconstituted orange juice were characterised for the first time.