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1.
The volatile composition of the headspace from Citrus unshiu Marcov. forma Miyagawa-wase blossom was investigated. The volatile constituents were absorbed by a solid-phase microextraction (SPME) fiber and directly transferred to a GC-MS. Volatile compositional changes of C. unshiu blossom prepared via different drying methods (shade, microwave, and freeze-drying methods) were also determined. A total of 96 volatile constituents were confirmed in the headspace from these samples. Monoterpene hydrocarbons were prominent in the headspace volatiles of C. unshiu blossom: fresh, 84.1%; shade-dried, 60.0%; microwave-dried, 88.4%; and freeze-dried, 29.9%. p-Cymene (23.3%) was the most abundant component in the headspace of fresh C. unshiu blossom; gamma-terpinene was the most abundant in shade- and microwave-dried samples (26.8 and 31.2%, respectively) and beta-caryophyllene (10.5%) in freeze-dried sample. By using an electronic nose consisting of six metal oxide sensors, principal component analysis of the volatile compounds showed a clear aroma discrimination of the fresh and all dried blossom samples.  相似文献   

2.
The use of solid-phase microextraction (SPME) coupled with isotope ratio mass spectrometry (IRMS) for the analysis of flavor compounds produced by lactic acid bacteria has been evaluated using both liquid and headspace sampling modes. Initially, it was necessary to optimize the conditions for the SPME extraction of flavors-diacetyl and acetoin-in standard aqueous solutions. The effects of salt, headspace versus liquid sampling, and coating phase were tested. Second, the suitability of the coupling of SPME and gas chromatography-combustion interface-IRMS (GC-C-IRMS) for the determination of delta(13)C values was assessed. It is shown that neither the analyte concentration nor the period of fiber exposure has an effect on the delta(13)C values. Finally, having verified that there are no matrix effects from the fermentation medium, it is reported for the first time that flavor compounds can be extracted directly from culture supernatant by SPME and their delta(13)C values can be obtained by GC-C-IRMS.  相似文献   

3.
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4.
Comparisons were made between the aroma volatiles of the yellow-fleshed kiwifruit, "Hort16A", at two different stages of eating ripeness: firm and soft. The firm fruit contained a small number of aroma compounds that the soft fruit did not contain. In general, however, the largest difference between the two firmness categories was in the levels of esters, with the soft fruit containing higher concentrations and a larger number of esters than the firm fruit. In vitro analysis directly after maceration using atmospheric pressure chemical ionization mass spectrometry (APCI-MS) showed the relative importance of the most intense aromas between fruit at the two different firmness stages and was used to compare the release rates of aromas. A comparison of the aroma concentrations from gas chromatography mass spectrometry (GC-MS) and APCI-MS headspace analyses showed that the APCI-MS headspace showed less bias toward enzymatically generated lipid degradation compounds. A GC-sniffing study showed that many of the most intense compounds, acetaldehyde, hexanal, ethyl butanoate, and (E)-2-hexenal but not ethanol, showed odor activity in macerated fruit. In addition, dimethyl sulfide (DMS), a volatile present at very low levels in the fruit, also appeared to be an important contributor to the odor. In vivo analyses also showed much higher levels of aroma compounds in the soft fruit compared to the firm fruit, with evidence of persistence of some compounds, including DMS. There were a number of similarities between the breath profiles of the two panelists, which confirmed the importance of DMS in "Hort16A" aroma.  相似文献   

5.
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6.
The sensory and health properties of virgin olive oil (VOO) are highly related to its volatile and phenolic composition. Oxygen control in the pastes during malaxation may be a new technological parameter to regulate enzymatic activities, such as polyphenoloxidase, peroxidase, and lipoxygenase, which affect the phenolic and volatile composition of VOO. In this work, we monitored CO2 and O2 concentrations during industrial-scale olive paste malaxation with various initial O2 concentrations within the malaxer headspace. Results show that the O2 concentration in the malaxer headspace did not affect CO2 production during processing, whereas a strong influence was observed on the changes of the phenolic composition of olive pastes and VOOs, with high correlation coefficient for the total phenols (R = 0.94), especially for oleuropein and demethyloleuropein derivatives (R = 0.81). In contrast, aroma production during malaxation was minimally affected by the O2 concentration in the malaxer headspace.  相似文献   

7.
By gel filtration on Sephadex G-50 and G-75, we investigated the changes in the composition and ratio of the molecular fractions of humic acids under the influence of native soil microbial complexes. The highest degree of decomposition of the initial humic acid was observed when ammonium nitrate was used as a source of additional energy in the mineral nutrient medium without a yeast extract. The appearance of a low molecular fraction of organic substances on chromatograms may be associated with the synthesis by bacteria of simple organic substances on the medium with humic acids as a single source of carbon.  相似文献   

8.
This study was conducted to determine the volatile flavor composition of fresh changpo (Acorus calamus var. angustatus Bess) leaves quantitatively and qualitatively by use of two internal standards and to determine which volatile compounds are primarily responsible for the aroma of this aquatic herb. The headspace composition of fresh changpo leaves was also analyzed by a solid-phase microextraction method. Aroma extract dilution analysis (AEDA) and sniffing test by gas chromatography-olfactometry were used for the detection of aroma-active compounds of this herb. According to the instrumental analyses of the changpo oil, octanoic acid (49.13%), alpha-cedrene (16.71%), alpha-phellandrene (4.46%), and gamma-elemene (3.75%) were the most abundant compounds. n-Butylidene dihydrophthalide (8.61%), trans,trans-farnesyl acetate (7.29%), and trans-2-dodecenal (7%) were the main components of changpo headspace. cis-beta-Farnesene was evaluated as the key aroma compound of this herb from results of AEDA and sniffing test.  相似文献   

9.
Methyl bromide (MB, bromomethane) is determined in a variety of foods by headspace capillary gas chromatography with electron capture detection. The comminuted food sample as an aqueous sodium sulfate slurry is equilibrated with stirring for 1 h at room temperature before a 1 mL headspace aliquot is removed and injected using a modified on-column syringe needle. Methyl bromide is cryogenically focussed at -60 degrees C and then eluted by temperature programming. The procedure requires blending of soft samples, e.g. raisins, prunes, or oranges, and ultrasonic homogenization of hard samples, e.g. wheat, cocoa beans, corn, or nuts, with portions of water and ice so the final temperature of the food-water slurry is less than 1 degree C. A 20 g aliquot (4 g food) is then added to a cold headspace vial containing 4 g sodium sulfate. Losses of MB during a 3.5 min ultrasonic homogenization of wheat were 11% at 0.95 ppb and 4.4% at 4.8 ppb. For flour, cocoa, and finely divided spices, which do not require blending, 4 g is added to the cold headspace vial containing 16 mL cold water and 4 g sodium sulfate. Studies show that comminution of wheat or peanuts must be carried out to release MB trapped within the food so the headspace equilibrium can be attained in 1 h as well as to obtain homogeneous samples and representative sampling. No interferences were noted with the above foods or with many grain-based baking mixes analyzed.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

10.
A sampling method for determining the volatile terpenoid composition from single needles of seven Tsuga species was developed using headspace solid-phase microextraction (SPME). A reproducible sampling method for the volatile components was generated by examination of sample storage, method of needle cutting, and headspace sampling duration. Following SPME collection of the volatile compounds from the seven Tsuga species, gas chromatography/ion-trap mass spectrometry was used to identify 51 terpenoids present in the needle headspace. A semiquantitative method was devised to express individual terpenoid amounts as a percentage of all of the identified peaks in the chromatogram. The semiquantitative results permitted facile interspecies comparison using principal component analysis. Two components were able to account for 90% of the variance and were interpreted as a "species" component and a "resistance/susceptibility" component. Three interspecies groupings were evident from the principal component analysis: (1) Tsuga canadensis and Tsuga caroliniana; (2) Tsuga chinesnsis, Tsuga diversifolia, Tsuga heterophylla, and Tsuga sieboldii; and (3) Tsuga mertensiana. The finding that T. mertensiana was grouped alone and far removed from the other species adds to the morphological evidence that this species should be segregated from other Tsuga.  相似文献   

11.
The leaves and stems of the Rooibos plant ( Aspalathus linearis) are used for the production of an herbal tea known for its health promoting properties, which have been linked to its flavonoid content but which is substantially reduced by the traditional processing method employed. Selected food-grade fungi were screened for their potential to improve the yield of soluble matter extracted from rooibos plant material. Fungal cocktails of hydrolyzing enzymes enhanced either the yield of soluble solids ( Lentinula edodes and Rhizopus oryzae cultured in yeast peptone-wheat straw medium) or the yield in antioxidants from fermented rooibos ( R. oryzae cultured in potato dextrose or yeast peptone-wheat straw medium). When applied to green rooibos, L. edodes (cultured in yeast peptone-wheat straw medium) enhanced the release of soluble solids as well as color formation, leading to semifermented rooibos with a relatively high aspalathin content, compared to fermented rooibos.  相似文献   

12.
In the first part of this work, the analysis of the polyphenolic compounds remaining in the wine after different contact times with yeast lees during simulation of red wine aging was undertaken. To achieve a more precise view of the wine polyphenols adsorbed on lees during red wine aging and to establish a clear balance between adsorbed and remnant polyphenol compounds, the specific analysis of the chemical composition of the adsorbed polyphenolic compounds (condensed tannins and anthocyanins) after their partial desorbtion from yeast lees by denaturation treatments was realized in the second part of the study. The total recovery of polyphenol compounds from yeast lees was not complete, since a rather important part of the initial wine colored polyphenols, especially those with a dominant blue color component, remained strongly adsorbed on yeast lees, as monitored by color tristimulus and reflectance spectra measurements. All anthocyanins were recovered at a rather high percentage (about 62%), and it was demonstrated that they were not adsorbed in relation with their sole polarity. Very few monomeric phenolic compounds were extracted from yeast lees. With the use of drastic denaturing treatments, the total recovery of condensed tannins reached 83%. Such tannins extracted from yeast lees exhibited very high polymeric size and a rather high percentage of galloylated residues by comparison with initial wine tannins, indicating that nonpolar tannins were preferentially desorbed from yeast lees by the extraction treatments.  相似文献   

13.
The static headspace composition of sunflower oil throughout the oxidation process at 70 degrees C with circulating air is studied by means of solid-phase microextraction followed by gas chromatography-mass spectrometry (SPME-GC-MS); at the same time the liquid phase of the same oil is studied by means of Fourier transform infrared (FTIR) spectroscopy. Each technique provides complementary information about the process; FITR spectroscopy detects changes in the functional groups of the liquid matrix in a global way and SPME/GC-MS provides information about the different components present in the volatile phase during the oxidation process. Concordance between the timing of the changes produced in both liquid and gaseous phases is observed, as well as agreement and complementarity in the results obtained from both phases. The formation of some well-known genotoxic and cytotoxic oxygenated aldehydes in this process and their presence in the oil headspace are proved.  相似文献   

14.
Solid-phase microextraction (SPME) fibers were evaluated for their ability to adsorb volatile flavor compounds under various conditions with coffee and aqueous flavored solutions. Experiments comparing different fibers showed that poly(dimethylsiloxane)/divinylbenzene had the highest overall sensitivity. Carboxen/poly(dimethylsiloxane) was the most sensitive to small molecules and acids. As the concentrations of compounds increased, the quantitative linear range was exceeded as shown by competition effects with 2-isobutyl-3-methoxypyrazine at concentrations above 1 ppm. A method based on a short-time sampling of the headspace (1 min) was shown to better represent the equilibrium headspace concentration. Analysis of coffee brew with a 1-min headspace adsorption time was verified to be within the linear range for most compounds and thus appropriate for relative headspace quantification. Absolute quantification of volatiles, using isotope dilution assays (IDA), is not subject to biases caused by excess compound concentrations or complex matrices. The degradation of coffee aroma volatiles during storage was followed by relative headspace measurements and absolute quantifications. Both methods gave similar values for 3-methylbutanal, 4-ethylguaiacol, and 2,3-pentanedione. Acetic acid, however, gave higher values during storage upon relative headspace measurements due to concurrent pH decreases that were not seen with IDA.  相似文献   

15.
Significant tomato matrix effects on the volatility of certain fresh tomato odorants were found. The concentrations of odorants such as (E,E)-2,4-decadienal, beta-damascenone, and beta-ionone, in crushed fresh tomato fruit obtained by solid-phase microextraction (SPME), resulting from a tomato matrix calibration curve were 5.5-, 2-, and 12-fold higher, respectively, than those calculated by calibration based on buffer solutions. Static headspace analyses indicated that, in most cases, the tomato matrix significantly retains the odorants relative to the buffer solution. Thus, the concentration of odorants in the headspace of tomato is lower than expected compared to a simple matrix such as buffer. CaCl(2), although needed in crushed fruit tissue to block enzymatic activity, was found to interact specifically with 2-isobutylthiazole, reducing its content in the headspace by at least 6-fold. If a matrix effect is found, analysis of the odorant molecule contents in the headspace rather than in the food is recommended in order to better evaluate their access to the olfactory receptors.  相似文献   

16.
Several Rhizobium spp were tested for chemotaxis using a soft agar assay. Bacteria migrated in chemotactic bands in response to substances present in the agar medium. R. japonicum S-110 formed chemotactic bands in response to l-arabinose, l-canavanine, and yeast extract but not to several other common compounds, including several amino acids and sugars. These results suggested that simple compounds present in legume root exudates may attract these bacteria and aid in their rhizosphere accumulation and, thus, in the nodulation process. A slow-migrating mutant of R. japonicum S-110 was isolated. Microscopic examination showed that mutant populations had a much lower proportion of motile cells than did wild-type populations. Greenhouse nodulation tests, in which mutant and wild-type cells were mixed and used as inoculum, indicated that the mutant had less nodulation potential.  相似文献   

17.
针对西安市金盆水库软弱变质岩边坡的地质条件,在细致分析黏土矿物的主要特性及形成机制的基础上,从微观到宏观的不同尺度,系统研究了黏土矿物对软弱变质岩边坡失稳的影响.结果表明,软弱变质岩成因复杂,矿物成分多样,水稳定性差,易于生成黏土矿物;而次生黏土矿物的形成将引起源矿物、矿物集合体及岩块特性的显著变化,诱发岩石向松散介质转化,并触发黏土矿物在宏观结构面中的聚集和泥化夹层的形成,导致结构面及岩体强度衰减,进而促进边坡变形破坏,对边坡演化及失稳的贡献显著.  相似文献   

18.
The potent aroma compound rose oxide was quantified in several white wines by a headspace solid-phase microextration stable isotope dilution assay (HS-SPME-SIDA) and the enantiomeric ratios of the cis diastereomers were determined by enantioselective capillary GC. The most odor-active stereoisomer (23)-cis-rose oxide was detectable in all investigated white wines ranging from 0.2 to 12 microg/L. However, its contribution to the overall aroma in some white wine varieties can be neglected as indicated by a low odor activity value (OAV). The highest concentrations were found in Gewürztraminer wines, confirming the importance of rose oxide as a varietal aroma compound in this variety. Surprisingly, the enantiomeric ratio of cis-rose oxide in all investigated wines was substantially lower than in nonfermented musts and in some wines almost racemic cis-rose oxide was detected. Fermentation studies with a model must that contained deuterated water revealed that yeast is capable of reducing the precursor 3,7-dimethyl octa-2,5-dien-1,7-diol (geranyl diol I) yielding 3,7-dimethyl-5-octen-1,7-diol (citronellyl diol I) that gives rise to cis- and trans-rose oxide after acid catalyzed cylization. The deuterium labeling pattern of the resulting rose oxide stereoisomers and a clearly detectable kinetic isotope effect indicate that at least two different reductive pathways in yeast exist that yield cis-rose oxide with different enantiomeric ratios altering the genuine enantiomeric ratio in grape musts. The presence of (+)-cis-rose oxides in wines can therefore be attributed to the reductive yeast metabolism during fermentation. This observation corroborates recent findings that the modification of terpene derived varietal aroma is an integral part of yeast metabolism and not only a simple hydrolytical process.  相似文献   

19.
The mixture of bark and gum obtained after size-grading of Siam benzoin gum was studied to establish its potential application as a valuable new grade of the balsamic resin. An analysis of its volatile constituents by means of static headspace and SPME led to the identification of 26 and 50 compounds, respectively. Significant differences were observed in both the headspace composition and olfactory properties of the byproduct as compared to those of Siam benzoin gum. This prompted the further analysis of its volatile extract and its resinoid by GC techniques, resulting in the identification of 60 (99.5%) and 16 (89.1%) components, respectively. To examine the influence of bark pieces, different extracts obtained from the raw material and from a sorted sample were analyzed by GC and HPLC techniques. The chemical compositions and the yields determined for the two resinoids lead to the conclusion that this harvesting byproduct is a new grade of Siam benzoin gum, providing interesting olfactory notes that differ from those of other grades.  相似文献   

20.
A comparative study of the storage and reuse of immobilized yeast cells on apple pieces, kissiris, and gamma-alumina was carried out. The immobilized biocatalysts were allowed to remain in the fermented alcoholic liquid after the end of each fermentation batch for extended periods at 30 degrees C before reactivation in batch fermentation for wine-making. The results showed that the biocatalysts were able to reactivate and ferment after successively increased periods of storage compared to free cell systems both on glucose medium and on grape must. In glucose medium, apple-, kissiris-, and gamma-alumina-supported biocatalysts reactivated after 120, 80, and 83 days, respectively. Possible storage periods for grape must were lower but remained high. Immobilized yeast biocatalyst on apple pieces produced wines with an improved volatiles composition compared to kissiris- and gamma-alumina-supported biocatalysts. There were no significant negative effects on the fermentation activity and volatile byproduct composition.  相似文献   

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