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1.
The headspace volatiles produced from a phosphate-buffered solution (pH 5) of cysteine and a 1 + 1 mixture of ribose and [(13)C(5)]ribose, heated at 95 degrees C for 4 h, were examined by headspace SPME in combination with GC-MS. MS data indicated that fragmentation of ribose did not play a significant role in the formation of the sulfur aroma compounds 2-methyl-3-furanthiol, 2-furfurylthiol, and 3-mercapto-2-pentanone in which the carbon skeleton of ribose remained intact. The methylfuran moiety of 2-methyl-3-(methylthio)furan originated from ribose, whereas the methylthio carbon atoms came partly from ribose and partly from cysteine. In 3-mercapto-2-butanone one carbon unit was split from the ribose chain. On the other hand, all carbon atoms in 3-thiophenethiol stemmed from cysteine. In another trial cysteine, 4-hydroxy-5-methyl-3(2H)-furanone and [(13)C(5)]ribose were reacted under the same conditions. The resulting 2-methyl-3-furanthiol was mainly (13)C(5)-labeled, suggesting that it stems from ribose and that 4-hydroxy-5-methyl-3(2H)-furanone is unimportant as an intermediate. Whereas 2-mercapto-3-pentanone was found unlabeled and hence originated from 4-hydroxy-5-methyl-3(2H)-furanone, its isomer 3-mercapto-2-pentanone was formed from both 4-hydroxy-5-methyl-3(2H)-furanone and ribose. A new reaction pathway from ribose via its 1,4-dideoxyosone is proposed, which explains both the formation of 2-methyl-3-furanthiol without 4-hydroxy-5-methyl-3(2H)-furanone as an intermediate and a new way to form 3-mercapto-2-pentanone.  相似文献   

2.
Eleven odor-active thiols, namely, 2-methyl-1-propene-1-thiol, (Z)-3-methyl-1-butene-1-thiol, (E)-3-methyl-1-butene-1-thiol, (Z)-2-methyl-1-butene-1-thiol, (E)-2-methyl-1-butene-1-thiol, 2-methyl-3-furanthiol, 3-mercapto-2-pentanone, 2-mercapto-3-pentanone, 4-mercapto-3-hexanone, 3-mercapto-3-methylbutyl formate, and 2-methyl-3-thiophenethiol, recently identified in an extract prepared from white sesame seeds, were quantitated in sesame using stable isotope dilution analyses. For that purpose, the following deuterium-labeled compounds were synthesized and used as internal standards in the quantitation assays: [2H6]-2-methyl-1-propene-1-thiol, [2H3]-(E)- and [2H3]-(Z)-2-methyl-1-butene-1-thiol, [2H3]-2-methyl-3-furanthiol, [2H2]-3-mercapto-2-pentanone, [2H3]-4-mercapto-3-hexanone, [2H6]-3-mercapto-3-methylbutyl formate, and [2H3]-2-methyl-3-thiophenethiol. On the basis of the results obtained, odor activity values (OAVs) were calculated as ratio of the concentration and odor threshold of the individual compounds in cooking oil. According to their high OAVs, particularly the 3-methyl-1-butene-1-thiols (OAV: 2400) and the 2-methyl-1-butene-1-thiols (OAV: 960) were identified as the most odor-active compounds in pan-roasted white sesame seeds. These compounds were therefore suggested to be mainly responsible for the characteristic but rather unstable sulfury aroma of freshly pan-roasted white sesame seeds.  相似文献   

3.
The volatiles formed from [1-(13)C]-ribose and cysteine during 4 h at 95 degrees C in aqueous phosphate buffer (pH 5) were analyzed by headspace SPME in combination with GC-MS. The extent and position of the labeling were determined using MS data. The identified volatiles comprised sulfur compounds such as 2-[(13)C]methyl-3-furanthiol, 2-[(13)CH(2)]furfurylthiol, [1-(13)C]-3-mercaptopentan-2-one, [1-(13)C]-3-mercaptobutan-2-one, [4-(13)C]-3-mercaptobutan-2-one, and 3-mercaptobutan-2-one. The results confirm furan-2-carbaldehyde as an intermediate of 2-furfurylthiol, as well as 1,4-dideoxypento-2,3-diulose as an intermediate of 2-methyl-3-furanthiol and 3-mercaptopentan-2-one. Loss of the C-1 and C-5 carbon moieties during the formation of 3-mercaptobutan-2-one suggests two different mechanisms leading to the key intermediate butane-2,3-dione.  相似文献   

4.
Thiamin hydrochloride was thermally degraded in phosphate buffer (pH 6.5) at 110 degrees C for 2 h. A major decomposition product was isolated by column chromatography and structurally identified by spectrometric techniques ((1)H NMR, (13)C NMR, 2D NMR, and MS) as 2-methyl-4-amino-5-(2-methyl-3-furylthiomethyl)pyrimidine (MAMP). The possible formation pathway of MAMP was studied using two model systems. It is proposed that MAMP is formed by nucleophilic attack of 2-methyl-3-furanthiol on the thiamin.  相似文献   

5.
Characterization of the most odor-active compounds of Iberian ham headspace   总被引：11，自引：0，他引：11  
Gas chromatography-olfactometry (GC-O) based on detection frequency (DF) was used to characterize the most odor-active compounds from the headspace of Iberian ham. Twenty-eight odorants were identified by GC-O on two capillary columns, including aldehydes (11), sulfur-containing compounds (7), ketones (5), nitrogen-containing compounds (2), esters (2), and an alcohol. Among them, the highest odor potencies (DF values) were found for 2-methyl-3-furanthiol, 2-heptanone, 3-methylbutanal, methanethiol, hexanal, hydrogen sulfide, 1-penten-3-one, 2-methylpropanal, ethyl 2-methylbutyrate, and (E)-2-hexenal. Nine of the 28 most odor-active compounds were identified for the first time as aroma components of dry-cured ham, including hydrogen sulfide, 1-penten-3-one, (Z)-3-hexenal, 1-octen-3-one, and the meaty-smelling compounds 2-methyl-3-furanthiol, 2-furfurylthiol, 3-mercapto-2-pentanone, 2-acetyl-1-pyrroline, and 2-propionyl-1-pyrroline.  相似文献   

6.
Comparative aroma dilution analyses of the headspaces of aqueous solutions containing either the total volatiles isolated from a fresh coffee brew, or these volatiles remixed with the melanoidins isolated from coffee brew, revealed a drastic decrease in the concentrations of the odorous thiols 2-furfurylthiol, 3-methyl-2-butenthiol, 3-mercapto-3-methylbutyl formate, 2-methyl-3-furanthiol, and methanethiol when melanoidins were present. Among these thiols, 2-furfurylthiol was affected the most: e.g., its concentration decreased by a factor of 16 upon addition of melanoidins. This was accompanied by a decrease in the overall roasty-sulfury aroma. Quantitations performed by means of stable isotope dilution assays confirmed the rapid loss of all thiols with increasing time while keeping the coffee brew warm in a thermos flask. Using [2H2]-2-furfurylthiol as an example, [2H]-NMR and LC/MS spectroscopy gave strong evidence that thiols are covalently bound to the coffee melanoidins via Maillard-derived pyrazinium compounds formed as oxidation products of 1,4-bis-(5-amino-5-carboxy-1-pentyl)pyrazinium radical cations (CROSSPY). Using synthetic 1,4-diethyl diquaternary pyrazinium ions and 2-furfurylthiol, it was shown that 2-(2-furyl)methylthio-1,4-dihydro-pyrazines, bis[2-(2-furyl)methylthio]-1,4-dihydro-pyrazines, and 2-(2-furyl)methylthio-hydroxy-1,4-dihydro-pyrazines were formed as the primary reaction products. Similar results were obtained for models in which either 1,4-diethyl diquaternary pyrazinium ions were substituted by Nalpha-acetyl-L-lysine/glycolaldehyde, or the 2-furfurylthiol by 2-methyl-3-furanthiol and 3-mercapto-3-methylbutyl formate. On the basis of these results it can be concluded that the CROSSPY-derived pyrazinium intermediates are involved in the rapid covalent binding of odorous thiols to melanoidins, and, consequently, are responsible for the decrease in the sulfury-roasty odor quality observed shortly after preparation of the coffee brew.  相似文献   

7.
Polyfunctional thiols are known to have a strong impact on the overall aroma of many fermented foods. Surprisingly, very little data is available on their occurrence in beer. A specific extraction with p-hydroxymercuribenzoic acid was performed on four different fresh light-protected lager beers. gas chromatography-olfactometry, gas chromatography-mass spectrometry, and gas chromatography-pulsed-flame photometer detector analyses of the extracts revealed the presence of more than 10 polyfunctional thiols. All of them were absent from wort, suggesting a key role of the H(2)S excreted by yeasts. 3-Methyl-2-buten-1-thiol, 2-mercapto-3-methylbutanol, 3-mercapto-3-methylbutanol seem to be created from hop allylic alcohols via four different mechanisms: nucleophilic substitution, addition-elimination, and radical anti-Markovnikov or electrophilic Markovnikov additions. 1,4 Addition of hydrogen sulfide to wort alpha,beta-unsaturated aldehydes or ketones may explain the synthesis of 1-mercapto-3-pentanol, 3-mercaptohexanol, and 4-mercapto-4-methyl-2-pentanone through fermentation. Finally, 2-mercaptoethanol, 3-mercaptopropanol, and their corresponding acetates may derive from Ehrlich degradation of sulfur amino acids, while 2-methyl-3-furanthiol should be logically issued from Maillard reactions.  相似文献   

8.
4-Mercapto-4-methyl-2-pentanone is one of the most strongly contributing odorants in the volatile fraction of a Japanese green tea (sen-cha) infusion, and on the basis of the results of an aroma extract dilution analysis, the contribution of this compound to the flavor of the sen-cha infusion varied according to the degree of heating of the tea leaves during the roasting process. The concentration of this odorant in the sen-cha infusion, as with other roasty odorants, increased with the increasing roasting temperature. However, the slope of the increase curve differed with the odor compound, and even if roasting was done at a low temperature, at which the other roasty odorants hardly increased, 4-mercapto-4-methyl-2-pentanone still increased and reached a maximum at 112 degrees C. On the other hand, the amount of 4-mercapto-4-methyl-2-pentanone in sen-cha was a maximum in the first crop, then decreasing in the order of the second and third crops. These results suggested that the amount of 4-mercapto-4-methyl-2-pentanone was closely involved with the quality of sen-cha and that the concentration was dependent on the roasting conditions for the green tea leaves, which might be accompanied by an enzymatic reaction.  相似文献   

9.
Defatted soybean meal was converted into enzyme-hydrolyzed vegetable protein (E-HVP) using the proteolytic enzyme Flavorzyme. Total free amino acids increased by 40-fold after enzyme hydrolysis, with leucine being the most abundant, followed by phenylalanine, lysine, glutamine/glutamic acid, and alanine. Volatile components from a meatlike process flavoring made from E-HVP were isolated by direct solvent extraction (DSE)-high vacuum transfer (HVT), dynamic headspace sampling and static headspace sampling and analyzed by gas chromatography (GC)-mass spectrometry and GC-olfactometry. Aroma extract dilution analysis was used to establish a flavor dilution chromatogram of the DSE-HVT extract. Results of these complementary techniques indicated the importance of odorants of high (hydrogen sulfide and methanethiol), intermediate (2-methyl-3-furanthiol, 3-mercapto-2-pentanone, 2-furanmethanethiol, and 3-(methylthiol)propanal) and low volatility (maltol and Furaneol) in the overall aroma of the meatlike process flavoring.  相似文献   

10.
Aroma-active compounds from a beeflike process flavor, produced by extrusion of enzyme-hydrolyzed vegetable protein (E-HVP), were analyzed using aroma extract dilution analysis. The number of aroma-active compounds and the aroma intensity were increased by the addition of aroma precursors prior to extrusion. The most intense compound was 2-methyl-3-furanthiol having a cooked rice/vitamin-like/meaty aroma note. Several sulfur-containing furans, such as 2-methyl-3-(methylthio)furan, 2-methyl-3-(methyldithio)furan, and bis(2-methylfuryl)disulfide, were detected with high flavor dilution (FD) factors. Some pyrazines, such as 2-ethyl-3,5-dimethylpyrazine, 2,6-diethylpyrazine, and 3,5-diethyl-2-methylpyrazine, also had high FD factors. It is hypothesized that sulfur-containing amino acids and thiamin were important precursors in aroma formation in process flavor from E-HVP.  相似文献   

11.
The flavor stability of an aqueous solution of a savory model process flavoring based on ribose and cysteine was investigated during accelerated storage at 50 degrees C. Of the three sulfur-containing flavor-impact components investigated, 2-methyl-3-furanthiol was found to be the least stable (59% decrease/24 h), and it was followed by 2-furfurylthiol (28% decrease/24 h), 2-mercapto-3-butanone (14% decrease/24 h), and 2,5-dimethyl-4-hydroxy-3(2H)-furanone (max. 10% decrease/24 h). Both cysteine and ribose were found to affect the stability of various flavor compounds. A mechanism for the instability of 2-methyl-3-furanthiol is proposed, and was confirmed by H-D exchange experiments.  相似文献   

12.
Mixtures of cysteine, reducing sugar (xylose or glucose), and starch were extrusion cooked using feed pH values of 5.5, 6.5, and 7.5 and target die temperatures of 120, 150, and 180 degrees C. Volatile compounds were isolated by headspace trapping onto Tenax and analyzed by gas chromatography--mass spectrometry. Eighty and 38 compounds, respectively, were identified from extrudates prepared using glucose and xylose. Amounts of most compounds increased with temperature and pH. Aliphatic sulfur compounds, thiophenes, pyrazines, and thiazoles were the most abundant chemical classes for the glucose samples, whereas for xylose extrudates highest levels were obtained for non-sulfur-containing furans, thiophenes, sulfur-containing furans, and pyrazines. 2-Furanmethanethiol and 2-methyl-3-furanthiol were present in extrudates prepared using both sugars, but levels were higher in xylose samples. The profiles of reaction products were different from those obtained from aqueous or reduced-moisture systems based on cysteine and either glucose or ribose.  相似文献   

13.
Model orange juice solutions containing 0.024 mM thiamin hydrochloride were stored for up to 8 weeks at 35 degrees C in amber glass containers. Volatiles were evaluated, primarily, using gas chromatography (GC) with olfactometry but also with flame ionization detector, pulsed-flame photometer detector (PFPD) (sulfur specific), and MS detection. Both 2-methyl-3-furanthiol (MFT) and its dimer, bis(2-methyl-3-furyl) disulfide (MFT-MFT) were identified thus confirming that thiamin could serve as the precursor to these potent off-flavors in thermally degraded citrus juices. Thirteen aroma active components were observed. MFT and MFT-MFT were observed after only a few days storage, and produced 33% of the total aroma activity after 7 d storage. Both compounds were observed olfactometrically earlier than they could be detected using PFPD. Other aroma-active compounds included 4,5-dimethylthiazole (skunky, earthy), 3-thiophenethiol (meaty, cooked), 2-methyl-4,5-dihydro-3(2H)-thiophenone (sour-fruity, musty, green), 2-acethylthiophene (burnt), 2-formyl-5-methylthiophene (meaty), and 2-methyl-3-(methyldithio) furan (meaty).  相似文献   

14.
5-Hydroxy-3-mercapto-2-pentanone is claimed in the scientific literature as a key intermediate in the degradation of thiamine and the related generation of aroma compounds; however, there are no analytical NMR and MS data available. We have identified the compound in a thermally treated mixture of thiamine, cysteine, and xylose and characterized it by MS and NMR.  相似文献   

15.
Enzymatic hydrolysis of S-3-(2-methylfuryl) thioacetate and S-2-furfuryl thioacetate using lipase from Candida rugosa produced 2-methyl-3-furanthiol and 2-furfurylthiol, respectively. When reactions were carried out at room temperature and pH 5.8, 2-methyl-3-furanthiol was produced in a optimal yield of 88% after 15 min of reaction, whereas 2-furfurylthiol was obtained in a yield of 80% after 1 h of reaction time. Enzymatic hydrolysis was also performed in n-hexane, n-pentane, and water/propylene glycol mixture. The reaction rates in these media were slower as compared to those in aqueous medium; however, the reaction yields were quite similar. As expected, the stability of the generated 2-methyl-3-furanthiol and 2-furfurylthiol was better in n-hexane, n-pentane, and the water/propylene glycol mixture as compared to that in water or phosphate buffer.  相似文献   

16.
Application of aroma extract dilution analysis using the volatile fraction of a Japanese green tea (Sen-cha) sample resulted in the detection of 36 odor-active peaks with flavor dilution (FD) factors between 10 and 5000. Thirty-six potent odorants were identified from 36 odor-active peaks by gas chromatography/mass spectrometry (GC/MS) and/or the multidimensional GC/MS (MDGC/MS) system. Among these components, 4-methoxy-2-methyl-2-butanethiol (meaty), (Z)-1, 5-octadien-3-one (metallic), 4-mercapto-4-methyl-2-pentanone (meaty), (E,E)-2,4-decadienal (fatty), beta-damascone (honey-like), beta-damascenone (honey-like), (Z)-methyl jasmonate (floral), and indole (animal-like) showed the highest FD factors. Therefore, these odorants were the most important components of the Japanese green tea odor. In addition, 4-methoxy-2-methyl-2-butanethiol, 4-mercapto-4-methyl-2-pentanone, methional, 2-ethyl-3, 5-dimethylpyrazine, (Z)-4-decenal, beta-damascone, maltol, 5-octanolide, 2-methoxy-4-vinylphenol, and 2-aminoacetophenone were newly identified compounds in the green tea.  相似文献   

17.
Differences in aroma components and total volatiles between a single unpasteurized Marsh grapefruit juice and its 65 Brix concentrate reconstituted to 10 Brix were examined using GC-olfactometry (GC-O) and GC-FID. Total volatiles (FID) in the reconstituted concentrate were reduced to less than 5% of initial values, but 57% of total aroma (GC-O) remained. Forty-one aroma-active compounds were observed in unpasteurized single strength juice, whereas 27 components were found in the unflavored reconstituted concentrate. Aroma-active compounds were classified into grapefruit/sulfury, sweet/fruity, fresh/citrusy, green/fatty/metallic, and cooked/meaty groups. Five of six components in the sweet/fruity and 14 of 18 green/fatty/metallic components survived thermal concentration. However, only 4-mercapto-4-methyl-2-pentanone in the grapefruit/sulfury group, and linalool and nootkatone from the fresh/citrusy group, were found in the reconstituted concentrate. Methional was the only aroma compound in the cooked/meaty category found in both juice types. beta-Damascenone and 1-p-menthen-8-thiol were found only in the reconstituted concentrate. 4-Mercapto-4-methyl-2-pentanol was found for the first time in grapefruit juice.  相似文献   

18.
Two kinds of pan-fired green teas (Japanese Kamairi-cha and Chinese Longing tea) were compared with the common Japanese green tea (Sen-cha). Application of the aroma extract dilution analysis (AEDA) using the volatile fraction of the Sen-cha, Kamairi-cha and Longing tea infusions revealed 32, 51, and 52 odor-active peaks with flavor dilution factors between 16 and 1024, respectively. (Z)-1,5-Octadien-3-one (metallic, geranium-like), 4-mercapto-4-methyl-2-pentanone (meaty, black currant-like), methional (potato-like), (E,Z)-2,6-nonadienal (cucumber-like), and 3-methylnonane-2,4-dione (green, fruity, hay-like) showed high flavor dilution factors in all varieties. In addition, 2-acetyl-1-pyrroline (popcorn-like), 2-ethyl-3,5-dimethylpyrazine (nutty), 2,3-diethyl-5-methylpyrazine (nutty), and 2-acetyl-2-thiazoline (popcorn-like) belonged to the most potent odorants only in the pan-fired green teas. Among these odorants, 2-acetyl-1-pyrroline and 2-acetyl-2-thiazoline were identified for the first time among the tea volatiles.  相似文献   

19.
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20.
Three types of yeast extract pastes from two different suppliers were compared. Compounds responsible for the key odors include 2-methyl-3-furanthiol, 2-methyl-3-methyldithiofuran, methional, 1-octen-3-one, dimethyltrisulphide together with a number of pyrazines, thiophenes, and aliphatic compounds. The three types of yeast extract paste differed in the intensity of their main odors and, in particular, those caused by furans, furanthiols, and heterocyclic sulfur compounds. Not only do pastes from different suppliers differ in terms of odor volatiles, but so do different treatments and batches of yeast extract from one supplier. The results suggest that normal variations in the concentrations of precursors and processing conditions may cause variations in the flavor of the end product.  相似文献   

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