OR2M3: A Highly Specific and Narrowly Tuned Human Odorant Receptor for the Sensitive Detection of Onion Key Food Odorant 3-Mercapto-2-methylpentan-1-ol.

The detection of key food odorants appears to be an important capability of odorant receptors. Here, thiols occupy an outstanding position among the 230 known key food odorants because of their very low odor thresholds. Members of the homologous series of 3-mercapto-2-methylalkan-1-ols have been described as onion key food odorants or food constituents and are detected at logarithmically different thresholds. 3-Mercapto-2-methylpentan-1-ol being the only key food odorant within this series also has the lowest odor threshold. Most odorants typically activate combinations of odorant receptors, which may be narrowly or broadly tuned. Consequently, a specific receptor activation pattern will define an odor quality. In contrast, here we show that just 1 of the 391 human odorant receptors, OR2M3, responded exclusively to 3-mercapto-2-methylpentan-1-ol of the 190 key food odorants tested, with a half maximal effective concentration at submicromolar concentration. Moreover, neither the Denisovan OR2M3 nor the closest OR2M3 homologs from five species did respond to this compound. This outstanding specificity of extremely narrowly tuned human OR2M3 can explain both odor qualities and odor threshold trend within a homologous series of 3-mercapto-2-methylalkan-1-ols and suggests a modern human-specific, food-related function of OR2M3 in detecting a single onion key food odorant.

Comprehensive two-dimensional gas chromatography and food sensory properties: potential and challenges.

Modern omics disciplines dealing with food flavor focus the analytical efforts on the elucidation of sensory-active compounds, including all possible stimuli of multimodal perception (aroma, taste, texture, etc.) by means of a comprehensive, integrated treatment of sample constituents, such as physicochemical properties, concentration in the matrix, and sensory properties (odor/taste quality, perception threshold). Such analyses require detailed profiling of known bioactive components as well as advanced fingerprinting techniques to catalog sample constituents comprehensively, quantitatively, and comparably across samples. Multidimensional analytical platforms support comprehensive investigations required for flavor analysis by combining information on analytes' identities, physicochemical behaviors (volatility, polarity, partition coefficient, and solubility), concentration, and odor quality. Unlike other omics, flavor metabolomics and sensomics include the final output of the biological phenomenon (i.e., sensory perceptions) as an additional analytical dimension, which is specifically and exclusively triggered by the chemicals analyzed. However, advanced omics platforms, which are multidimensional by definition, pose challenging issues not only in terms of coupling with detection systems and sample preparation, but also in terms of data elaboration and processing. The large number of variables collected during each analytical run provides a high level of information, but requires appropriate strategies to exploit fully this potential. This review focuses on advances in comprehensive two-dimensional gas chromatography and analytical platforms combining two-dimensional gas chromatography with olfactometry, chemometrics, and quantitative assays for food sensory analysis to assess the quality of a given product. We review instrumental advances and couplings, automation in sample preparation, data elaboration, and a selection of applications.

Nature's chemical signatures in human olfaction: a foodborne perspective for future biotechnology.

The biocatalytic production of flavor naturals that determine chemosensory percepts of foods and beverages is an ever challenging target for academic and industrial research. Advances in chemical trace analysis and post-genomic progress at the chemistry-biology interface revealed odor qualities of nature's chemosensory entities to be defined by odorant-induced olfactory receptor activity patterns. Beyond traditional views, this review and meta-analysis now shows characteristic ratios of only about 3 to 40 genuine key odorants for each food, from a group of about 230 out of circa 10 000 food volatiles. This suggests the foodborn stimulus space has co-evolved with, and roughly match our circa 400 olfactory receptors as best natural agonists. This perspective gives insight into nature's chemical signatures of smell, provides the chemical odor codes of more than 220 food samples, and beyond addresses industrial implications for producing recombinants that fully reconstruct the natural odor signatures for use in flavors and fragrances, fully immersive interactive virtual environments, or humanoid bioelectronic noses.

Formation of Key Aroma Compounds During 30 Weeks of Ripening in Gouda-Type Cheese Produced from Pasteurized and Raw Milk.

Gouda-type cheeses were produced on a pilot-scale from raw milk (RM-G) and pasteurized milk (PM-G). Sixteen key aroma compounds previously characterized by the sensomics approach were quantitated in the unripened cheeses and at five different ripening stages (4, 7, 11, 19, and 30 weeks) by means of stable isotope dilution assays. Different trends were observed in the formation of the key aroma compounds. Short-chain free fatty acids and ethyl butanoate as well as ethyl hexanoate continuously increased during ripening but to a greater extent in RM-G. Branched-chain fatty acids such as 3-methylbutanoic acid were also continuously formed and reached a 60-fold concentration after 30 weeks, in particular in PM-G. 3-Methylbutanal and butane-2,3-dione reached a maximum concentration after 7 weeks and decreased with longer ripening. Lactones were high in the unripened cheeses and increased only slightly during ripening. Recent results have shown that free amino acids were released during ripening. The aroma compounds 3-methylbutanal, 3-methyl-1-butanol, and 3-methylbutanoic acid are suggested to be formed by microbial enzymes degrading the amino acid l-leucine following the Ehrlich pathway. To gain insight into the quantitative formation of each of the three aroma compounds, the conversion of the labeled precursors (13C6)-l-leucine and (2H3)-2-keto-4-methylpentanoic acid into the isotopically labeled aroma compounds was studied. By applying the CAMOLA approach (defined mixture of labeled and unlabeled precursor), l-leucine was confirmed as the only precursor of the three aroma compounds in the cheese with the preferential formation of 3-methylbutanoic acid.

Influence of Milk Pasteurization on the Key Aroma Compounds in a 30 Weeks Ripened Pilot-Scale Gouda Cheese Elucidated by the Sensomics Approach.

Gouda cheese was produced from pasteurized milk and ripened for 30 weeks (PM-G). By application of gas chromatography/olfactometry and an aroma extract dilution analysis on the volatiles isolated by extraction/SAFE distillation, 25 odor-active compounds in the flavor dilution (FD) factor range from 16 to 4096 were identified. Butanoic acid, 2- and 3-methylbutanoic acid, and acetic acid showed the highest FD factors, and 2-phenylethanol, δ-decalactone, and δ-dodecalactone were most odor-active in the neutral-basic fraction. Quantitations by stable isotope dilution assays followed by a calculation of odor activity values (OAVs) revealed acetic acid, 3-methylbutanoic acid, butanoic acid, and butane-2,3-dione with the highest OAVs. Finally, an aroma recombinate prepared based on the quantitative data well agreed with the aroma profile of the PM-G. In Gouda cheese produced from raw (nonpasteurized) milk (RM-G), qualitatively the same set of odor-active compounds was identified. However, higher OAVs of butanoic acid, hexanoic acid, and their corresponding ethyl esters were found. On the other hand, in the PM-G, higher OAVs for 3-methylbutanoic acid, 3-methylbutanol, 3-methylbutanal, and butane-2,3-dione were determined. The different rankings of these key aroma compounds clearly reflect the aroma differences of the two Gouda-type cheeses. A higher activity of lipase in the RM-G and higher amounts of free l-leucine in PM-G on the other side were responsible for the differences in the concentrations of some key aroma compounds.

Changes in the Major Odorants of Grape Juice during Manufacturing of Dornfelder Red Wine.

Application of the aroma extract dilution analysis (AEDA) on a distillate prepared from freshly squeezed juice of Dornfelder grapes revealed (3Z)-hex-3-enal and trans-4,5-epoxy-(2E)-dec-2-enal with the highest flavor dilution (FD) factors. In contrast, in the final Dornfelder wine prepared thereof, the highest FD factors were found for 2-phenylethyl acetate, 2-phenylethan-1-ol, and (E)-ß-damascenone. However, for example, among others, (3Z)-hex-3-enal no longer appeared as an important odorant. To monitor the olfactory changes occurring in single processing steps from Dornfelder grapes to the final wine, selected odorants in grape juice, must, and young as well as aged wine from the same batch of Dornfelder grapes were quantitated. In particular, (3Z)-hex-3-enal and hexanal decreased considerably during mashing, while, as to be expected, the concentrations of yeast metabolites, e.g., odor-active alcohols and esters, drastically increased during fermentation. To reveal the influence of barrel aging, the odorants of the same Dornfelder wine aged in either barrique barrels or steel tanks were compared.

Characterization of the Key Aroma Compounds in a Freshly Prepared Oat (Avena sativa L.) Pastry by Application of the Sensomics Approach.

Oat flour has a weak cereal-like, powdery aroma, which is significantly changed by a thermal process. Application of an aroma extract dilution analysis on a distillate obtained from oat pastry prepared under defined conditions led to the detection of 43 odor-active areas in the flavor dilution (FD) factor range of 2-8192. Among them, 3-(methylthio)propanal (cooked-potato-like), 2-acetyl-1-pyrroline (roasty, popcorn-like), vanillin (vanilla-like), 2-methoxy-4-vinylphenol (clove-like), 1-octen-3-one (mushroom-like), 2-propionyl-1-pyrroline (roasty, popcorn-like), and (E,E,Z)-2,4,6-nonatrienal (oat-like) were identified with the highest FD factors. Nine aroma compounds were identified for the first time in oats or oat products, and (E,E,Z)-2,4,6-decatrienal, also showing an oat-like odor quality, is reported for the first time in foods. Quantitation of the 36 most important compounds by means of stable isotope dilution assays followed by a calculation of odor activity values on the basis of odor thresholds in corn starch revealed 2-acetyl-1-pyrroline, vanillin, the tautomers 2-acetyl-3,4,5,6-tetra-hydropyridine and 2-acetyl-1,4,5,6-tetrahydropyridine, 3-(methylthio)propanal, 2-propionyl-1-pyrroline, and methanethiol as the key aroma-active compounds. An aroma recombinate prepared in odorless oat pastry material containing 30 odorants in the concentrations determined in the oat pastry was able to successfully mimic the overall aroma profile of the original oat pastry.

Changes in the Concentrations of Key Aroma Compounds in Oat (Avena sativa) Flour during Manufacturing of Oat Pastry.

Application of the aroma extract dilution analysis on the volatiles isolated from oat flour revealed 30 aroma-active compounds in the flavor dilution (FD) factor range of 2-8192, among which oat-flour-like smelling (E,E,Z)-2,4,6-nonatrienal showed by far the highest FD factor. Quantitation performed by stable isotope dilution assays and a calculation of odor activity values (OAV; ratio of the concentration to odor threshold) of 23 odorants showed an OAV of above 1. Among them, vanillin, (E,E,Z)-2,4,6-nonatrienal, 2-acetyl-1-pyrroline, 3-methylbutanoic acid, and 2-methoxy-4-vinylphenol showed the highest OAVs. In a heated (70 °C for 30 min) oat dough prepared by kneading the oat flour in the presence of sucrose and water, 34 aroma-active compounds were identified, among which 17 compounds appeared with an OAV of ≥1. During frying, the weak cereal-like aroma of the oat flour and the oat dough was changed with the generation of an intense roasty, popcorn-like aroma attribute. A comparison to recently published data on oat pastry prepared by toasting of the same dough showed a clear increase in the overall aroma intensity from flour to pastry, in particular, in the popcorn-like, roasty odor impression. Especially considerable increases in the concentrations of the popcorn-like smelling compounds 2-acetyl-1-pyrroline, 2-acetyl-3,4,5,6- and 2-acetyl-1,4,5,6-tetrahydropyridine, 2-propionyl-1-pyrroline, and 2-acetyl-2-thiazoline were measured. In addition, the concentrations of the Strecker aldehydes 2- and 3-methylbutanal, phenylacetaldehyde, and 3-(methyldithio)propanal were also much increased during the toasting process. In contrast, in line with the overall aroma profile, particularly the concentration of the oat-like smelling compound (E,E,Z)-2,4,6-nonatrienal was decreased during processing. The formation and precursors of the key aroma compounds are discussed.

Characterization of the Key Aroma Compounds in a Commercial Fino and a Commercial Pedro Ximénez Sherry Wine by Application of the Sensomics Approach.

Following the sensomics approach, the key aroma compounds of a commercial Fino and Pedro Ximénez sherry were identified, quantitated, and validated through recombination experiments. In Fino sherry, 31 compounds were determined in concentrations above their odor detection thresholds, with the fruity/green smelling 1,1-diethoxyethane displaying the highest odor activity value ((OAV); the ratio of the concentration to the odor threshold) of 8970, followed by ethyl (2S,3S)-hydroxy-3-methylpentanoate (853) and 2- and 3-methylbutanal (448). In the Pedro Ximénez sherry, 23 compounds were present in concentrations exceeding their odor thresholds, and the malty smelling 2- and 3-methylbutanal were found with the highest OAV (1006), followed by 1,1-diethoxyethane (808) and methylpropanal (561). The results were compared to those characterized previously by us in an Amontillado sherry revealing that in all three sherry wines, 1,1-diethoxyethane, 2- and 3-methylbutanal, methylpropanal, ethanol, ethyl (2S,3S)-2-hydroxy-3-methylpentanoate, acetaldehyde, and 3-(methylthio)propanal, as well as the fruity-smelling ethyl 2-methylbutanoate, ethyl hexanoate, ethyl octanoate, and ethyl 3-methylbutanoate ranked among the 15 odorants with the highest OAVs. But, although most odorants were identical in the three sherries, their amounts differed significantly. The results are discussed considering the different winemaking processes and the different aroma profiles.

Characterization of the Key Aroma Compounds in Fresh Leaves of Garden Sage (Salvia officinalis L.) by Means of the Sensomics Approach: Influence of Drying and Storage and Comparison with Commercial Dried Sage.

The overall aroma profiles of commercial dried sage differ significantly from the profile of macerated fresh leaves. To clarify changes in the key aroma compounds, first an aroma extract dilution analysis was applied on an extract/distillate prepared from the fresh leaves of Italian garden sage cultivated in a green house in Germany. Among the 39 aroma active compounds characterized, (Z)-3-hexenal, 1,8-cineol, borneol and eugenol showed the highest flavor dilution (FD) factors. Odorants identified with FD factors between 64 and 8192 were quantitated to calculate odor activity values (OAV; ratio of concentration to odor threshold). The highest OAVs were determined for myrcene, (Z)-3-hexenal, (1S,2R,4S)-borneol and 1,8-cineol. A mixture of 22 key reference aroma compounds in the same concentrations as determined in the fresh sage leaves successfully mimicked the overall aroma profile of the spice. To get insight into changes induced by drying, all key aroma compounds were quantitated in sage leaves from the same plant by drying at 50 °C. While all monoterpenes remained nearly unchanged during drying, in particular highly volatile compounds such as dimethyl sulfide or 2- and 3-methylbutanal were decreased. Almost a total loss occurred for 3-(methylthio)propanal, phenylacetaldehyde, and (Z)-3-hexenal. By contrast, storage of the dried leaves for 12 months at room temperature in the dark did not much effect the concentrations of selected key odorants, thus indicating that drying is the most important factor for the changes in aroma compounds. Sensory profiling of six commercial sage samples showed different aroma profiles, which also clearly differed from the profile of the sage dried in lab scale, which was rated to elicit the most typical sage aroma. In addition, the concentrations of selected key aroma compounds as well as the total amount of volatiles were clearly lower in all commercial samples.

Characterization of the Key Odorants Causing the Musty and Fusty/Muddy Sediment Off-Flavors in Olive Oils.

Microbial spoilage of olive fruits is among the most frequent reasons for two types of off-flavors in olive oils, assigned as musty and fusty/muddy sediment. To characterize both off-flavors on a molecular level by means of the sensomics approach, the key aroma compounds in a premium extra virgin olive oil (PreOO1) eliciting the typical sensory properties were compared to those identified in two off-flavor olive oils obtained from the International Olive Council (IOC). A comparative aroma extract dilution analysis (cAEDA) followed by identification experiments revealed 53 odorants in the musty reference olive oil (MusOO1) and 48 odorants in the fusty/muddy sediment one (FusOO1). Odorants, differing in flavor dilution (FD) factors or showing a high FD factor in at least one of the olive oils, were quantitated by stable isotope dilution analysis (SIDA), followed by the calculation of odor activity values (OAVs; ratio of concentration of an odorant to the respective odor threshold in odorless refined sunflower oil). Aroma recombination and omission experiments revealed 13 key aroma compounds in MusOO1 and 12 in FusOO1. To demonstrate the importance of volatile phenols, 10 phenolic smelling odorants were quantitated in further 13 extra virgin olive oils, in 3 musty and in 13 fusty/muddy sediment defective olive oils, and in 8 olive oils with other off-flavors. Both sensory defects could successfully be discriminated from extra virgin olive oils by applying either a principal component analysis or a hierarchical cluster analysis. Considering possible reaction pathways and all results obtained including Pearson coefficients between the odorant concentrations and the intensities of the defects, specifically 2-methoxyphenol and 4-ethylphenol were proposed as marker compounds for the quality assignment of both types of off-flavors induced by microbial spoilage among the identified key aroma compounds.

Characterization of the Key Aroma Compounds in a Commercial Milk Chocolate by Application of the Sensomics Approach.

Compared to dark chocolate, which is mainly produced from roasted cocoa and sucrose, milk chocolates contain different dairy products, such as milk powder, butter fat, or dairy cream. This difference in recipe renders a typical aroma attributed to this type of chocolate, often described as milky or creamy. To get an idea of the odorants responsible for this odor note, an aroma extract dilution analysis was applied on a distillate obtained by extraction and SAFE distillation of a commercial milk chocolate evaluated with an intense "milky, creamy" attribute. The identification experiments in combination with the flavor dilution (FD) factors revealed 48 odor-active compounds, among which phenylacetic acid (honey-like) and vanillin (vanilla-like) showed the highest FD factors followed by 2-methoxyphenol (smoky) and nonanoic acid (musty, pungent). The quantitation of 40 odorants by stable isotope dilution assays (SIDA) and a subsequent calculation of odor activity values (OAV; ratio of concentration to odor threshold) revealed dimethyl trisulfide (cabbage-like) and butanoic acid (sweaty) with the highest OAVs (>170), followed by 3-methylbutanoic acid (sweaty), acetic acid (vinegar-like), and phenylacetic acid. An aroma recombinate prepared with 39 reference odorants in the same concentrations as those determined for the compounds in the milk chocolate showed a good similarity with the overall aroma profile of the milk chocolate. A comparison of the results with the recent literature data on dark chocolates also evaluated by the Sensomics approach suggested that, in particular, methanethiol and a series of lactones may contribute to the milky, creamy odor note because these were reported with much lower odor activities in the dark chocolates.

Quantitation of Key Aroma Compounds in Fresh, Raw Ginger (Zingiber officinale Roscoe) from China and Roasted Ginger by Stable Isotope Dilution Assays and Aroma Profiling by Recombination Experiments.

Twenty key odorants recently identified in raw and roasted ginger were quantitated by means of stable isotope dilution assays, of which six assays were newly developed. Odor activity values (OAV; ratio of concentration to odor threshold) revealed 1,8-cineol (eucalyptus-like) with by far the highest value of 65 000 followed by myrcene (geranium-like), for which an OAV of 19 000 was calculated. In addition, (R)-citronellal, geranial, (R)-linalool, (E)-isoeugenol, and (E)-2-octenal contributed with high OAVs to the overall aroma profile of the fresh, raw ginger. An aroma recombinate prepared with 20 reference compounds in the same concentrations as determined in the ginger sample successfully matched the overall aroma profile. In the roasted ginger, 1,8-cineol and myrcene remained the most odor-active compounds, however, the increase in some odorants, for example, in geraniol and (Z)-2-decenal, in combination with the newly formed caramel-like smelling 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel-like) and 3-(methylthio)propanal (potato-like) most likely caused the differences in the aroma profile initiated by the thermal treatment. A biomimetic aroma recombinate based on 21 aroma compounds was able to successfully simulate the aroma profile of the roasted ginger.

Comparison of the Key Aroma Compounds in Fresh, Raw Ginger (Zingiber officinale Roscoe) from China and Roasted Ginger by Application of Aroma Extract Dilution Analysis.

By application of a comparative aroma extract dilution analysis on the volatile fractions isolated by solvent extraction and solvent-assisted flavor evaporation (SAFE) from fresh raw Chinese ginger (Zingiber officinale Roscoe) and roasted ginger, 21 or 33 odorants, respectively, with flavor dilution (FD) factors in the range of 32-4096 were identified. In raw ginger, the highest FD factors were found for (E)-isoeugenol, 1,8-cineol, vanillin, geranial, and linalool. After roasting, in particular, the FD factors of 3-(methylthio)propanal (cooked potato-like), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel-like), 3-hydroxy-4,5-dimethyl-2(5H)-furanone (seasoning-like), and geraniol were substantially increased. The application of static headspace/olfactometry (SHO) on ground raw ginger revealed a high FD factor for highly volatile acetaldehyde which clearly decreased after roasting. By contrast, the SHO application revealed high FD factors for malty smelling methylpropanal and 3-methylbutanal, which both were exclusively detected in roasted ginger. Thirteen odorants, namely, decanoic acid, (Z)-2-decenal, (Z)-4-decenal, (E)-4,5-epoxy-(E)-2-decenal, (E)-4,5-epoxy-(E)-2-undecenal, fenchol, (Z)-3-hexenal, 3-hydroxy-4,5-dimethyl-2(5H)-furanone, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 3-methyl-2-buten-1-thiol, 2-methylpropanal, (E)-2-nonenal, and 1-nonen-3-one, were identified in ginger for the first time. Chiral analysis showed a much higher percent by weight portion for the (R)-enantiomer in citronellal, citronellol, and linalool, which was not much changed during pan-frying.

Changes in the Key Aroma Compounds of Raw Shiitake Mushrooms (Lentinula edodes) Induced by Pan-Frying As Well As by Rehydration of Dry Mushrooms.

Application of the aroma extract dilution analysis (AEDA) on an extract/distillate from raw shiitake mushrooms revealed 32 odorants among which 3-(methylthio)propanal (cooked potato), 1-octen-3-one, and 1-octen-3-ol (both mushroom-like) showed the highest flavor dilution (FD) factors. An isotope enrichment experiment with raw shiitake tissue and either 13C18-linoleic acid or 2H4-1-octen-3-ol confirmed that both 1-octen-3-ol and 1-octen-3-one are direct degradation products of the fatty acid, but it could be proven for the first time that the ketone is not formed by an oxidation of the alcohol. After pan-frying, 42 odor-active compounds appeared among which 3-hydroxy-4,5-dimethylfuran-2(5H)-one (savory), 1,2,4,5-tetrathiane (burnt, sulfury), 4-hydroxy-2,5-dimethylfuran-3(2H)-one (caramel-like), phenylacetic acid (honey-like), 3-(methylthio)-propanal, and trans-4,5-epoxy-(E)-2-decenal (metallic) showed the highest FD factors. To get a deeper insight into their aroma contribution, 19 key odorants were quantitated in the raw shiitake and twenty-one in the pan-fried mushrooms by stable isotope dilution assays, and new methods for the quantitation of four sulfur compounds were developed. A calculation of odor activity values (OAV; ratio of concentration to odor threshold) showed that 1-octen-3-one was by far the most important odorant in raw shiitake. During pan-frying, in particular, four aroma compounds were significantly increased, i.e., 4-hydroxy-2,5-dimethylfuran-3(2H)-one, dimethyl trisulfide, 1,2,4,5-tetrathiane, and 1,2,3,5,6-pentathiepane. The overall aroma profile of pan-fried shiitake could very well be mimicked by an aroma recombinate consisting of 15 reference aroma compounds in the concentrations determined in the pan-fried mushrooms. Further results showed that the sulfur compounds were even higher in rehydrated dry shiitake as compared to the pan-fried mushrooms.

Characterization of the Key Odorants in High-Quality Extra Virgin Olive Oils and Certified Off-Flavor Oils to Elucidate Aroma Compounds Causing a Rancid Off-Flavor.

To identify the odorants responsible for a rancid off-flavor in olive oils, first, the key aroma compounds in a premium extra virgin olive oil (PreOO1) were characterized by the sensomics approach and were then compared to those present in a certified rancid off-flavor olive oil (RanOO1) obtained from the International Olive Council (IOC). By application of an aroma extract dilution analysis, 46 odorants were detected and subsequently identified in PreOO1 and 35 odorants in RanOO1, respectively. After quantitation by stable isotope dilution assays, calculation of odor activity values (OAVs; ratio of concentration to odor threshold) revealed only 5 odorants with OAVs > 10 in PreOO1, while 13 odorants showed OAVs > 100 in RanOO1, with (E,Z)-2,4-decadienal, hexanoic acid, octanal, hexanal, (E)-2-octenal, and (Z)-2-nonenal being among the most odor-active compounds. Thus, marker aroma compounds for this off-flavor type could be suggested. Additionally, based on the OAVs obtained, the overall aroma profiles of both oils were mimicked by aroma recombination experiments. As proof of concept, 16 marker odorants were quantitated in two additional extra virgin olive oils and in eight further olive oils eliciting a rancid off-flavor. Application of a principal component analysis (PCA) and a hierarchical cluster analysis successfully discriminated both categories of olive oils. In the 12 olive oils used, acetic acid showed the highest Pearson coefficient between the perceived intensity of the rancid defect and the odorant concentration. In particular, (E,Z)- and (E,E)-2,4-decadienal and (Z)-2-nonenal can be suggested as chemical markers for olive oil rancidity in combination with positive aroma markers, for example, acetaldehyde and (Z)-3-hexenal.

Characterization of the Key Odorants in a High-Grade Chinese Green Tea Beverage (Camellia sinensis; Jingshan cha) by Means of the Sensomics Approach and Elucidation of Odorant Changes in Tea Leaves Caused by the Tea Manufacturing Process.

Sensory-guided analysis of the volatile fraction isolated from a freshly prepared green tea beverage (Camellia sinensis; type Jingshan cha) revealed 58 odor-active compounds after application of an aroma extract dilution analysis. Among them, 3-methylnonane-2,4-dione, (Z)-1,5-octadien-3-one, 3-(methylthio)propanal, trans-4,5-epoxy-(E)-2-decenal, methanethiol, dimethyl sulfide, and indole appeared with the highest flavor dilution factors. A quantitation of 42 aroma compounds by means of stable isotope dilution assays followed by the calculation of odor activity values (OAV; ratio of concentration to odor detection threshold) showed 27 key aroma compounds with OAVs ≥ 1. By far, the highest OAV of 458 was calculated for the asparagus-like/putrid smelling dimethyl sulfide followed by (E,E)-2,4-heptadienal (46). Finally, an aqueous recombinate containing all 27 aroma compounds in the concentrations measured in the beverage successfully mimicked the overall aroma profile of the tea infusion. Quantitative measurements were then performed on authentic tea material to elucidate changes in key aroma compounds during each processing step (fresh leaves, withering, pan-firing, rolling, and drying). The results indicated that dimethyl sulfide, one of the important aroma compounds, was significantly increased by withering of the fresh leaves, however, a major part was lost during drying. Linalool, geraniol, and hexanal showed the highest concentrations in the fresh tea leaves, while significantly lower concentrations were measured in the final tea. The same was observed for all lipid degradation products, such as (E,E)-2,4-heptadienal.

Screening for Novel Mercaptans in 26 Fruits and 20 Wines Using a Thiol-Selective Isolation Procedure in Combination with Three Detection Methods.

A selection of 46 fruits and wines were screened for mercaptans using a thiol-selective isolation procedure. The identification was based on three methods: gas chromatography-olfactometry (GC-O), gas chromatography-sulfur chemiluminescence detection (GC-SCD), and two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC-TOF/MS). A database constructed from analytical and sensory data for more than 300 sulfur compounds was used to confirm the identifications. Overall, 11 mercaptans were characterized in the fruits or wines for the first time. In addition, 1- p-menthene-9-thiol identified in kumquat is the first report in any food thus far. Thus, besides 1- p-menthene-8-thiol, p-menthane-8-thiole-3-one, and 3-mercapto-3,7-dimethyl-6-octenyl acetate, a fourth naturally occurring mercapto terpenoid occurs in fruits.

Characterization of the Key Aroma Compounds in Yeast Dumplings by Means of the Sensomics Concept.

The key odorants in the volatile fraction isolated from a steamed yeasted wheat dough (yeast dumpling) by solvent assisted flavor evaporation (SAFE) were characterized by an aroma extract dilution analysis (AEDA). The 29 aroma-active compounds were located within the flavor dilution (FD) factor range of 8-512. Among them, the highest FD factors were found for 2- and 3-methylbutanoic acid, 4-hydroxy-3-methoxybenzaldehyde, ( E, E)-2,4-decadienal, 2-phenylethanol, 4-hydroxy-2,5-dimethyl-3(2 H)-furanone, ( E)-2-nonenal, and butanoic acid. The 21 odorants were quantitated by stable isotope dilution assays (SIDA), and a subsequent calculation of odor activity values (OAV; ratio of concentration to odor threshold) revealed 3-methyl-1-butanol ( malty), 2-phenylethanol ( honey-like), trans-4,5-epoxy-( E)-2-decenal ( metallic), 2,3-butanedione ( buttery), 3-methylbutanoic acid ( sweaty), ( E)-2-nonenal ( cucumber-like), 1-octen-3-one ( mushroom-like), and 3-(methylthio)-propanal ( potato-like) as the most important contributors to the overall aroma of the dumpling. To verify the analytical results, a recombinate was prepared to show that a blend of the 21 aroma compounds in a buffered starch suspension resulted in a good replication of the overall yeast dumpling aroma.

Characterization of the Key Aroma Compounds in the Crust of Soft Pretzels by Application of the Sensomics Concept.

Soft pretzels show a uniform brown crust color and elicit a characteristic aroma that is clearly different from those of other small types of bread. Data on the odorants responsible for this unique aroma are scarcely available. Application of aroma extract dilution analysis (AEDA) on an extract (distillate) obtained from the crust of freshly baked soft pretzels followed by identification experiments revealed 4-hydroxy-2,5-dimethyl-3(2 H)-furanone (4-HDF, caramel-like) and 2-acetyl-1-pyrroline (2-ACPY; roasty, popcorn-like), which had the highest flavor dilution (FD) factors among the 28 odor-active compounds identified. Quantitation of all 28 aroma compounds by stable isotope dilution assays (SIDA) and calculation of odor activity values (OAV) confirmed 2-ACPY, 4-HDF, and phenylacetic acid as key contributors to the pretzel aroma profile. Compared with other pastry crusts, in particular, the low odor activities of the Strecker aldehydes 2- and 3-methylbutanal, the lipid degradation product ( E)-2-nonenal, and the lack of pyrazines were elucidated as the main reasons for the different aroma profile of pretzel crust. An aroma recombinate, which is among the first established for the crusts of breads and pastries, clearly mimicked the overall odor of the pretzel crust, in particular when a solution in ethanol was sprayed in the ambient air.