Determining Ultra-Low Organic Molecular Odor Thresholds in Air Helps Identify the Most Potent Fungal Aroma Compound.

The determination of odor threshold values can be performed in various matrices, including air, and serves as a parameter to compare the potencies of odorous compounds. Typically, the odor thresholds in air are determined by gas chromatography-olfactory (GC-O) and referenced to an internal standard, most often (E)-dec-2-enal. Herein, a direct gas chromatography-flame ionization detector-olfactory analysis method for the determination of odor thresholds in air is reported. As model substrates for this novel approach, naturally occurring substances (R)-1-p-menthene-8-thiol as well as (3S,3aS,6R,7aS)-3,6-dimethyl-3a,4,5,6,7,7a-hexahydro-3H-1-benzofuran-2-one were used. The latter compound was synthesized from (-)-isopulegol and exhibited an extremely low odor recognition threshold of 1.9 × 10-6 ng L-1 air, the lowest value reported for a fungal aroma compound thus far.

Fatty acids derived from oviposition systems guide female black soldier flies (Hermetia illucens) toward egg deposition sites.

The black soldier fly, Hermetia illucens, comes with big promises for industrial purposes since its larvae feed polyphagously on a broad spectrum of organic substrates. However, research focusing on adult flies is scarce, which is inconsistent with their reproductive relevance within the rearing cycle. In particular, directed oviposition is a challenge in artificial systems. Currently, decomposing organic matter is commonly used as oviposition substrate, which has extensive potential for improvement in view of the lack of standardization and the risk of microbial contamination. Here, we identified three fatty acids and one fatty acid methyl ester derived from the surface of old oviposition sites and targeted to elucidate their effect on preference behavior and oviposition site selection using Y-olfactometry and prepared oviposition sites, respectively. Exposure to tetradecanoic acid attracted gravid females and stimulated oviposition most strongly, while decanoic acid demonstrated a repulsive effect. Females kept in mixed-sex populations were attracted by tetradecanoic acid, resulting in a higher egg mass found in the compound box (3.0-11.4 fold), a ≥ 2.3 fold reduction of nonspecifically deposited eggs, and the highest total egg mass. Conversely, decanoic and dodecanoic acid caused females to lay a greater proportion of eggs nonspecifically outside both boxes. Our data suggest that fatty acids, especially tetradecanoic acid, are important cues for oviposition site selection in black soldier flies. In order to achieve a directed oviposition behavior, the role of further short- and long-chain fatty acids as attractants should be examined.

Biocatalytic Production of Odor-Active Fatty Aldehydes from Fungal Lipids.

Odor-active fatty aldehydes are important compounds for the flavor and fragrance industry. By a coupled enzymatic reaction using an α-dioxygenase (α-DOX) and an aldehyde dehydrogenase (FALDH), scarcely available aldehydes from the biotransformation of margaroleic acid [17:1(9Z)] were characterized and have shown highly interesting odor profiles, including citrus-like, soapy, herbaceous, and savory notes. In particular, (Z)-8-hexadecenal and (Z)-7-pentadecenal exhibited notable meaty odor characteristics. Submerged cultivation of Mortierella hyalina revealed the accumulation of the above-mentioned, naturally uncommon fatty acid 17:1(9Z). Its production was significantly increased by the modulation of culture conditions, whereas the highest accumulation was observed after 4 days at 24 °C and l-isoleucine supplementation. The lipase-, α-DOX-, and FALDH-mediated biotransformation of M. hyalina lipid extract resulted in a complex aldehyde mixture with a high aldehyde yield of ∼50%. The odor qualities of the formed aldehydes were assessed by means of gas chromatography-olfactometry, and several of the obtained fatty aldehydes have been sensorially described for the first time. To assess the aldehyde mixture's potential as a flavor ingredient, a sensory evaluation was conducted. The obtained product exhibited intense citrus-like, green, and soapy odor impressions.

Formation of a Meat-Like Flavor by Submerged Cultivated Laetiporus montanus.

Basidiomycota are natural sources of aroma compounds. When grown in submerged cultures, the fungus Laetiporus montanus (LMO) forms a spicy and meat-like aroma. It thus represents an interesting candidate for the production of natural savory flavors. To identify the key aroma compounds of LMO grown submerged in malt extract peptone medium, the volatiles were isolated by means of automated solvent assisted flavor evaporation (aSAFE). An aroma extract dilution analysis was performed by means of gas chromatography-olfactometry coupled with a flame ionization detector (GC-FID-O). In the aSAFE extract of LMO, 24 aroma-active compounds were detected. 5-Butyl-2(5H)-furanone (FD 4096), perceived as coconut-like, was determined as the compound with the highest FD factor. (E,E)-2,4-Decadienal, (E,Z)-2,4-decadienal, and sotolon were identified as responsible key compounds for the spicy odor of the submerged cultures. Moreover, supplementation of the cultures of LMO, Laetiporus sulphureus, and Laetiporus persicinus with 13C-labeled thiamine hydrochloride resulted in the formation of 2-methyl-3-(methylthio)furan (MMTF), a compound with a pronounced meaty flavor. The concentrations of MMTF were further increased to 19-27 µg L-1 by additional supplementation of the cultures with ascorbic acid. The results of this study indicate potential for the biotechnological production of a meat-like flavor by Laetiporus species.

Structure Elucidation of Aroma-Active Bicyclic Benzofuran Derivatives Formed by Cystostereum murrayi.

Among the monoterpenoid aroma compounds formed by the basidiomycete Cystostereum murrayi are highly potent bicyclic benzofuran derivatives. In addition to the dill ethers previously described in a few fungi, two stereoisomers of the rare 3,6-dimethyl-3a,4,5,6,7,7a-hexahydro-3H-1-benzofuran-2-one (1a and 2c), also known as dihydromenthofurolactones, and a C3-unsaturated analogue (3a) are formed by C. murrayi. The analysis of synthesized reference standards of the lactones allowed an unambiguous assignment of the stereoisomers formed by the fungus. Despite a similar structure, two key differences in the stereochemistry of the lactones and dill ethers emerged. The analysis of submerged cultures further revealed the formation of additional, so far unknown, fungal terpenoids, including limonen-10-ol (7) and the corresponding aldehyde limonen-10-al (8). Analysis of chiral terpenoids as well as supplementation studies, including stable isotope-labeled compounds, indicated independent biogenesis pathways for dill ethers and lactones.

Upcycling of black currant pomace for the production of a fermented beverage with Wolfiporia cocos.

Pomace as a side stream from black currant juice production is mostly discarded, even though it is rich in nutrients like protein, fiber, sugars, anthocyanins, polyphenols, and other secondary metabolites. Fungi from the division of Basidiomycota have a great enzymatic toolbox to recycle these complex mixtures of nutrients. In particular, the edible medicinal fungus Wolfiporia cocos has been described as a suitable biocatalyst to form pleasant aroma compounds in fermentation processes. Therefore, medium optimization, upscaling, and filtration were performed to produce a beverage based on black currant pomace fermented with W. cocos. A trained panel described the beverage as highly pleasant, reminiscent of honey, flowers and berries with a well-balanced sour and sweet taste. The flavor compounds linalool (citrus), geraniol (flowery), phenylacetic acid (honey), methyl phenylacetate (honey), eugenol (clove), and 2-phenylethanol (rose) were produced during fermentation and the concentrations exceeded their respective odor thresholds. The produced beverage was evaluated with 8.0 ± 1.4 from 10 for the question of whether panelists would buy the product. Fungal fermentation with the edible fungus W. cocos enabled the production of a highly pleasant beverage and additionally may reduce waste by using pomace and table sugar as sole ingredients. Supplementary Information: The online version contains supplementary material available at 10.1007/s13197-023-05677-4.

An enzymatic tandem reaction to produce odor-active fatty aldehydes.

Aldehydes represent a versatile and favored class of flavoring substances. A biocatalytic access to odor-active aldehydes was developed by conversion of fatty acids with two enzymes of the α-dioxygenase pathway. The recombinant enzymes α-dioxygenase (α-DOX) originating from Crocosphaera subtropica and fatty aldehyde dehydrogenase (FALDH) from Vibrio harveyi were heterologously expressed in E. coli, purified, and applied in a coupled (tandem) repetitive reaction. The concept was optimized in terms of number of reaction cycles and production yields. Up to five cycles and aldehyde yields of up to 26% were achieved. Afterward, the approach was applied to sea buckthorn pulp oil as raw material for the enzyme catalyzed production of flavoring/fragrance ingredients based on complex aldehyde mixtures. The most abundant fatty acids in sea buckthorn pulp oil, namely palmitic, palmitoleic, oleic, and linoleic acid, were used as substrates for further biotransformation experiments. Various aldehydes were identified, semi-quantified, and sensorially characterized by means of headspace-solid phase microextraction-gas chromatography-mass spectrometry-olfactometry (HS-SPME-GC-MS-O). Structural validation of unsaturated aldehydes in terms of double-bond positions was performed by multidimensional high-resolution mass spectrometry experiments of their Paternò-Büchi (PB) photoproducts. Retention indices and odor impressions of inter alia (Z,Z)-5,8-tetradecadienal (Z,Z)-6,9-pentadecadienal, (Z)-8-pentadecenal, (Z)-4-tridecenal, (Z)-6-pentadecenal, and (Z)-8-heptadecenal were determined for the first time. KEY POINTS: • Coupled reaction of Csα-DOX and VhFALDH yields chain-shortened fatty aldehydes. • Odors of several Z-unsaturated fatty aldehydes are described for the first time. • Potential for industrial production of aldehyde-based odorants from natural sources.

Generation of Flavor-Active Compounds by Electrochemical Oxidation of (R)-Limonene.

Terpenes may be converted by electrochemical oxidation to various oxidized products with appealing aroma properties. In this study, (R)-limonene was anodically oxidized in the presence of ethanol, and the resulting mixture exhibited a pleasing fruity, herbal, citrus-like, and resinous odor. The aroma-active compounds were purified by means of preparative high-performance liquid chromatography, and their structures were elucidated by means of gas chromatography (GC)-mass spectrometry and nuclear magnetic resonance spectroscopy. In addition, the odor of the isolated compounds was determined by means of GC-olfactometry. Seventeen compounds were isolated, and for only four of them, analytical data had been reported previously in the literature. Furthermore, only for two of the compounds, an odor description had been available in the literature.

Odor Characteristics of Novel Non-Canonical Terpenes.

Several non-canonical, methylated terpenes have been described as products of genetically modified Escherichia coli recently, and the aroma properties of 28 odor-active methylated derivatives of prenol, isoprenol, bornane, camphene, carene, citronellol, fenchol, geraniol, limonene, linalool, terpineol, and farnesol were characterized for the first time in the current study. Twelve methylated monoterpenes exhibited a particularly intense and pleasant odor and were therefore chosen for the determination of their respective odor thresholds (OTs) in comparison to their non-methylated equivalents. In addition to the determination of OTs based on the literature value for the internal standard, (2E)-decenal, the threshold values of the compounds with individually determined OTs of the participants were calculated. This enabled a more precise identification of the OTs. Among the non-canonical terpenes, the lowest OTs in the air were found for 2-methyllinalool (flowery, 1.8 ng L-1), 2-methyl-α-fenchol (moldy, 3.6 ng L-1), 2-methylgeraniol (flowery, 5.4 ng L-1), 2-methylcitronellol (citrus-like, 7.2 ng L-1), and 4-methylgeraniol (citrus-like, 16 ng L-1). The derivatives of geraniol, linalool, and citronellol showed very pleasant odor impressions, which could make them interesting for use as flavoring agents in the flavor and fragrance industry.

Production of an Anise- and Woodruff-like Aroma by Monokaryotic Strains of Pleurotus sapidus Grown on Citrus Side Streams.

The production of natural flavors by means of microorganisms is of great interest for the food and flavor industry, and by-products of the agro-industry are particularly suitable as substrates. In the present study, Citrus side streams were fermented using monokaryotic strains of the fungus Pleurotus sapidus. Some of the cultures exhibited a pleasant smell, reminiscent of woodruff and anise, as well as herbaceous notes. To evaluate the composition of the overall aroma, liquid/liquid extracts of submerged cultures of a selected monokaryon were prepared, and the volatiles were isolated via solvent-assisted flavor evaporation. Aroma extract dilution analyses revealed p-anisaldehyde (sweetish, anisic- and woodruff-like) with a flavor dilution factor of 218 as a character impact compound. The coconut-like, herbaceous, and sweetish smelling acyloin identified as (2S)-hydroxy-1-(4-methoxyphenyl)-1-propanone also contributed to the overall aroma and was described as an aroma-active substance with an odor threshold in air of 0.2 ng L-1 to 2.4 ng L-1 for the first time. Supplementation of the culture medium with isotopically substituted l-tyrosine elucidated this phenolic amino acid as precursor of p-anisaldehyde as well as of (2S)-hydroxy-1-(4-methoxyphenyl)-1-propanone. Chiral analysis via HPLC revealed an enantiomeric excess of 97% for the isolated product produced by P. sapidus.

Wild Strawberry-like Flavor Produced by the Fungus Wolfiporia cocos─Identification of Character Impact Compounds by Aroma Dilution Analysis after Dynamic Headspace Extraction.

Brown-rot fungi are particularly suitable for the sustainable and cost-efficient biotechnological production of natural flavors. In this study, Wolfiporia cocos was employed for the fermentation of European black currant pomace supplemented with aspartate in surface cultures to produce a flavor reminiscent of wild strawberries. Aroma dilution analysis (ADA) by means of dynamic headspace extraction was developed as a suitable technique for solid samples. The character impact compounds were quantified by stable isotope dilution analysis and standard addition and validated by recombination experiments. (R)-Linalool (1879 µg kg-1, ADA 211), methyl anthranilate (2206 µg kg-1, 210), 2-aminobenzaldehyde (771 µg kg-1, 25), and geraniol (138 µg kg-1, 25) were identified as key aroma compounds. Recombination experiments demonstrated that the combination of the four analyzed compounds was responsible for the odor impression reminiscent of wild strawberries.

Formation of Diastereomeric Dihydromenthofurolactones by Cystostereum murrayi and Aroma Dilution Analysis Based on Dynamic Headspace Extraction.

Submerged cultures of the basidiomycota Cystostereum murrayi emit an intensive coconut-like, sweetish, and buttery smell. For identification of the key aroma compounds, an aroma dilution analysis using dynamic headspace was performed by adjusting the split ratio of the GC inlet system. Flavor dilution (FD) factors varied from 22 up to ≥218, whereby the largest class of compounds represented terpenoids, including two rare stereoisomers of 3,6-dimethyl-2,3,3a,4,5,7a-hexahydrobenzofuran (dill ether, ee ≥ 99.9). By means of nuclear magnetic resonance spectroscopy, the substances with the highest FD factors (29, 212, and 218) were identified as diastereomers of 3,6-dimethyl-3a,4,5,6,7,7a-hexayhydro-3H-1-benzofuran-2-one (dihydromenthofurolactone) and as its corresponding C3-unsaturated lactone. The latter two compounds have not been described for Cystostereum murrayi or for any other basidiomycota previously. Supplementation studies using 2-13C-d-glucose indicated that these lactones as well as the two stereoisomers of dill ether and other terpenoids were formed de novo by the fungus.

Biotechnological Production and Sensory Evaluation of ω1-Unsaturated Aldehydes.

Lipid extracts of the fungus Flammulina velutipes were found to contain various scarce fatty acids including dodec-11-enoic acid and di- and tri-unsaturated C16 isomers. A biotechnological approach using a heterologously expressed carboxylic acid reductase was developed to transform the fatty acids into the respective aldehydes, yielding inter alia dodec-11-enal. Supplementation studies gave insights into the fungal biosynthesis of this rarely occurring acid and suggested a terminal desaturation of lauric acid being responsible for its formation. A systematic structure-odor relationship assessment of terminally unsaturated aldehydes (C7-C13) revealed odor thresholds in the range of 0.24-22 µg/L in aqueous solution and 0.039-29 ng/L in air. In both cases, non-8-enal was identified as the most potent compound. All aldehydes exhibited green odor qualities. Short-chained substances were additionally associated with grassy, melon-, and cucumber-like notes, while longer-chained homologs smelled soapy and coriander leaf-like with partly herbaceous nuances. Dodec-11-enal turned out to be of highly pleasant scent without off-notes.

Branched-Chain Fatty Acids as Mediators of the Activation of Hepatic Peroxisome Proliferator-Activated Receptor Alpha by a Fungal Lipid Extract.

The study aimed to test the hypothesis that monomethyl branched-chain fatty acids (BCFAs) and a lipid extract of Conidiobolus heterosporus (CHLE), rich in monomethyl BCFAs, are able to activate the nuclear transcription factor peroxisome proliferator-activated receptor alpha (PPARalpha). Rat Fao cells were incubated with the monomethyl BCFAs 12-methyltridecanoic acid (MTriA), 12-methyltetradecanoic acid (MTA), isopalmitic acid (IPA) and 14-methylhexadecanoic acid (MHD), and the direct activation of PPARalpha was evaluated by reporter gene assay using a PPARalpha responsive reporter gene. Furthermore, Fao cells were incubated with different concentrations of the CHLE and PPARalpha activation was also evaluated by using the reporter gene assay, and by determining the mRNA concentrations of selected PPARalpha target genes by real-time RT-PCR. The reporter gene assay revealed that IPA and the CHLE, but not MTriA, MHD and MTA, activate the PPARalpha responsive reporter gene. CHLE dose-dependently increased mRNA concentrations of the PPARalpha target genes acyl-CoA oxidase (ACOX1), cytochrome P450 4A1 (CYP4A1), carnitine palmitoyltransferase 1A (CPT1A) and solute carrier family 22 (organic cation/carnitine transporter), member 5 (SLC22A5). In conclusion, the monomethyl BCFA IPA is a potent PPARalpha activator. CHLE activates PPARalpha-dependent gene expression in Fao cells, an effect that is possibly mediated by IPA.

Biotechnological Production of Odor-Active Methyl-Branched Aldehydes by a Novel α-Dioxygenase from Crocosphaera subtropica.

As a result of their pleasant odor qualities and low odor thresholds, iso- and anteiso-fatty aldehydes represent promising candidates for applications in flavoring preparations. A novel cyanobacterial α-dioxygenase from Crocosphaera subtropica was heterologously expressed in Escherichia coli and applied for the biotechnological production of C12-C15 branched-chain fatty aldehydes. The enzyme has a sequence identity of less than 40% to well-investigated α-dioxygenase from rice. Contrary to the latter, it efficiently transformed short-chained fatty acids. The kinetic parameters of α-dioxygenase toward unbranched and iso-branched-chain substrates were studied by means of an oxygen-depletion assay. The transformation products (C12-C15 iso- and anteiso-aldehydes) were extensively characterized, including their sensory properties. The aldehydes exhibited green-soapy, sweety odors with partial citrus-like, metallic, peppery, and savory-tallowy nuances. Moreover, the two C14 isomers showed particularly low odor threshold values of 0.2 and 0.3 ng/L in air as determined by means of gas chromatography-olfactometry.

Industrial Riboflavin Fermentation Broths Represent a Diverse Source of Natural Saturated and Unsaturated Lactones.

Fermentation broths of Ashbya gossypii from the industrial production of riboflavin emit an intense floral, fruity, and nutty smell. Typical Ehrlich pathway products, such as 2-phenylethan-1-ol and 2-/3-methylbutan-1-ol, were detected in large amounts as well as some intensely smelling saturated and unsaturated lactones, e.g., γ-decalactone and γ-(Z)-dodec-6-enlactone. An aroma extract dilution analysis identified 2-phenylethan-1-ol and γ-(Z)-dodec-6-enlactone as the main contributors to the overall aroma, with flavor dilution factors of 32 768. The position of the double bonds of unsaturated lactones was determined by the Paternò-Büchi reaction, and reference compounds that were not available commercially were synthesized to elucidate the structures of the uncommon lactones. The absolute configuration and enantiomeric excess values of the lactones were determined by converting the lactones to their corresponding Mosher's esters. In addition, the odor impressions and odor thresholds in air were determined.

Aroma characterization of a wild plant (Sanguisorba albanica) from Kosovo using multiple headspace solid phase microextraction combined with gas chromatography-mass spectrometry-olfactometry.

A wild plant (Sanguisorba albanica) from Kosovo exhibits an appealing aroma, which was perceived as intensely fresh, green, and slightly sweetish with hints of cucumber, melon, and green tea. The characteristic aroma of S. albanica was analyzed for the first time by employing advanced molecular sensory techniques coupled with multiple headspace solid phase microextraction (MHS-SPME). Thirty-six different odor impressions were perceived, and 34 corresponding compounds were identified by a gas chromatography system equipped with a mass spectrometric detector and an olfactory detection port. By aroma dilution analysis, sixteen key odorants with flavor dilution factors higher than 16 were identified. Their respective concentrations were quantified by means of MHS-SPME according to the determined ß values (0.43-0.83), and odor activity values (OAVs) were calculated. (E,Z)-2,6-Nonadienal (green, melon-like, and sweetish odor; OAV 20,046), followed by linalool (floral and citrus-like odor; OAV 10,563), (Z)-6-nonenal (cucumber-like, green, and melon-like odor; OAV 4200), ethyl isobutyrate (floral and fruity odor; OAV 1315), and (E)-2-nonenal (green and fatty odor; OAV 1062) were representative odorants contributing to the overall aroma of S. albanica. Differences between stems, leaves, and flowers of S. albanica with regard to the key odorants were also presented. Intensely green and floral aromas of the leaves and flowers were greatly attributed to (E,Z)-2,6-nonadienal and linalool, respectively. Apart from these compounds, (Z)-6-nonenal contributed to the overall aroma of the stems as well.

Aroma Investigation of Chios Mastic Gum (Pistacia lentiscus Variety Chia) Using Headspace Gas Chromatography Combined with Olfactory Detection and Chiral Analysis.

Chios mastic gum (Pistacia lentiscus var. Chia) exhibits intensely sourish, green, resinous, and woody odor notes with hints of citrus and pine. Despite its attractive flavor, no description of its aroma properties by molecular sensory techniques has been published thus far. A total of 25 odor-active compounds with flavor dilution (FD) factors of 1-512 were identified by gas chromatography-mass spectrometry-olfactometry (GC-MS-O) combined with headspace solid-phase microextraction (HS-SPME) and stir bar sorptive extraction (HS-SBSE). Quantitative analyses performed by multiple HS-SPME and calculation of odor activity values of 10 odorants with high FD factors revealed an essential role of several minor components (e.g., ß-myrcene, limonene, ß-linalool, and perillene) for the overall aroma of mastic gum, besides the dominating compound α-pinene. The indispensable contribution of the minor odorants to mastic gum was further confirmed by aroma recombination and omission tests. Varying enantiomeric excess values of the key odorants were observed by multidimensional GC-MS.

Aroma Profile Analyses of Filamentous Fungi Cultivated on Solid Substrates.

Filamentous fungi have been used since centuries in the production of food by means of solid substrate fermentation (SSF). The most applied SSF involving fungi is the cultivation of mushrooms, e.g., on tree stumps or sawdust, for human consumption. However, filamentous fungi are also key players during manufacturing of several processed foods, like mold cheese, tempeh, soy sauce, and sake. In addition to their nutritive values, these foods are widely consumed due to their pleasant flavors. Based on the potentials of filamentous fungi to grow on solid substrates and to produce valuable aroma compounds, in recent decades, several studies concentrated on the production of aroma compounds with SSF, turning cheap agricultural wastes into valuable flavors. In this review, we focus on the presentation of common analytical methods for volatile substances and highlight various applications of SSF of filamentous fungi dealing with the production of aroma compounds. Graphical Abstract.

Biosynthesis of Stereoisomers of Dill Ether and Wine Lactone by Pleurotus sapidus.

The white-rot fungus Pleurotus sapidus (PSA) biosynthesizes the bicyclic monoterpenoids 3,6-dimethyl-2,3,3a,4,5,7a-hexahydrobenzofuran (dill ether) (1) and 3,6-dimethyl-3a,4,5,7a-tetrahydro-1-benzofuran-2(3H)-one (wine lactone) (2). Submerged cultures grown in different media were analyzed by gas chromatography-mass spectrometry. The stereochemistry of the formed isomers was elucidated by comparing their retention indices to those of reference compounds by enantioselective multidimensional gas chromatography. The basidiomycete produced the rare (3R,3aR,7aS) and (3S,3aR,7aS) stereoisomers of dill ether and wine lactone. Kinetic analyses of the volatilome and bioprocess parameters revealed that the biosynthesis of the bicyclic monoterpenoids correlated with the availability of the primary carbon source glucose. Spiking the media with 13C-labeled glucose demonstrated that the compounds were produced de novo. Supplementation studies i.a. with isotopically labeled substrates further identified limonene and p-menth-1-en-9-ol as intermediate compounds in the fungal pathways. PSA was able to biotransform all enantiomeric forms of the latter compounds to the respective isomers of dill ether and wine lactone.