Synthesis of deuterated volatile lipid degradation products to be used as internal standards in isotope dilution assays. 2. Vinyl ketones

First identification of a new molecule involved in the fresh mushroom off-flavor in wines: 1-hydroxyoctan-3-one

The fresh mushrooms off-flavor (FMOff) has been appearing in wines since the 2000 s; the C8 compounds, 1-octen-3-one, 1-octen-3-ol and 3-octanol are involved in this specific taint, yet they alone do not fully explain its occurrence. The objective of this work was to identify by GC-MS new FMOff markers in contaminated matrices, to correlate compound levels with wine sensory characterization and to determine the sensory attributes of 1-hydroxyoctan-3-one, a new candidate involved in FMOff. In practice, grape musts were artificially contaminated with Crustomyces subabruptus, and fermented to obtain tainted wines. GC-MS analysis of contaminated musts and wines revealed the presence of 1-hydroxyoctan-3-one only in contaminated musts, and not in the healthy control. In a selection of 16 wines affected by FMOff, the level of 1-hydroxyoctan-3-one correlated significantly (r² = 0.86) with sensory analysis scores. Finally, 1-hydroxyoctan-3-one was synthesized and found to generate a fresh mushroom aroma in a wine matrix.

Toward High-Throughput Analysis of Aroma Compounds Using Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry: Screening of Key Food Odorants in Various Foods

Recent studies show the immense capacities of the unified quantitation of aroma and taste compounds using liquid chromatography-mass spectrometry (LC-MS). The goal of this study was to highlight the broad application of this unified method. Thus, a stable isotope dilution analysis quantification method of the most important key food odorants in various food categories by LC-MS was developed. Using the well-known derivatization agent 3-nitrophenylhydrazine for carbonyl derivatization and a newly developed approach for alcohol and thiol derivatization, a method for the quantitation of 20 key food odorants was established. Intraday precision was determined to be ≤26%, and interday precision was between 24 and 31%. Limits of quantitation were determined between 0.014 and 283 μg/kg. The work shows that a wide array of aroma compounds can be analyzed accurately by LC-MS.

Key Odorants of Raw and Cooked Green Kohlrabi (Brassica oleracea var. gongylodes L.)

Volatile compounds of raw and cooked green kohlrabi were investigated using a sensomics approach. A total of 55 odor-active compounds were detected and identified in raw and cooked green kohlrabi using GC-O. Twenty-eight odor-active compounds with high flavor dilution (FD) factors ranging from 64 to 1024 were quantitated, and odor activity values (OAVs) were determined. Eight compounds showed high OAVs in raw and cooked kohlrabi: five sulfur compounds (dimethyl trisulfide, methyl 2-methyl-3-furyl disulfide, and three isothiocyanates (1-isothiocyanato-3-(methylsulfanyl)propane, benzyl isothiocyanate, and 1-isothiocyanato-4-(methylsulfanyl)butane)), two lipid oxidation products (1-octen-3-one and trans-4,5-epoxy-(2E)-dec-2-enal), and 2-isopropyl-3-methoxypyrazine. Among these, the sulfur compounds contributed most to the overall smell of the raw and cooked vegetables. The quantitation analysis indicates that the eight odorants are the backbone compounds for raw and cooked kohlrabi. The OAVs for the backbone compounds and also for minor odorants are clearly higher in raw kohlrabi than in the cooked one. Differences can be explained by the influence of the cooking process.

Identification of Characterizing Aroma Components of Roasted Chicory "Coffee" Brews

The roasted and ground root of the chicory plant (Cichorium intybus), often referred to as chicory coffee, has served as a coffee surrogate for well over 2 centuries and is still in common use today. Volatile components of roasted chicory brews were identified by direct solvent extraction and solvent-assisted flavor evaporation (SAFE) combined with gas chromatography-olfactometry (GC-O), aroma extract dilution analysis (AEDA), and gas chromatography-mass spectrometry (GC-MS). A total of 46 compounds were quantitated by stable isotope dilution analysis (SIDA) and internal standard methods, and odor-activity values (OAVs) were calculated. On the basis of the combined results of AEDA and OAVs, rotundone was considered to be the most potent odorant in roasted chicory. On the basis of their high OAVs, additional predominant odorants included 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon), 2-methylpropanal, 3-methylbutanal, 2,3-dihydro-5-hydroxy-6-methyl-4H-pyran-4-one (dihydromaltol), 1-octen-3-one, 2-ethyl-3,5-dimethylpyrazine, 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF), and 3-hydroxy-2-methyl-4-pyrone (maltol). Rotundone, with its distinctive aromatic woody, peppery, and "chicory-like" note was also detected in five different commercial ground roasted chicory products. The compound is believed to an important, distinguishing, and characterizing odorant in roasted chicory aroma. Collectively, a group of caramel- and sweet-smelling odorants, including dihydromaltol, cyclotene, maltol, HDMF, and sotolon, are also thought to be important aroma contributors to roasted chicory aroma.

Quantitative Analyses of Key Odorants and Their Precursors Reveal Differences in the Aroma of Gluten-Free Rice Bread and Wheat Bread

Rice flour is one of the most important raw materials in gluten-free products. However, the aroma of gluten-free rice bread is less accepted by consumers than that of commercial wheat bread. Therefore, 18 selected aroma compounds were determined in rice and wheat breads by stable isotope dilution assays (SIDA) to elucidate differences in the sensory characteristics, concentrations, and odor activity values (OAVs). The OAVs of most aroma compounds varied greatly between a rice and a wheat bread. In particular, 2-aminoacetophenone with a grape-like, medicinal aroma was characteristic for rice bread crumb and crust, while maltol was only relevant in wheat bread crust. Ehrlich pathway products varied in their concentration between the bread crumbs and were correlated with the contents of their corresponding free amino acid precursors in the flours and doughs. The analysis of rice flour revealed that only a few aroma compounds were retained in the bread. Consequently, the bread making process has a high relevance in aroma compound formation. In a comparison of breads prepared from fresh and stored rice flour, hexanal was identified as an important indicator for aging in rice bread and flour.

Characterization of the Key Aroma Compounds in Heat-Processed Licorice (Succus Liquiritiae) by Means of Molecular Sensory Science

Application of the sensomics concept elucidated the key odorants of heat-processed licorice (Succus Liquiritiae). Forty-nine aroma-active compounds with flavor dilution (FD) factors between 16 and 2048 were detected; 47 thereof were identified, 23 for the first time in heated licorice. 4-Hydroxy-2,5-dimethylfuran-3(2H)-one revealed the highest FD factor of 2048, followed by 3-hydroxy-4,5-dimethylfuran-2(5H)-one, 4-hydroxy-3-methoxybenzaldehyde, 3-hydroxy-2-methyl-4H-pyran-4-one, and 2-methoxyphenol (all 1024). Forty-two substances were quantitated by stable isotope dilution assays (SIDAs), and odor activity values (OAVs; ratio of concentration to the respective odor threshold) were calculated revealing OAVs ≥ 1 for 29 compounds. Thereby, 3-hydroxy-4,5-dimethylfuran-2(5H)-one, 2,3-butanedione, 2-methoxyphenol, and 1,8-cineole showed the highest OAVs in Succus Liquiritiae. To validate the obtained data, a reconstitution model based on an aqueous sucrose solution (50%) was prepared, containing all 29 odorants with an OAV ≥ 1 in their naturally occurring concentrations. The recombinate elicited an aroma profile matching very well with the profile of the original heat-processed licorice, proving the correct identification and quantitation of all key aroma compounds of Succus Liquiritiae.

Aroma-Active Compounds in Bartlett Pears and Their Changes during the Manufacturing Process of Bartlett Pear Brandy

Application of aroma extract dilution analysis to Bartlett pears and the fermented mash produced thereof revealed 24 and 34 aroma-active compounds in the flavor dilution (FD) factor range between 8 and 8192. Twenty-eight compounds, which have not been described before in Bartlett pears or in fermented pear mash, were identified. While ethyl (E,Z)-2,4-decadienoate (pear-like, metallic odor impression), hexyl acetate (green, fruity), and acetic acid (vinegar-like) showed the highest concentrations in Bartlett pears, ethanol (ethanolic), acetic acid, 3-methyl-1-butanol (malty), 1-hexanol (grassy, marzipan-like), (S)-2- and 3-methylbutanoic acid (sweaty), and 2-phenylethanol (flowery, honey-like) were present at the highest amounts in the fermented mash. The key aroma compounds were quantitated in each pear brandy production step (pears, fermented mash, distillate, and aged distillate) by stable isotope dilution analysis showing a clear influence of each step on the overall aroma of the spirit and, consequently, revealing clearly changing concentrations (e.g., of ethyl (S)-2-methylbutanoate, (E)-β-damascenone, ethyl (E,Z)-2,4-decadienoate, and ethyl (E,E)-2,4-decadienoate) and different aroma perceptions during the manufacturing process. In addition, the concentrations of the so-called "pear esters" ethyl (E,Z)-2,4-decadienoate and ethyl (E,E)-2,4-decadienoate were determined in 6 different pear varieties (Abate Fetel, Anjou, Bartlett, Forelle, Kaiser Alexander, and Packham's Triumph) clearly demonstrating the aroma potential of the variety Bartlett, which is mostly used for brandy production due to the high amounts of both esters eliciting a typical pear-like odor impression.

Characterization of the Key Aroma Compounds in Raw Licorice (Glycyrrhiza glabra L.) by Means of Molecular Sensory Science

Application of the molecular sensory science concept including aroma extract dilution analysis (AEDA) on the basis of gas chromatography-olfactometry combined with gas chromatography-mass spectrometry elucidated the key odorants of raw licorice (Glycyrrhiza glabra L.). Fifty aroma-active compounds were located via AEDA; 16 thereof were identified in raw licorice for the first time. γ-Nonalactone, 4-hydroxy-2,5-dimethylfuran-3(2H)-one, and 4-hydroxy-3-methoxybenzaldehyde showed the highest flavor dilution (FD) factor of 1024. Forty-three compounds were quantitated by means of stable isotope dilution analysis (SIDA; 6 more compounds were quantitated using labeled standards with structures similar to the respective analytes) and odor activity values (OAVs; ratio of concentration to the respective odor threshold) were calculated revealing OAVs ≥1 for 39 compounds. Thereby, (E,Z)-2,6-nonadienal, 5-isopropyl-2-methylphenol, hexanal, and linalool showed the highest OAVs. On the basis of the obtained results, an aqueous reconstitution model was prepared by mixing these 39 odorants in their naturally occurring concentrations. The recombinate elicited an aroma profile very similar to the profile of raw licorice, proving that all key aroma compounds were correctly identified and quantitated.

Identification and characterization of the aroma-impact components of Thai fish sauce

Comprehensive analysis of the potent odorants in Thai premium fish sauce samples was accomplished by use of complementary volatile isolation methods combined with gas chromatography-olfactometry (GC-O) and GC-mass spectrometry. Odorants of intermediate and low volatility were determined by direct solvent extraction/solvent-assisted flavor evaporation (DSE-SAFE) and aroma extract dilution analysis (AEDA). Meanwhile, static headspace dilution analysis (SHDA) and headspace solid-phase microextraction (H-SPME) were used to determine the highly volatile odorants. Results of AEDA indicated the importance (log3FD factor≥6) of five acidic odorants (butanoic acid, 3-methylbutanoic acid, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 4-hydroxy-2-ethyl-5-methyl-3(2H)-furanone, and 2-phenylacetic acid) and four neutral/basic odorants (3-methylbutanal, (Z)-1,5-octadien-3-one, phenylacetaldehyde, and o-aminoacetophone). Results of SHDA indicated the predominant (log3FD factors≥5) headspace odorants were methanethiol, 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, dimethyl trisulfide, 3-(methylthio)propanal, and butanoic acid. Concentrations for 21 odorants were determined by stable isotope dilution analysis (SIDA), and their odor-activity values (OAVs) were calculated. Among these, methanethiol, 2-methylpropanal, 3-methylbutanal, dimethyl trisulfide, 3-(methylthio)propanal, and butanoic acid had the highest OAVs (>500). Results of aroma recombination and omission studies revealed the importance of acids, aldehydes, and sulfur-containing compounds to the overall aroma of the Thai fish sauce.

Characterization of the key odorants in pan-fried white mushrooms (Agaricus bisporus L.) by means of molecular sensory science: comparison with the raw mushroom tissue

Application of aroma extract dilution analysis (AEDA) on the volatile fraction isolated from pan-fried white mushrooms ( Agaricus bisporus L.) revealed 40 odor-active compounds in the flavor dilution (FD) factor range of 8-8192, among which the caramel-like smelling 4-hydroxy-2,5-dimethylfuran-3(2H)-one showed the highest FD factor of 8192, followed by 2-propionyl-1-pyrroline (popcorn-like) and 3-hydroxy-4,5-dimethylfuran-2(5H)-one (seasoning-like). A total of 36 compounds are reported for the first time in processed mushrooms, and 25 odorants showing the highest FD factors were then quantitated by stable isotope dilution assays and their odor activity values (OAVs) were calculated as ratio of their concentrations to their odor thresholds. Among them, 3-methylbutanal (malty), 3-(methylthio)propanal (cooked potato), and 2-acetyl-1-pyrroline (popcorn-like) showed the highest OAVs (>100) in the pan-fried mushrooms, followed by 1-octen-3-one, 2-propionyl-1-pyrroline, 4-hydroxy-2,5-dimethylfuran-3(2H)-one, phenylacetaldehyde, 2,3-diethyl-5-methylpyrazine, and 3-hydroxy-4,5-dimethylfuran-2(5H)-one with OAVs >10. An aqueous aroma recombinate containing 13 odorants (OAV > 1) in their actual concentrations in the fried mushrooms showed a good similarity to the original aroma profile. The quantitation of the key odorants in raw mushrooms, identified with high FD factors during the AEDA, revealed that numerous odorants were quantitatively changed by the frying process, but in particular the concentrations of 2-phenylacetaldehyde and 3-methylbutanal were higher by factors of ∼40 and 6, respectively, compared to the amounts in the processed mushrooms. The data suggested an enzymatic formation of both Strecker aldehydes by the cut mushroom tissue. In total, 26 odorants were newly identified in raw mushrooms.

Acaricidal activities of the active component of Lycopus lucidus oil and its derivatives against house dust and stored food mites (Arachnida: Acari)

BACKGROUND

Recent studies have focused on materials derived from plant extracts as mite control products against house dust and stored food mites because repeated use of synthetic acaricides had led to resistance and unwanted activities on non-target organisms. The aim of this study was to evaluate the acaricidal activity of materials derived from Lycopus lucidus against Dermatophagoides farinae, D. pteronyssinus and Tyrophagus putrescentiae.

RESULTS

The LD50 values of L. lucidus oil were 2.19, 2.25 and 8.45 µg cm(-2) against D. farinae, D. pteronyssinus and T. putrescentiae. The acaricidal constituent of L. lucidus was isolated by chromatographic techniques and identified as 1-octen-3-ol. In a fumigant method against D. farinae, the acaricidal activity of 1-octen-3-ol (0.25 µg cm(-2)) was more toxic than N,N-diethyl-m-toluamide (DEET) (36.84 µg cm(-2)), followed by 3,7-dimethyl-1-octen-3-ol (0.29 µg cm(-2)), 1-octen-3-yl butyrate (2.32 µg cm(-2)), 1-octen-3-yl acetate (2.42 µg cm(-2)), 3,7-dimethyl-1-octene (9.34 µg cm(-2)) and benzyl benzoate (10.02 µg cm(-2)). In a filter paper bioassay against D. farinae, 1-octen-3-ol (0.63 µg cm(-2)) was more effective than DEET (20.64 µg cm(-2)), followed by 3,7-dimethyl-1-octen-3-ol (1.09 µg cm(-2)).

CONCLUSION

1-Octen-3-ol and 3,7-dimethyl-1-octen-3-ol could be useful as natural agents for the management of three mite species.

Quantification of key odorants formed by autoxidation of arachidonic acid using isotope dilution assay

Six odor-active compounds generated by autoxidation of arachidonic acid (AA) were quantified by isotope dilution assay (IDA), i.e., hexanal (1), 1-octen-3-one (2), (E,Z)-2,4-decadienal (3), (E,E)-2,4-decadienal (4), trans-4,5-epoxy-(E)-2-decenal (5), and (E,Z,Z)-2,4,7-tridecatrienal (6). Compound 1 was the most abundant odorant with about 700 mg/100 g autoxidized AA, which corresponds to 2.2 mol% yield. Based on the odor activity values (ratio of concentration to odor threshold), odorants 3 (fatty) and 5 (metallic) showed the highest sensory contribution followed by 1 (green), 2 (mushroom-like), 6 (egg white-like), and 4 (fatty). For the first time, reliable quantitative results are reported for odorants 1-6 in autoxidized AA, in particular odorant 6, which is a characteristic compound found in autoxidized AA. Synthesis of deuterated 6, required for IDA, is described in detail. The formation of odorants 1-6 by autoxidation of AA is discussed with respect to the quantitative data.