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Mead was analyzed by using the concept of molecular sensory science for the identification of key odorants. A total of 29 odor-active compounds were identified in mead by using gas chromatography olfactometry (GCO). Flavor dilution (FD) factors of identified compounds ranged from 1 to 16,384, compounds with FD factors ≥32 were quantitated by using stable isotopically substituted odorants as internal standards or external standard method, and odor activity values (OAVs) were calculated. Fifteen compounds showed OAVs ≥1: aldehydes (2-phenylacetaldehyde, 3-(methylsulfanyl)propanal), 4-hydroxy-3-methoxybenzaldehyde), esters (ethyl 3-methylbutanoate, ethyl propanoate, ethyl octanoate), alcohols (2-phenylethan-1-ol, 3- and 2-methylbutan-1-ol, 3-(methylsulyfanyl)propan-1-ol), furanons (4-hydroxy-2,5-dimethylfuran-3(2H)-one, 3-hydroxy-4,5-dimethylfuran-2(5H)-one), acids (3- and 2-methylbutanoic acid, acetic acid), 1,1-diethoxyethane, and 4-methylphenol. 2-Phenylacetaldehyde (OAV, 3100) was suggested as the compound with the biggest influence on the aroma of mead, followed by 4-hydroxy-2,5-dimethylfuran-3(2H)-one (OAV, 1900), 3-(methylsulfanyl)propanal (OAV, 890), and 2-phenylethan-1-ol (OAV, 680). Quantitative olfactory profile analysis revealed strong honey, malty, and alcoholic impressions. Omission experiments revealed that 3-(methylsulfanyl)propanal, 2-phenylethan-1-ol, 4-hydroxy-2,5-dimethylfuran-3(2H)-one, ethyl propanoate, ethyl 3-methylbutanoate, 2-phenylacetaldehyde, 3- and 2-methylbutanoic acid, 3-hydroxy-4,5-dimethylfuran-2(5H)-one, and 4-hydroxy-3-methoxybenzaldehyde were the key odorants in the mead. Determining concentrations of key odorants in important production steps showed that the fermentation and maturation stages had the strongest effect on the formation of mead aroma.

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Muscaris is a modern white grape variety with good fungal resistance and a pleasant aroma, the molecular background of which was unknown. A comparative aroma extract dilution analysis applied to Muscaris grapes and grapes of the father variety Muskateller revealed little differences and resulted in 39 and 35 odorants, respectively. Sixteen odorants exceeded their odor threshold concentrations. Odor reconstitution and omission experiments showed that the distinct lychee note in the aroma of the Muscaris grapes was generated by the combination of (2S,4R)-rose oxide and geraniol. This finding will guide further molecular research on the transfer of the lychee note into wine and may also be helpful for the targeted breeding of new grape varieties.

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Fresh kernels of the walnut tree (Juglans regia L.) show a characteristic and pleasant aroma, the molecular basis of which was unknown. The application of an aroma extract dilution analysis resulted in 50 odor-active compounds. Among them, 37 had not been reported as fresh walnut kernel volatiles before, including the two odorants with the highest flavor dilution factors, namely, fenugreek-like smelling 3-hydroxy-4,5-dimethylfuran-2(5H)-one (sotolon) and oatmeal-like smelling (2E,4E,6Z)-nona-2,4,6-trienal. Quantitations revealed 17 odorants with concentrations in the walnuts that exceeded their odor threshold concentrations. Aroma reconstitution and omission experiments finally showed that the characteristic aroma of fresh walnuts is best represented by a binary mixture of sotolon and (2E,4E,6Z)-nona-2,4,6-trienal. Of both, the natural concentration was ∼10 µg/kg. Further sensory studies showed that the walnut character is intensified when their concentrations are in parallel increased to ∼100 µg/kg. This finding may guide the future breeding of new walnut cultivars with improved aroma.

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Pea protein is a growing plant-based protein ingredient. Pea proteins have characteristic undesirable flavors, leading to challenges in ingredient applications. The objective of this study was to characterize the flavor of pea proteins using descriptive sensory analysis and instrumental volatile compound analyses. Seven sensory attributes were identified in most pea proteins at variable intensities: cereal/grain, cardboard, green pea, beany/yellow pea, bitter, umami, and astringent. Other attributes, cheesy, doughy, sulfur, pyrazine, fecal, sweet aromatic and salty taste, were distinguishing flavors of some pea proteins (p < 0.05). The key aroma-active compounds in pea proteins were hexanal, heptanal, benzaldehyde, methional, 2-hexanone, 2-heptanone, 1-octen-3-one, 2-nonanone, 1-nonen-3-one, 1-pentanol, 2-pentyl furan, 2-isopropyl-3-methoxypyrazine, 2,5-dimethyl-3-(3-methylbutyl)-pyrazine and 2-methyl-isoborneol (present in all representative samples). Volatile compounds responsible for the majority of sample variation included 2-methyl butanal, (Z)-3-hexanal, (E,E)-2,4-decadienal, 1-octen-3-one, 2-decanone, 1-pentanol, 1-octen-3-ol, geosmin and 2,3-diethyl-5-methyl pyrazine (p < 0.05). This study can facilitate product development and flavor masking of various pea protein applications.

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The effect of seasonal and regional differences of rainbow trout on its aroma and aroma-active profile was investigated. Solvent-assisted flavor evaporation (SAFE) procedure was employed for the aroma extraction while Gas Chromatography-Mass Spectrometry-Olfactometry (GC-MS-O) and aroma extract dilution analysis (AEDA) were utilized to assess the aroma-active substances. The olfactometric analysis indicated seasonal and regional differences in the aroma-active compounds contributing to the characteristic odours of the trout samples and the compounds were more intense in autumn and winter. The strongest aroma-actives were hexanal (green), acetoin (buttery, green), limonene (citrus), 2-hexanol (green, pungent) and 1-octen-3-ol (oily, mushroom). The findings of this study can provide useful information for the selection of rainbow trout based on the seasons and locations in terms of marketing and consumer preference.

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The leaf of moso bamboo (Phyllostachys pubescens Mazel) is rich in odorant compounds, which is important natural materials for the production of flavor. It also contains phenolic acids, amino acids and peptides, which is a potential source of natural bioactive compounds. The study of odor-active compounds in bamboo leaves can provide a basis for the discovery of natural flavor. The leaf, stem, and powder of moso bamboo were analyzed by gas chromatography-ion mobility spectrometry (GC-IMS). Main odor-active compounds in moso bamboo leaf were analyzed and characterized by (1) a gas chromatography olfactory mass spectrometry (GC-O-MS), (2) two-dimensional gas chromatography olfactory mass spectrometry (GC × GC-O-MS) and (3) electronic nose (E-nose). Based on aroma extract dilution analysis (AEDA), 13 key odor-active compounds with high flavor dilution (FD) factor (≥27), including 3-methyl-1-butanol, (E)-2-hexenal, ethyl hexanoate, (Z)-4-heptenenal, 6-methyl-5-hepten-2-one, octanal, ethyl (Z)-3-hexenoate, 1-hexanol, (Z)-3-hexen-1-ol, (E, E)-2,4-heptadienal, (Z)-2-hexen-1-ol, 1-octen-3-ol and benzaldehyde, were further analyzed. The compounds detected by the above four methods were (E)-2-hexenal, 6-methyl-5-hepten-2-one, octanal, (E, E)-2,4-heptadienal, 1-octen-3-ol and benzaldehyde, and all of which were the main and potential odorants of moso bamboo leaf.

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This study was to understand characteristic aroma properties of kale tea made by roasting kale leaves by profiling its aroma composition and screening its aroma-active compounds. Secondary metabolites of glucosinolates such as ally isothiocyanate, 3-butenyl isothiocyanate, 3-methylthiopropyl isothiocyanate, and 5-methylthiazole were the primary aroma compounds of raw kale but were less abundant in kale tea. Dimethyl trisulfide, cyclohex-2-en-1-ol, benzeneacetaldehyde, and 4-vinylguaiacol were quantitatively major aroma compounds in kale tea. Pyrazines, aldehydes, sulfides, and 4-vinylguaiacol were newly produced only in kale tea. In particular, 2-ethyl-6-methylpyrazine exhibiting the highest flavor dilution factor was the most potent aroma-active compound of kale tea, followed by methional, 2-ethyl-5-methylpyrazine, 2,5-dimethylpyrazine, 2,6-dimethylpyrazine, two unknown compounds, dimethyl disulfide, furfural, benzaldehyde, and dimethyl trisulfide. These compounds contributed to roasted, sulfur-like/pungent, and sweet aroma characteristics, which were main aroma properties of kale tea. In addition, (E)-hex-2-enal and (Z)-hex-3-en-1-ol contributed to the green and grassy aromas of kale tea.

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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.

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Aroma compounds in Cascade and Chinook hops harvested from multiple Virginia locations were identified by gas chromatography-mass spectrometry-olfactometry (GC-MS-O) and aroma extract dilution analysis (AEDA). Selected aroma compounds were quantitated by combination of stable isotope dilution analysis (SIDA) and standard addition method (SAM). A total of 33 aroma-active compounds were detected in five samples with ß-myrcene, methyl octanoate, geraniol and linalool being the predominant compounds based on their high flavor dilution (FD) factors and odor activity values (OAVs). L-Calamenene and germacrene B was the major characteristic component unique to Cascade and Chinook variety, respectively. Principal component analysis (PCA) showed distinctive aroma profiles for all samples except for Blacksburg and Petersburg Cascade. Hierarchical cluster analysis (HCA) reflected the higher contents of most aroma-active compounds in Meadowview Cascade and Chinook when compared to their counterparts. The significant variations suggested the potential influences of environmental factors and agronomic practices on hop aroma quality.

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Specialty barley malts provide unique aroma characteristics to beer; however, the transfer of specialty malt odorants to beer has not yet been systematically studied. Therefore, three beers were brewed: (1) exclusively with kilned base barley malt, (2) with the addition of a caramel barley malt, and (3) with the addition of a roasted barley malt. Major odorants in the beers were identified by aroma extract dilution analysis followed by quantitation and calculation of odor activity values (OAVs). The caramel malt beer was characterized by outstandingly high OAVs for odorants such as (E)-ß-damascenone, 2-acetyl-1-pyrroline, methionol, 2-ethyl-3,5-dimethylpyrazine, and 4-hydroxy-2,5-dimethylfuran-3(2H)-one, whereas the highest OAV for 2-methoxyphenol was obtained in the roasted malt beer. Quantifying odorants in the malts revealed that the direct transfer from malt to beer played only a minor role in the amount of malt odorants in the beers, suggesting a substantial formation from precursors and/or a release of encapsulated odorants during brewing.

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An insight using molecular sensory science approaches to the contributions and variations of the key odorants in shiitake mushrooms is revealed in this study. Odorants were extracted by headspace solid phase microextraction (HS-SPME) and direct solvent extraction combined with solvent-assisted flavor evaporation (DSE-SAFE) in fresh and hot-air-dried shiitake mushrooms. Among them, 18 and 22 predominant odorants were determined by detection frequency analysis (DFA) and aroma extract dilution analysis (AEDA) combined with gas chromatography-olfactometry (GC-O) in the fresh and dried samples, respectively. The contributions of these predominant odorants in the food matrix were determined by quantification and odor activity values (OAVs) with aroma recombination verification. There were 13 and 14 odorants identified as key contributing odorants to overall aroma, respectively. 1-Octen-3-ol and 1-octen-3-one were the most key contributing odorants in the fresh samples in contributing mushroom-like odor. After hot-air-drying, the OAV and concentrations on dry basis of the key contributing odorants changed, due to oxidation, degradation, caramelization and Maillard reactions of fatty acids, polysaccharides and amino acids. 1-Octen-3-ol was reduced most significantly and degraded to 1-hydroxy-3-octanone, while phenylethyl alcohol increased the most and was formed by phenylalanine. In hot-air-dried samples, lenthionine became the most important contributor and samples were characterized by a sulfury odor. Overall contributions and variations of odorants to the aroma of shiitake mushrooms were revealed at the molecular level.

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The parallel application of aroma extract dilution analysis to the volatiles isolated from a sample of fermented cocoa seeds with a pronounced moldy-musty off-flavor and to the volatiles isolated from a flawless reference sample revealed (-)-geosmin, 4-methoxy-2,5-dimethylfuran-3(2H)-one, 1H-indole, and 3-methyl-1H-indole as potential off-flavor compounds on the basis of their odor quality and higher flavor dilution factors in off-flavor cocoa than in the reference sample. Quantitation of the four compounds in nine off-flavor cocoa samples and calculation of odor activity values (ratio of the concentrations to the odor threshold values) suggested the crucial roles of (-)-geosmin and 3-methyl-1H-indole for the off-flavor. In the chocolate industry, their quantitation can be used to objectively assess the off-flavor at the level of incoming goods inspection. Because both compounds are inhomogeneously distributed between the testa and the embryo, separate quantitation in the two parts of the seeds is required.

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Screening the volatiles isolated from a standard polypropylene material consisting of a polypropylene homopolymer, the filler talcum, and a mixture of antioxidants, for odor-active compounds by application of an aroma extract dilution analysis revealed 30 odorants with flavor dilution factors ranging from 1 to 64. Eighteen odor-active compounds were subsequently quantitated by gas chromatography-mass spectrometry using stable isotopically substituted odorants as internal standards, and their odor activity values (OAVs) were calculated as ratios of the concentrations to the odor threshold values. Five odorants showed OAVs ≥1, among which were hex-1-en-3-one (OAV 12), butanoic acid (OAV 3), as well as 4-methylphenol, butan-1-ol, and 2-tert-butylphenol (all OAV 1). A comparative analysis of polypropylene materials with different additives suggested plastic-like, pungent smelling hex-1-en-3-one as an ubiquitous key odorant. Odor-active amounts of alkylphenols, in particular plastic-like, phenolic smelling 2-tert-butylphenol, were additionally formed in the presence of talcum and phenolic antioxidants. Whereas the precursors of the phenols were thus obvious, the origin of hex-1-en-3-one was unknown. Injection molding showed only little influence on odorant concentrations.

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The aroma profile of raw pu'er tea (RPT) depends on its storage duration (2-10 years) and storage conditions (wet-hot or dry-cold environment). We analyzed the major odorants of RPT samples by performing metabolomic analysis and by using the molecular sensory science approach. Under dry-cold storage conditions, tea leaves had more carotenoid derivatives, glycoside-derived volatiles, and phenolic volatiles, resulting in "fresh," "floral," and "sweet" aroma. Under wet-hot storage conditions, tea leaves had more methoxybenzenes, which contributed considerably to their "stale" and "woody" aroma. We identified 11 and 4 compounds as the odor markers of RPTs when stored in dry-cold and wet-hot environments, respectively. Our findings provide a scientific basis for optimal storage that yields the desired aroma profile.

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Activity of odor compounds of soy sauces has not been fully determined so far. Herein, a new switchable GC/GC × GC-olfactometry-mass spectrometry system for simultaneous GC × GC-MS analysis and sniffing of each odor-active substance through a single injection was used for the aroma extract dilution analysis of five regular high-salt liquid-state soy sauces (HLS). Methional, maltol, guaiacol, 4-ethylguaiacol, 2-acetylpyrrole, 2-acetylfuran, 2-phenylethanol, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone showed high flavor dilution (FD) factors. The FD factors of all odor-active compounds in different odor attributes were summed up (score) to evaluate the odor characteristics of the samples. Cooked potato-like odor was the most important characteristic. The difference in the odor characteristics were mainly reflected in the balance of caramel-like/sweet, roasted/roasted nut-like, spicy/burnt, and unpleasant odor intensity; the fruity odor intensity was the weakest. This study will provide a better understanding of the odor characteristics and key odor-active compounds in Chinese regular commercial HLS.

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'Honeycrisp' is a popular apple cultivar because of its superior appearance and flavor. We investigated its aroma profiles and characteristic aroma. Whereas the aroma profiles of developing fruits were dominated by aldehydes, postharvest fruit accumulated abundant esters, alcohols, and sesquiterpenoids. Most of these components showed maxima at the fruit's climacteric peak. There were more types and higher contents of sesquiterpenoids, aldehydes, and esters in the fruit skin than in the pulp, while alcohol contents and types were comparable between the pulp and skin. Aroma extract dilution and gas chromatography-olfactometry analyses revealed that hexyl 2-methylbutyrate, α-farnesene, 1,3-octanediol, hexanal, (E)-2-hexenal, hexanol, butanol, and 2-methyl-butanol are the most potent odor compounds in 'Honeycrisp' apple. Aroma reconstruction and omission tests combined with sensory analyses suggested that hexyl 2-methylbutyrate is responsible for the strong fruity note of 'Honeycrisp' apple, and that other alcohols, aldehydes, and α-farnesene are essential for its background aroma notes.

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Yeast extract (YE) is rich in amino acids, nucleotides, peptides, and other flavor substances, and is a natural nutrient, umami, and flavor enhancer. However, certain YE samples impart a yeasty flavor that affects the quality parameters of YE. We compared solid-phase microextraction (SPME), solvent-assisted evaporation (SAFE), dynamic headspace sample preparation (DHS), stir bar sorptive extraction (SBSE), and other pretreatment methods for the extraction of volatiles substances in YE. SPME was selected as a suitable extraction method, and aroma extract dilution analysis (AEDA) was combined with gas chromatography-olfactometry-mass spectrometry (GC-O-MS) for identification of key odor-active compounds in 23 YE samples. The yeast off-odor substances were screened from these compounds. Principal component analysis (PCA) was used to investigate the relationship between strains and the processing of YE products and their yeasty flavor. PRACTICAL APPLICATIONS: YE is prepared primarily from baker's yeast or waste beer yeast by autolysis or enzymatic hydrolysis, and is rich in nucleotides, peptides, amino acids, and other flavor compounds. It is used globally as a common umami and flavor enhancer. However, consumers have observed that YE imparts a certain yeasty flavor that influences the overall flavor negatively. Hence, the yeasty flavor-imparting substances from 23 YE samples were investigated in this study, and the observations (including strains, processing techniques, etc.) were integrated to explain the relationship between the yeasty flavor of the YE products with strain (different yeast strain for production) or processing of YE products (enzymes used, enzymatic hydrolysis conditions, composition of products, concentration conditions of YE, etc.), or storage conditions (temperature, humidity, duration, package, etc.), providing a scientific basis for removal/lowering or masking of yeasty flavor and the improvement of flavor quality of YE products.

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The Fondillón is a wine made from overripe grapes of the Monastrell variety, which is characterized by a high alcohol content and a minimum barrel ageing of 10 years. The objective of this study was to analyze the Fondillón volatile composition, key aroma-active compounds, sensory profile and phenolic composition. Fifty-four volatile compounds were identified, quantified and classified as alcohols, esters, acids, aldehydes, lactones, phenols, hydrocarbons and ketone. From these compounds, 22 aroma-active compounds were identified, with phenylethyl alcohol, diethyl succinate and ethyl lactate having the highest flavor dilution factor. The Fondillón wines were characterized by having high intensity of alcohol, fruity and toasted odor and flavor notes, and long aftertaste. Besides, 25 phenolic compounds were also identified and quantified; the phenolic acids (gallic, protocatechuic and syringic acids) were the predominant phenolic compounds.

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Screening the volatiles of cempedak [Artocarpus integer (Thunb.) Merr.] pulp for odor-active compounds by aroma extract dilution analysis and gas chromatography (GC)-olfactometry of static headspace samples revealed a total of 55 odorants, among which 47 were identified. Using stable isotopically substituted odorants as internal standards, these compounds were quantitated by GC-mass spectrometry, and odor activity values (OAVs) were calculated as ratios of the natural concentrations in cempedak pulp to the orthonasal odor detection thresholds. An aroma reconstitution model based on the 41 compounds with OAVs >1 in their natural concentrations successfully mimicked the characteristic aroma of cempedak pulp including the pronounced sulfury, oniony note which is intense in cempedak pulp but absent in jackfruit pulp. Further sensory tests finally showed that 2-(methylsulfanyl)propane, 2-(methylsulfanyl)butane, and 2-(methylsulfanyl)pentane are the key compounds responsible for this unique aroma note in cempedak pulp and vitally contribute to the aroma difference between cempedak pulp and jackfruit pulp.

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Solid-phase microextraction (SPME), purge and trap (P&T), stir bar sportive extraction (SBSE), and dynamic headspace sampling (DHS) were applied to extract, separate and analyze the volatile compounds in the roots of Hangbaizhi, Qibaizhi, and Bobaizhi and the GC-O-MS/MS (AEDA) was utilized for the quantification of key aroma compounds. Totals of 52, 54, and 43 aroma-active compounds extracted from the three samples by the four extraction methods were identified. Among these methods, the SPME effectively extracted the aroma compounds from the A. dahurica. Thus, using the SPME methods for quantitative analysis based on external standards and subsequent dilution analyses, totals of 20, 21, and 17 aroma compounds were detected in the three samples by the sniffing test, and sensory evaluations indicated that the aromas of A. dahurica included herb, spice, and woody. Finally, principal component analysis (PCA) showed that the three kinds A. dahurica formed three separate groups, and partial least squares discriminant analysis (PLS-DA) showed that caryophyllene, (-)-ß-elemene, nonanal, and ß-pinene played an important role in the classification of A. dahurica.

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