The characteristic of the key aroma-active components in white tea using GC-TOF-MS and GC-olfactometry combined with sensory-directed flavor analysis.

BACKGROUND: White tea has become more and more popular with consumers due to its health benefits and unique flavor. However, the key aroma-active compounds of white tea during the aging process are still unclear. Thus, the key aroma-active compounds of white tea during the aging process were investigated using gas chromatography-time-of-flight-mass spectrometry (GC-TOF-MS) and gas chromatography-olfactometry (GC-O) combined with sensory-directed flavor analysis. RESULTS: A total of 127 volatile compounds were identified from white tea samples with different aging years by GC-TOF-MS. Fifty-eight aroma-active compounds were then determined by GC-O, and 19 of them were further selected as the key aroma-active compounds based on modified frequency (MF) and odor activity value (OAV). CONCLUSION: Aroma recombination and omission testing confirmed that 1-octen-3-ol, linalool, phenethyl alcohol, geraniol, (E)-ß-ionone, α-ionone, hexanal, phenylacetaldehyde, nonanal, (E, Z)-(2,6)-nonadienal, safranal, γ-nonalactone and 2-amylfuran were the common key aroma-active compounds to all samples. Cedrol, linalool oxide II and methyl salicylate were confirmed peculiar in new white tea, while ß-damascenone and jasmone were peculiar in aged white tea. This work will offer support for further studies on the material basis of flavor formation of white tea. © 2023 Society of Chemical Industry.

Characterization of the key odorants in kurut with aroma recombination and omission studies.

Kurut is a traditional acid-coagulated cheese from the northwest region of China. Using gas chromatography olfactometry and aroma extract dilution analysis, we identified 21 potent odorants from kurut within the flavor dilution factor range of 8 to 256. We developed a kurut matrix to determine the odor thresholds of key aroma compounds in kurut. The odor activity values of these 21 potent volatile compounds revealed that 18 were present at concentrations above their odor threshold values and therefore contributed to the overall aroma of kurut. The result of aroma recombinant experiments prepared by mixing the 18 most important odorants at the concentrations in which they occurred in kurut showed that the overall aroma profile of the recombinant sample was very similar to that of kurut. Omission experiments indicated that acids, furans, esters, and ketones were the most important volatile compounds in kurut. Some aroma compounds-such as butanoic acid, homofuraneol, ethyl hexanoate, and ethyl butanoate-play the most important roles in the overall flavor profile of kurut. Some odorants with a high flavor dilution factor, such as sulfur compounds, may have little effect. The study of key aroma compounds in kurut could provide important information for researching and developing traditional Chinese cheese products.

Flavoromics approach to identifying the key aroma compounds in traditional Chinese milk fan.

To determine the key aroma compounds in Chinese milk fan cheese, samples from 6 of the most popular handmade milk fan workshops in Yunnan province of China were analyzed by gas chromatography-mass spectrometry (GC-MS), gas chromatography-olfactometry (GC-O), sensory evaluation, aroma recombination and omission experiments. Seventy-one aroma compounds were identified by GC-MS, and 31 odor-active compounds were detected by GC-O. The relationships between the 31 odor-active compounds and 10 sensory evaluation properties were explored by partial least squares discriminant analysis. The results identified 23 initial key aroma compounds, which were used to simulate the aroma profile of milk fan in aroma recombination experiments. Aroma omission experiments identified propanoic acid, butanoic acid, octanoic acid, octanal, nonanal, 2-nonanone, and ethyl hexanoate as the key aroma compounds. Propanoic acid and butanoic acid contributed to cheese and rancid aromas, octanal and nonanal to the fat aroma, octanoic acid and 2-nonanone to the cheese aroma, and ethyl hexanoate to the fruity aroma of milk fan.

Identification of the key aroma compounds in flaxseed milk using stir bar sorptive extraction, aroma recombination, and omission tests.

Flaxseed milk is a plant-based dairy alternative that is rich in nutrients. Due to the low concentration of odor compounds in flaxseed milk, it cannot be completely extracted. This poses significant challenges for analysis. Therefore, this study developed a method suitable for extracting volatile compounds from flaxseed milk and compared it with three other extraction methods. It was found that Stir Bar Sorptive Extraction had the best extraction performance, identifying 39 odorants. Flavor dilution factors ranged from 1 to 512, with higher values observed for esters. 13 key odor compounds were identified (odor activity value > 1) using the external standard method for quantification; these included four aldehydes, three pyrazines, two alcohols, two esters, and two other compounds. Pyrazine compounds exhibited the highest concentrations. Aroma recombination and omission experiments showed that nine key odorants contributed significantly to the flavor profile of flaxseed milk, imparting aroma of cucumber, green, mushroom, fruity, sweet, and coconut.

Characterization of key aroma-active compounds in different types of Douchi based on molecular sensory science approaches.

To attain the differences in the flavor profile of Douchi, the key aroma-active compounds of three types of Douchi were investigated. The "Sauce-like", "Smoky", "Nutty", "Roast", "Caramel", and "Flower" of Douchi were favored by customers. Further, a total of 179 volatile compounds were identified using HS-SPME-GC-MS, and 29 aroma compounds were detected using GC-O-MS. Based on the quantification, 9, 13, and 10 compounds were regarded as aroma-active compounds in Yangjiang Douchi (YJ), Pingjiang Douchi (PJ), and Liuyang Douchi (LY), respectively. Moreover, the mixture of these aroma-active compounds successfully simulated the main aromas of PJ, LY, and YJ. And omission experiments confirmed that guaiacol was the key aroma compound for LY, benzene acetaldehyde, dimethyl trisulfide, and 2-acetyl pyrrole were important for YJ, benzene acetaldehyde and 3,5-diethyl-2-methyl pyrazine notably contributed to key aroma of PJ.

Variations in Key Aroma Compounds and Aroma Profiles in Yellow and White Cultivars of Flammulina filiformis Based on Gas Chromatography-Mass Spectrometry-Olfactometry, Aroma Recombination, and Omission Experiments Coupled with Odor Threshold Concentrations.

Flammulina filiformis (F. filiformis) is called the 'benefiting intelligence' mushroom. There is a notable difference between a yellow cultivar (with a robust aroma) and a white mutant cultivar (with a high yield) of F. filiformis. A thorough analysis of aroma differences is essential to improve the aroma of high-yield strains. This study employed a combination of gas chromatography-mass spectrometry-olfactometry (GC-MS-O) and aroma extract dilution analysis (AEDA) to analyze the variations in aroma compounds. Then, the contribution of the odorants was determined using flavor dilution (FD) factors and odor activity values (OAVs). Aroma omission and recombination experiments were used to identify the key odorants. A total of 16 key aroma compounds were characterized in F. filiformis, along with four eight-carbon volatiles (3-octanone, 3-octanol, octanal, and 1-octen-3-ol). Finally, the dominant aroma characteristic was "sweet" for the yellow strain, while it was "green" for the white strain. More research is required to investigate the enzymes and corresponding genes that regulate the synthesis of aroma compounds in F. filiformis for future breeding programs.

Characterization of Key Odorants in Chinese Texiang Aroma and Flavor Type Baijiu (Chinese Liquor) by Means of a Molecular Sensory Science Approach.

The popularity of texiang aroma type baijiu (liquor), known for its unique production technology and multilayered flavor, has been steadily increasing among consumers. So far, no research has determined its key aroma compounds for characterizing the unique flavor, which is the purpose of this paper. Using gas chromatography-olfactometry (GC-O) coupled with the GC-mass spectrometry (GC-MS) method, 87 aroma-active compounds were identified and screened out with intensity values ≥2.0. 1,1,6-Trimethyl-1,2-dihydronaphthalene (TDN) was first confirmed by GC-O in Chinese liquor. According to a quantitative study and odor activity values (OAVs), 42 odorants were determined as important aroma compounds. These odorants were recombined based on quantitative concentrations, successfully simulating the overall aroma profile. Omission experiments verified ethyl hexanoate, ß-damascenone, and 2-furfuryl ethyl ether as the key aroma compounds and revealed that ethyl acetate, furfural, and ethyl 2-phenylacetate were important aroma compounds to the overall flavor of texiang aroma and flavor type liquor.

Sensomics-Assisted Characterization of Fungal-Flowery Aroma Components in Fermented Tea Using Eurotium cristatum.

Fermented tea (FT) using a single Eurotium cristatum strain can produce a pleasant fungal-flowery aroma, which is similar to the composite aroma characteristic of minty, flowery, and woody aromas, but its molecular basis is not yet clear. In this study, solvent-assisted flavor evaporation and gas chromatography-mass spectrometry/olfactometry were applied to isolate and identify volatiles from the FT by E. cristatum. The application of an aroma extract dilution analysis screened out 43 aroma-active compounds. Quantification revealed that there were 11 odorants with high odor threshold concentrations. Recombination and omission tests revealed that nonanal, methyl salicylate, decanoic acid, 4-methoxybenzaldehyde, α-terpineol, phenylacetaldehyde, and coumarin were the major odorants in the FT. Addition tests further verified that methyl salicylate, 4-methoxybenzaldehyde, and coumarin were the key odorants for fungal-flowery aroma, each corresponding to minty, woody, and flowery aromas, respectively. 4-Methoxybenzaldehyde and coumarin were newly found odorants for fungal-flowery aroma in FT, and 4-methoxybenzaldehyde had not been reported as a tea volatile compound before. This finding may guide future industrial production optimization of FT with improved flavor.

Sensomics-Assisted Characterization of Key Flowery Aroma Compounds in Lu'an Guapian Green Tea Infusion (Camellia sinensis).

The volatile fraction was isolated from the premium and common grade of Lu'an Guapian green tea infusion by solvent-assisted flavor evaporation distillation. With the application of aroma extract dilution analysis, a total of 52 aroma-active compounds were revealed in the flavor dilution (FD) factor area of 32-8192. Besides, five additional odorants with higher volatility were identified using solid-phase microextraction. The aroma profiles, FD factors, and quantitative data of premium Guapian (PGP) and common Guapian (CGP) showed apparent differences. The intensity of the flowery attribute was significantly higher in PGP than in CGP, while cooked vegetable-like was the most outstanding odor note in CGP. The recombination experiment and the omission test of PGP clarified that dimethyl sulfide, (E,E)-2,4-heptadienal, (E)-ß-ionone, (E,Z)-2,6-nonadienal, 2-methylbutanal, indole, 6-methyl-5-hepten-2-one, hexanal, 3-methylbutanal, γ-hexalactone, methyl epijasmonate, linalool, geraniol, and (Z)-3-hexen-1-ol were the key odorants of PGP tea infusion. The omission and addition tests of flowery odorants manifested that (E)-ß-ionone, geraniol, and (E,E)-2,4-heptadienal, with higher odor activity values in PGP than in CGP, contributed to the flowery attribute most. The difference in the concentration of the abovementioned odorants with flowery odor notes could be one of the main factors which led to the difference in aroma quality between the two grades of Lu'an Guapian.

Characteristic aroma-active components of fried green onion (Allium fistulosum L.) through flavoromics analysis.

Green onion (Allium fistulosum L.) is a perennial herb with a characteristic allium aroma. Meanwhile, fried green onion oil has a rich flavor that is popular in traditional Chinese cuisine. In this work, the key aroma components of fried green onion oil were focused via flavoromics analysis. The oil samples had a low score of a green aroma but a high score of salty, greasy aromas. Whereafter, a total of 36 aroma-active substances with flavor dilution (FD) factors ranging from 1 to 6561 were identified in fried green onion oil, while 42 were detected in fried green onion residue with FD factors ranging from 1 to 19683. Additionally, the recombination and omission tests revealed that furaneol, dimethyl trisulfide, allyl methyl trisulfide, (E,E)-2,4-decadienal, etc., were the key aroma compounds in fried green onion oil. Furthermore, the observation of the reaction of thioethers at high temperatures revealed that dimethyl disulfide undergoes polymerization to form dimethyl trisulfide. The research results can provide a theoretical basis for the standardization and industrial production of Chinese cuisine.

Characterization of the key odor-active compounds in different aroma types of Fu brick tea using HS-SPME/GC-MSO combined with sensory-directed flavor analysis.

Fu brick tea (FBT) is popular for its unique 'fungal flower' aroma, however, its key odor-active compounds are essentially unknown. In this study, the odor-active compounds of "stale-fungal" aroma (CJX), "fresh-fungal" aroma (QJX), and "fermentation-fungal" aroma (FJX) types FBT were extracted and examined by headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and gas chromatographyolfactometry (GC-O). A total of 43 volatile and 38 odor-active compounds were identified by these methods. Among them, the content of dihydroactindiolide (4596-13189 µg/L), (E)-linalool oxide (2863-6627 µg/L), and benzyl alcohol (4992-6859 µg/L) were highest. Aroma recombination experiments further verified that these odor-active compounds could be simulated the overall aroma profile of FBT successfully. Furthermore, omission experiments confirmed that 15, 20, and 15 key odor-active compounds in CJX, QJX, and FJX FBT, respectively. This study will provide a theoretical basis for comprehensively understanding the formation of characteristic aromas in FBT.

Characterization of the key aroma compounds in aged Chinese Xiaoqu Baijiu by means of the sensomics approach.

The aromatic characteristics of Xiaoqu Baijiu differ noticeably and were investigated using the sensomics approach. Aroma extract dilution analysis revealed more aroma-active compounds in aged Xiaoqu Baijiu than fresh Xiaoqu Baijiu, with 55 compounds identified with flavor dilution (FD) factors of ≥8. Using sensomics, 51 odorants were identified as important aroma compounds in aged Xiaoqu Baijiu. Omission models suggested that 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon), vanillin, and 3-(methylthio)propionaldehyde (methional) played critical roles in the overall aroma characteristics of aged Xiaoqu Baijiu. Furthermore, 1,1-dimethoxyethane, 3-methylbutanal, dimethyl trisulfide, ethyl acetate, and ethyl isovalerate also exhibited significant roles in the aroma characteristics of aged Xiaoqu Baijiu. This work may provide a better understanding on Chinese Xiaoqu Baijiu and the changes of aroma compounds during the aging process of liquor.

Characterization of the key aroma-active compounds in high-grade Dianhong tea using GC-MS and GC-O combined with sensory-directed flavor analysis.

Dianhong tea (DHT) is popular for its pleasant caramel-like aroma. In this study, the aroma profile of high-grade DHT have been studied using gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O) combined with headspace solid phase microextraction (HS-SPME). A total of 52 aroma-active compounds were identified by GC-O coupled with aroma extract dilution analysis (AEDA) and odor specific magnitude estimation (Osme). Among them, quantification of 21 aroma-active compounds indicated that the content of linalool (5928 µg/kg) was the highest in high-grade DHT, followed by phenylethanol (3923 µg/kg) and phenylacetaldehyde (1801 µg/kg). Sensory-directed aroma recombination and omission tests further verified that phenylacetaldehyde, linalool, geraniol and 3-ethyl-2,5-dimethylpyrazine were important contributors to the overall sensory characteristics of high-grade DHT which dominated mainly by floral, sweet and caramel-like odors. This work will provide a theoretical reference for comprehensively understanding the aroma characteristic of DHT.

Characterisation of the key volatile compounds of commercial Gouda cheeses and their contribution to aromas according to Chinese consumers' preferences.

A systematic flavoromics-based analysis of samples of 12 commercially available Gouda cheeses was performed to determine their key volatile components, the contribution of these components to the aromas of the cheeses, and which aromas were preferred by a panel of Chinese consumers. The sensory analysis results show that the Chinese consumers preferred young and medium cheeses, and that sensory attributes such as 'milk' and 'cream' were the most popular. Seventy-seven aroma compounds were identified by gas chromatography-mass spectrometry, and 28 of these were determined to be aroma-active compounds by gas chromatography-olfactometry analysis and calculation of their odour activity values. Partial least-squares analysis revealed that compounds such as diacetyl and acetoin correlated with aromas preferred by the Chinese consumers, while isobutyric acid, hexanoic acid and valeric acid correlated with aromas disliked by the Chinese consumers. Finally, the flavour contribution of each aroma-active compound was validated through aroma reorganisation and omission experiments.

Variation in Volatile Compounds of Raw Pu-Erh Tea upon Steeping Process by Gas Chromatography-Ion Mobility Spectrometry and Characterization of the Aroma-Active Compounds in Tea Infusion Using Gas Chromatography-Olfactometry-Mass Spectrometry.

Steeping process is an important factor for aroma release of tea, which has rarely been investigated for the aroma changes of raw Pu-erh tea (RAPT). In addition, the comprehensive aroma characteristics identification of RAPT infusion is necessary. In this study, GC-IMS coupled with principal component analysis (PCA) was used to clarify the difference of volatile profiles during the steeping process of RAPT. Furthermore, the volatiles contained in the RAPT infusion were extracted by three pretreatment methods (HS-SPME, SBSE, and SAFE) and identified using GC-O-MS. According to the odor activity value, 28 of 66 compounds were categorized as aroma-active compounds. Aroma recombination and omission experiments showed that "fatty", "green", "fruity", and "floral" are considered to be the main aroma attributes of RAPT infusion with a strong relationship with 1-octen-3-one, 1-octen-3-ol, (E)-2-octenal, ß-ionone, linalool, etc. This study will contribute a better understanding of the mechanism of the RAPT steeping process and volatile generation.

Characterization of key odorants in fried red and green huajiao (Zanthoxylum bungeanum maxim. and Zanthoxylum schinifolium sieb. et Zucc.) oils.

Fried huajiao oil (FHO) samples prepared with red or green huajiao are widely applied in different Chinese cuisines due to their own aroma characteristics. To investigate their different aroma profiles, 2 red and 3 green FHOs were analyzed by quantitative descriptive sensory analysis (QDA) and gas chromatography-olfactometry/aroma intensity (GC-O/AI). QDA results showed a distinct difference among FHOs in terms of all sensory attributes. Thirty odorants with high OAVs and AIs were screened from 5 FHOs, among which ß-myrcene, (E)-2-heptenal, limonene, α-terpineol and p-cymene were the major characteristic compounds of FHOs. In addition, through orthogonal partial least square discriminate analysis (OPLS-DA), linalool, linalyl acetate, and 1,8-cineole were considered as the volatile markers for classification of FHOs with red and green huajiao. Thereafter, aroma recombination and omission tests were performed to characterize the key aroma compounds of red and green FHOs.

Characterization of Key Odorants in Hanyuan and Hancheng Fried Pepper (Zanthoxylum bungeanum) Oil.

Fried pepper (Zanthoxylum bungeanum Maxim.) oil has been widely used in traditional Chinese cuisine and has recently become increasingly popular in food manufacturing. Thus, the aroma profiles of Hancheng pepper oil (HCPO) and Hanyuan pepper oil (HYPO) from two regions were investigated by aroma extract dilution analysis (AEDA) combined with gas chromatography-mass spectrometry-olfactometry (GC-MS-O). Results from AEDA showed that more aroma compounds with flavor dilution factors ≥9 were detected in HCPO than in HYPO. The odor activity values (OAVs) revealed 28 odorants with OAVs ≥1 in HCPO or HYPO. High OAVs were in particular obtained for 1,8-cineole, (E)-2-heptenal, ß-myrcene, ß-ocimene, limonene, and linalool. Then, the aroma profiles of HCPO and HYPO were successfully simulated through aroma recombination models. Omission tests suggested that ß-phellandrene, p-cymene, acetic acid octyl ester, octanal, citronellol, and sabinene played key roles in aroma differences between HCPO and HYPO. In addition, varying enantiomeric ratios of linalool (floral) and limonene (citrus-like and lemon-like) in HCPO and HYPO were observed by chiral GC-MS, and the odor impressions of limonene and linalool were in good agreement with the odor descriptions of S-(-)-limonene and S-(+)-linalool.

Characterization of the Key Aroma Compounds in Aged Chinese Rice Wine by Comparative Aroma Extract Dilution Analysis, Quantitative Measurements, Aroma Recombination, and Omission Studies.

The aroma compounds in young and aged Chinese rice wines (rice wines) with a clear difference in their overall aroma profiles were analyzed by comparative aroma extract dilution analysis (cAEDA). In AEDA, more aroma-active regions with flavor dilution (FD) factors of ≥64 were detected in the aged rice wine than in the young rice wine. A total of 43 odorants were further identified and quantitated. The odor activity values (OAVs) revealed 33 aroma compounds with OAVs of ≥1 in young or aged rice wine. Among these aroma compounds with relatively higher OAVs, 3-methylbutanoic acid, 1,1-diethoxyethane, vanillin, 3-methylbutanal, sotolon, benzaldehyde, 4-vinylguaiacol, methional, and 2,3-butanedione showed significant differences between young and aged rice wines. This difference was confirmed through a quantitative analysis of 34 rice wine samples with ages of 0-15 years. Then, the aroma profile of the aged rice wine was successfully simulated through an aroma recombination model. Omission models suggested that sotolon, vanillin, 3-methylbutanal, and benzaldehyde played key roles in the overall aroma of aged rice wine.

Characterization of the Key Aroma Compounds in Chinese Vidal Icewine by Gas Chromatography-Olfactometry, Quantitative Measurements, Aroma Recombination, and Omission Tests.

The key aroma compounds of Chinese Vidal icewine were characterized by means of gas chromatography-olfactometry (GC-O) coupled with mass spectrometry (MS) on polar and nonpolar columns, and their flavor dilution (FD) factors were determined by aroma extract dilution analysis (AEDA). A total of 59 odor-active aroma compounds in three ranks of Vidal icewines were identified, and 28 odorants (FD ≥ 9) were further quantitated for aroma reconstitution and omission tests. ß-Damascenone showed the highest FD value of 2187 in all icewines. Methional and furaneol were first observed as important odorants in Vidal icewine. Aroma recombination experiments revealed a good similarity containing the 28 important aromas. Omission tests corroborated the significant contribution of ß-damascenone and the entire group of esters. Besides, 4-hydroxy-2,5-dimethyl-3(2H)-furanone (furaneol) and 3-(methylthio)-1-propanal (methional) also had significant effects on icewine character, especially on apricot, caramel, and tropical fruit characteristics.

Characterisation of aroma profiles of commercial sufus by odour activity value, gas chromatography-olfactometry, aroma recombination and omission studies.

Sufu is a solid-state fermented product made from soya beans. For the sake of quality control and regulation purposes, it is essential to be able to identify key odorants of various commercial sufus. To identify the aroma-active compounds in sufus, gas chromatography-olfactometry/aroma extract dilution analysis (GC-O/AEDA) was performed, and odour activity value (OAV) was estimated. The correlations between aroma profiles and identified aroma-active compounds were also investigated by principal component analysis. Results showed that 35 aroma-active compounds were detected through OAV calculation, while 28 compounds were identified by using GC-O/AEDA. Quantitative descriptive analysis revealed that aroma recombination model based on OAV calculation was more similar to original sufu in terms of aroma comparing to aroma recombination model based on GC-O/AEDA. Omission experiments further confirmed that the aroma compounds, such as ethyl butanoate, ethyl 2-methylbutanoate, ethyl hexanoate, (E,E)-2,4-decadienal and 2,6-dimethylpyrazine, contributed most significantly to the characteristic aroma of a commercial sufu.