Characterization of the key aroma compounds in Semnostachya menglaensis Tsui by gas chromatography-olfactometry, odor activity values, aroma recombination, and omission analysis

Analysis of composition and source of the key aroma compounds in stir-fried pepper tallow

Stir-fried pepper tallow is widely used in cooking due to its special flavor, particularly in hot-pot dishes. However, the composition and source of the key aroma compounds in stir-fried pepper tallow are poorly understood, resulting in uneven quality. Here, the key aroma compounds were screened using flavor dilution factors (FD) and odor activity values (OAVs). A total of 41 odorants compounds were identified. Of these, 20 compounds with FD ≥ 8 were aroma-active compounds. Furthermore, among these 20 compounds, 15 with OAVs ≥ 1were the key aroma-active compounds and most of these (13 out of 15 odorants) were produced from pepper. Glycosides in pepper are the precursors of the most of these key aroma compounds. It may be possible to improve the flavor quality of stir-fried pepper tallow by hydrolyzing glycosides. These findings should help to establish a standard to assess and improve the quality of stir-fried pepper tallow.

Unraveling volatilomics profiles of milk products from diverse regions in China

To distinguish Chinese milks from different regions, 13 milk samples were gathered from 13 regions of China in this study: Inner Mongolia (IM), Xinjiang (XJ), Hebei (HB), Shanghai (SH), Beijing (BJ), Sichuan (SC), Ningxia (NX), Henan (HN), Tianjin (TJ), Qinghai (QH), Yunnan (YN), Guangxi (GX), and Tibet (XZ). Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) combined with the electronic nose (E-nose) technology, was used to detect and analyze the volatile compounds in these milk samples. The qualitative and quantitative results identified 29 volatile chemicals, and we established a database of flavor profiles for the main milk-producing regions in China. E-nose analysis revealed variations in the odor of milk across different areas. Furthermore, results from partial least squares discriminant analysis (PLS-DA) and odor activity values (OAVs) suggested that seven volatile compounds: decane, 2-heptanone, 2-undecanone, 2-nonanone, 1-hexadecanol, 1-octen-3-ol, and (E)-2-nonenal, could be considered as key flavor compounds in Chinese milk products.

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.

Exploring aromatic components differences and composition regularity of 5 kinds of these 4 aroma types Phoenix Dancong tea based on GC-MS

Different aromatic components do indeed give different tea flavors. There is still little research on whether there is a certain regularity in the combination and content of aromatic components in different aroma types of Phoenix Dancong (PDC) tea. This potential regularity may be a key factor in unraveling the relationship between reproduction and evolution in PDC tea. Here, the 5 kinds of these 4 aroma types PDC tea (Zhuye, Tuofu, Jianghuaxiang, Juduo, Yashixiang) were used as research materials in this study, the headspace solid-phase microextraction combined with gas chromatography-mass spectrometry was used to analyze the aromatic components of these PDC teas. The results showed a total of 36 aromatic components identified in this study. When conducting cluster analysis, it was found that similarity degree arrangement sequence of 5 PDC teas was Juduo, Tuofu, Yashixiang, Zhuye and Jianghuaxiang. Among these aromatic components, the 7,9-Di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione, the 2-Cyclopenten-1-one, 3-methyl-2-(2-pentenyl)-,(Z)-, the 2,4-Di-tert-butylphenol, the 3,7-dimethyl-1,5,7-Octatrien-3-ol, and the 2-Furanmethanol,5-ethenyltetrahydro-.alpha.,.alpha.,5-trimethyl-,cis- are common to 5 PDC teas. This study aims to elucidate the similarities in the aromatic components of 5 PDC teas, revealing the major aroma-endowed substances of various aroma, and providing theoretical reference for further exploring the relationship between aroma type discrimination, variety selection, and evolution of PDC teas.

Characterization of the Aroma Profiles of Guangdong Black Teas Using Non-Targeted Metabolomics

Guangdong black teas have diverse flavors and aromas. To explore the molecular basis of these aromas, we extracted and analyzed the volatile flavor compounds of 31 black tea samples from 7 districts (Yingde, Luokeng, Renhua, Meizhou, Chaozhou, Lianshan, and Heyuan) in Guangdong Province with headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). Then, 135 volatile flavor compounds (VFCs) were identified and grouped into 12 classes according to their chemical structure. Notably, alcohols accounted for 31.40-44.43% of total VFCs. The score plot of supervised partial least squares-discriminant analysis (PLS-DA) revealed good discrimination for most black tea samples. Additionally, 64 compounds with variable importance in projection > 1.0 were identified as differential odorants. Through an odor activity value analysis, eight volatile compounds were identified as the key active differential VFCs: linalool, methyl salicylate, phenylethyl alcohol, p-cresol, 3-methyl-butanoic acid, geraniol, benzaldehyde, and benzeneacetaldehyde. Thus, benzeneacetaldehyde and linalool in YJ-Yingde samples, benzaldehyde in Luokeng samples with an almond-like aroma, phenylethyl alcohol in the Heyuan samples, and p-cresol and 3-methyl-butanoic acid in the Chaozhou samples were the key volatile flavor compounds that could differentiate local black teas from other black teas. These findings will enrich the research in tea aroma chemistry and provide a method for identifying the origins of Guangdong black teas.

Flavor production in fermented chayote inoculated with lactic acid bacteria strains: Genomics and metabolomics based analysis

In this study, genomics and metabolomics were combined to reveal possible bio-synthetic pathways of core flavor compounds in pickled chayote via lactic acid bacteria (LAB) fermentation. The Lactiplantibacillus plantarum, Levilactobacillus brevis, and Lacticaseibacillus paracasei were selected as core LAB strains with better flavor-producing ability for chayote fermentation. The genomic results showed L. plantarum contained the largest number of metabolism annotated genes, while L. brevis had the fewest. Besides, the largest number of volatile compounds was detected in chayote fermented by L. plantarum, followed by L. brevis and L. paracasei. Some unique odor-active compounds (aldehydes, esters, and alcohols) and taste-active compounds (amino acids and dipeptides) were produced by different LAB strains. Accordingly, phenylalanine metabolic pathway (M00360), amino acid metabolic decomposition pathway (the Ehrlich pathway) and the anabolic pathway (the Harris pathway), and fatty acid biosynthesis pathway (M00061) were the main biosynthesis pathway involved in the flavor formation via LAB fermentation.

Characterization of Key Odor-Active Compounds in Sun-Dried Black Tea by Sensory and Instrumental-Directed Flavor Analysis

The aroma profile of sun-dried black tea (SBT) was identified by headspace solid–phase microextraction (HS–SPME) coupled with gas chromatography–mass spectrometry (GC–MS) and gas chromatography–olfactometry (GC–O). A total of 37 scents were captured by using the GC–O technique, and 35 scents with odor intensities ranging from 1.09 ± 1.93 to 9.91 ± 0.29 were identified. Twenty-one compounds were further identified as key odor-active compounds with odor activity values (OAVs) greater than or equal to one. These key odor-active compounds were restructured with their detected concentrations, and the aroma profile of the selected SBT sample was successfully imitated to a certain extent. An omission test was performed by designing 25 models and confirmed that (E)-β-damascenone, β-ionone, dihydro-β-ionone, linalool, and geraniol were the key odor-active compounds for the aroma profile of SBT. Meanwhile, phenylethyl alcohol, (E)-2-decenal, hexanal, and methyl salicylate were also important to the aroma profile of SBT. This study can provide theoretical support for the improvement of the aroma quality of sun-dried black tea.

Identification and confirmation of key compounds causing cooked off-flavor in heat-treated tomato juice

Cooked off-flavor produced by heat treatment greatly limited the acceptability of commercial tomato juice. To screen and identify the cooked off-flavor compounds, gas chromatography-mass spectrometry-olfactometry (GC-MS-O), aroma extract dilution analysis (AEDA), gas chromatography-mass spectrometry (GC-MS), and odor activity value (OAV) calculation were applied simultaneously. The results showed that there were 17 aroma-active compounds in tomato juice samples. Among them, three newly formed sulfur-containing compounds (dimethyl sulfide, dimethyl trisulfide, and methional) and 1-octen-3-one, which exhibited cooked corn/potato, onion, and mushroom odor, were proved to be responsible for the cooked off-flavor in heat-treated tomato juice (HTJ) by omission experiments and electronic nose analysis. The three newly formed sulfur-containing compounds were further confirmed to be the key compounds responsible for the cooked off-flavor in four different tomato cultivars that were commonly consumed in the market. PRACTICAL APPLICATION: Tomato is one of the most popular vegetables in the world and tomato juice is an important part of the tomato industry. However, the cooked off-flavor of tomato juice after sterilization severely restricts its industrial development. This study analyzed and compared the changes of aroma compounds before and after sterilization, and identified and confirmed the major off-flavor components. This work could provide fundamental information for the prevention of cooked off-flavor.

Characterization of key aroma compounds in stewed mutton (goat meat) added with thyme (Thymus vulgaris L.) based on the combination of instrumental analysis and sensory verification

Thyme (Thymus vulgaris L.) is widely used as a traditional spice in the cooking of goat meat (mutton) due to its distinctive flavor and the ability to weaken the "goaty flavor". To investigate the aroma characteristics of stewed mutton with thyme (SMT), four SMT samples prepared using different cooking utensils were analyzed by gas chromatography-mass spectrometry/olfactometry (GC-MS/O). Totally, 26 aroma-active compounds (AACs) were determined by GC-MS/O and further quantified. Among these, 20 AACs exhibited odor activity values (OAV) greater than 1. However, no significant differences existed among the four SMTs, which indicated that different utensils had little effect on the aroma profile of SMTs. Aroma recombination and omission experiments results showed that nonanal, (E)-2-octenal, and (E,E)-2,4-decadienal had the greatest contribution to the aroma profile of SMTs. These three compounds, together with dimethyl trisulfide, 3-methyl-butanal, octanal, (E)-2-decenal, (E)-2-nonenal, methanethiol, hexanal, (E)-2-undecenal, and 1-octen-3-ol, were confirmed as the key aroma compounds in SMTs.

Characterization of aroma and bacteria profiles of Sichuan industrial paocai by HS-SPME-GC-O-MS and 16S rRNA amplicon sequencing

Sichuan industrial paocai and traditional home-made paocai have different aroma profiles due to different manufacturing techniques, but detailed information about the aroma profiles and aroma-producing microorganism of Sichuan industrial paocai remain largely elusive. For this reason, we established and validated an external standard method of headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) combined with gas chromatography-olfactometry (GC-O) for identification and accurate quantitation of aroma-active compounds in Sichuan industrial paocai. This method was combined with 16S rRNA amplicon sequencing to comprehensively analyze the aroma and bacteria profiles of Sichuan industrial paocai. A total of 121 volatile compounds were identified, among which 36 odorants were identified as aroma-active compounds with aroma intensities (AIs) ranging from 0.67 to 5.00 by GC-O. The types of aroma-active compounds in Sichuan industrial paocai were variety-specific to some extent, but the aroma-active compounds shared by different varieties of Sichuan industrial paocai (i.e., skeleton aroma-active compounds) were phenylethyl alcohol, acetic acid, butanoic acid, 2-methylbutanoic acid, ethyl hexanoate, 4-ethylphenol and 4-ethylguaiacol. Moreover, 17 key aroma-active compounds of AI > 1 in radish paocai were quantitated by external standard method, and their odor activity values (OAVs) were calculated based on the odor thresholds. Further, 12 aroma-active compounds with OAV ≥ 1 in one of the radish paocai were selected to construct the recombination model, which revealed good agreement with the original sample. Furthermore, Lactobacillus, Pediococcus, Pseudomonas and Sphingomonas were the dominant bacteria in Sichuan industrial paocai. Correlation analysis between 16 dominant bacteria and 36 aroma-active compounds showed that Pediococcus, Arcobacter and Lactobacillus could be the core aroma-producing bacteria of Sichuan industrial paocai.

Characterization of key aroma compounds in flat peach juice based on gas chromatography-mass spectrometry-olfactometry (GC-MS-O), odor activity value (OAV), aroma recombination, and omission experiments

The aroma profiles of fresh flat peach juice (FPJ) samples obtained from four different cultivars (RP1), (ZLP), (RP18), and (ZP) were characterized by gas chromatography-Mass spectrometry-olfactometry (GC-MS-O). Totally, 32 aroma-active compounds in FPJs were identified by GC-MS-O and further quantified. Of these, 14 aroma-active compounds presented odor activity values (OAVs) greater than 1, with several lactones and aldehydes contributing as key aroma-active components of FPJs. Partial least-squares regression (PLSR) revealed that RP18 was greatly related to "fruity", "sweet" and "peach-like" attributes, while ZLP was highly correlated with "floral" and "green and grassy" attributes, confirming the quantitative describe analysis (QDA) results. In addition, an aroma recombination experiment was conducted to mimic the aroma profile of flat peach juice based on the actual concentrations of RP18. Omission experiments indicated that lactones were very highly significant for the characteristic aroma of FPJ.

Enzymatic hydrolysis and auto-isomerization during β-glucosidase treatment improve the aroma of instant white tea infusion

The aroma changes in instant white tea resulting from β-glucosidase treatment was investigated by quantitative descriptive analysis (QDA), gas chromatography-mass spectrometry (GC-MS), odour activity value analysis (OAV), aroma reconstruction and omission tests. The grassy, floral and sweet notes increased significantly (P < 0.05), and the roasted note decreased significantly (P < 0.05) upon β-glucosidase treatment. Quantitative analysis showed that the concentrations of benzaldehyde, benzeneacetaldehyde, (Z)-3-hexen-1-ol, linalool, phenylethyl alcohol, cis-linalool oxide, trans-linalool oxide, hexanol, hotrienol and (E)-2-hexen-1-ol increased significantly (P < 0.05) after treatment; however, (Z)-3-hexen-1-ol isomerized to (E)-2-hexen-1-ol. OAV analysis, aroma reconstruction and the omission test showed that the grassy, floral and sweet notes increased as the (Z)-3-hexen-1-ol, cis/trans-linalool oxide and benzeneacetaldehyde increased, whereas the roasted note declined under the same conditions. The enzymatic hydrolysis of glycosidic precursors and the auto-isomerization of volatile compounds provide new information for understanding how β-glucosidase treatment improves the aroma of tea products.