Characterization of the key aroma compounds in Laoshan green teas by application of odour activity value (OAV), gas chromatography-mass spectrometry-olfactometry (GC-MS-O) and comprehensive two-dimensional gas chromatography mass spectrometry (GC × GC-qMS)

Characterization of the key aroma compounds in different varieties of hops by application of the Sensomics approach

Aroma is a crucial indicator of hop quality. This study analyzed the differences in aroma compound composition among six hop varieties from three regions: North America, Europe, and Asia. Descriptive analysis and sensomic approaches including gas chromatography-olfactometry/aroma extract dilution analysis, odour activity value calculation and aroma recombination were used for the detailed characterization and comparative analysis of hop aroma. A total of 55 aroma-active compounds were identified. Among them, linalool, geraniol, β-myrcene, 2-undecanone, and methyl decanoate contributed significantly to hop aroma. Orthogonal partial least squares discriminant analysis revealed that, except for the SAAZ and XinYuan hops with some similarities in their aroma composition, the remaining hops exhibited unique aroma characteristics. A total of 16 compounds, including methyl 5-methylhexanoate and (E)-β-farnesene, were identified as differentiating aroma compounds in the six hop samples. This study enriches the knowledge on hop flavour with different origins and provides valuable insights into its application.

Uncovering the Shuixian tea grades hierarchy in Chinese national standard: From sensory evaluation to microstructure and volatile compounds analysis

Basic standard samples are integral for ensuring consistency and quality control of tea. Understanding the real reasons behind the hierarchical system of Shuixian tea grades in the Chinese national standard is crucial to the scientific development of tea standardization. In this investigation, different grade samples of Shuixian tea strictly conformed to the Chinese national standard, serving as the research objects. Sensory evaluation, SEM and HS-SPME-GC-MS were employed to comprehensively analyze the aroma characteristics. The odor profiles of special grade samples predominantly featured floral and fruity aromas, which attributed to compounds such as geraniol, indole, phenylethyl alcohol. Additionally, hexanal, (E)-3-hexen-1-ol and other compounds contributed to fruity and sweet aroma in first grade. Notably, the predominant roasted and sweet aromas of second grade were attributed to compounds including pyridine, 2,5-dimethyl-pyrazine. This study lays a solid foundation for the scientific development of Chinese national standards and international standard system.

Sensomics-assisted analysis unravels the formation of the Fungus Aroma of Fu Brick Tea

Fu Brick Tea (FBT) is characterized by Fungus Aroma (FA), which determines the quality of FBT products. However, the aroma constituents and their interactive mechanism for FA remain unclear. In this study, the FBT sample with the optimal FA characteristics was selected from 29 FBTs. Then, 19 components with OAV ≥ 1 were identified as the odorants involved in the FA formation. The aroma recombination test suggested that the FA was potentially produced by the synergistic interplay among the 15 key odorants, including (E,E)-2,4-heptadienal, (E,E)-2,4-nonadienal, (E)-2-nonenal, (E,Z)-2,6-nonadienal, (E)-2-octenal, (E)-β-ionone, 4-ketoisophorone, dihydroactinidiolide, (E)-β-damascenone, 1-octen-3-ol, linalool, geraniol, heptanal, hexanal, and phenylacetaldehyde. And, the synergistic effects between them were preliminarily studied by aroma omissions, such as modulatory effects, masking effects, compensatory effects, and novelty effects, ultimately contributing to the FA. In all, this work helps us better understand the formation of the FA and provides a basis for the improvement of FBT production technology.

Changes in volatile flavors during the fermentation of tomato (Solanum lycopersicum L.) juice and its storage stabilization

Flavor is a crucial indicators of the quality of fermented tomato juice; however, there has been limited research in this area. Herein, headspace solid-phase microextraction gas chromatography-mass spectrometry was used to analyze the volatile metabolites at different stages during FTJ fermentation. 131 volatile organic compounds (VOCs) were identified, with alcohols, acids, and esters as the main compounds. The content of superoxide dismutase (SOD) and lycopene (LYC) had a positive correlation with methyl salicylate, ethyl acetate, and linalyl acetate. Subsequently, the storage stability of FTJ was evaluated at temperatures of 4 °C, 25 °C, and 37 °C over a period of 45 d, revealing that the quality of FTJ decreased with increasing storage temperature. The shelf life of FTJ under different storage conditions was determined using SOD activity and LYC content as quality indicators. The final shelf life was 47 d at 37 °C, 69 d at 25 °C, and 123 d at 4 °C.

Comparison of Volatile Compounds in Jingshan Green Tea Scented with Different Flowers Using GC-IMS and GC-MS Analyses

Scented green tea (Camellia sinensis) is a type of reprocessed green tea produced by scenting with flowers. To investigate the differences in the volatiles of scented green tea processed with four different flowers (Jasminum sambac, Osmanthus fragrans, Michelia alba, and Rosa rugosa), gas chromatography-ion mobility spectrometry (GC-IMS) and gas chromatography-mass spectrometry (GC-MS) were employed to detect and identify the volatile compounds in the four types of scented teas. GC-IMS and GC-MS identified 108 and 101 volatile compounds, respectively. The key characteristic volatile compounds, namely indole, linalool, β-myrcene, benzyl acetate, and ethyl benzoate (jasmine tea); cedrol, (E)-β-ionone, γ-decalactone, and dihydro-β-ionol (osmanthus tea); geraniol, phenylethyl alcohol, jasmone, methyl jasmonate, hexadecanoic acid, 4-ethyl-benzaldehyde, 2-methylbutyl hexanoate, and indole (michelia tea); and 3,5-dimethoxytoluene, (E)-β-ionone, and 2-methylbutyl hexanoate (rose tea), were identified through chemometric analysis combined with relative odor activity values (ROAVs) and sensory evaluation. This study provides new insights into the formation of aroma molecular fingerprints during green tea scenting with flowers, providing theoretical guidance for infusing distinct aroma characteristics into green tea during scented tea processing.

Phytochemical and Flavor Characteristics of Mulberry Juice Fermented with Lactiplantibacillus plantarum BXM2

Fermentation of mulberry juice not only improves its shelf life, but also effectively enhances their flavor and nutritional quality. This study elucidated the phytochemical and flavor characteristics of mulberry juice fermented with Lactiplantibacillus plantarum BXM2, originally isolated from naturally fermented fruit beverage, through widely targeted metabolomics. The fermentation produced the unique flavor of fermented juice and decreased the pH from 4.15 to 3.19. The metabolomic analysis detected 907 non-volatile metabolites, from which 359 significantly different non-volatile metabolites (up 238, down 121) were screened out. Among 731 identified volatile metabolites, 26 flavor substances were the major contributors to the flavor differences between fermented and unfermented mulberry juices. It is hypothesized that lipid metabolism and amino acid catabolism are crucial pathways for the flavor enhancement of mulberry juice fermented with L. plantarum BXM2. Meanwhile, significant increases of the contents of a variety of bioactive substances, such as indole-3-lactic acid, octadeca-9,12,15-trienoic acid, di-/tri-peptides, etc., conferred additional health potential to BXM2-fermented mulberry juice.

Characteristics of saltiness-enhancing peptides derived from yeast proteins and elucidation of their mechanism of action by molecular docking

This study aimed to identify saltiness-enhancing peptides from yeast protein and elucidate their mechanisms by molecular docking. Yeast protein hydrolysates with optimal saltiness-enhancing effects were prepared under conditions determined using an orthogonal test. Ten saltiness-enhancing peptide candidates were screened using an integrated virtual screening strategy. Sensory evaluation demonstrated that these peptides exhibited diverse taste characteristics (detection thresholds: 0.13-0.50 mmol/L). Peptides NKF, LGLR, WDL, NMKF, FDSL and FDGK synergistically or additively enhanced the saltiness of a 0.30% NaCl solution. Molecular docking revealed that these peptides predominantly interacted with TMC4 by hydrogen bonding, with hydrophilic amino acids from both peptides and TMC4 playing a pivotal role in their binding. Furthermore, Leu217, Gln377, Glu378, Pro474 and Cys475 were postulated as the key binding sites of TMC4. These findings establish a robust theoretical foundation for salt reduction strategies in food and provide novel insights into the potential applications of yeast proteins.

Variation in the Aroma Composition of Jasmine Tea with Storage Duration

This study investigated the changes in the aroma of jasmine tea during storage. Solid-phase micro-extraction (SPME)-gas chromatography (GC)-mass spectrometry (MS) and stir bar sorptive extraction (SBSE)-GC-MS were combined to detect all volatile compounds. GC-olfactometry (GC-O), odor activity value (OAV), and p-value were employed to analyze and identify the key aroma compounds in six jasmine tea samples stored for different durations. Nine key aroma compounds were discovered, namely (Z)-3-hexen-1-yl acetate, methyl anthranilate, methyl salicylate, trans-β-ionone, linalool, geraniol, (Z)-4-heptenal, benzoic acid methyl ester, and benzoic acid ethyl ester. The importance of these compounds was confirmed through the aroma addition experiment. Correlation analysis showed that (Z)-4-heptenal might be the main reason for the increase in the stale aroma of jasmine tea. Through sensory evaluation and specific experimental analysis, it can be concluded that jasmine tea had the best aroma after 3 years of storage, and too long a storage time may cause the overall aroma of the tea to weaken and produce an undesirable odor. The findings can provide a reference for the change in aroma during the storage of jasmine tea and provide the best storage time (3 years) in terms of jasmine tea aroma.

Effects of Loquat Juice Addition on Sensory Characteristics and Volatile Organic Compounds of Loquat Beer

Beer, as an ancient and widely consumed alcoholic beverage, holds a rich cultural heritage and history. In recent years, fruit beer has gained significant attention as a distinct beer type produced by incorporating fruit juice into traditional beer ingredients. This study employed headspace solid-phase microextraction-gas chromatography-mass spectrometry techniques, redundancy analysis, and orthogonal projections to latent structures discriminant analysis to analyze the sensory evaluation, physicochemical properties, organic acids, and volatile organic compounds (VOCs) of loquat beer with different proportions of loquat juice. The results shown that the addition of an appropriate amount of loquat juice (40%) enhanced the overall sensory quality of the beer; as the proportion of loquat juice increased, the contents of malic acid and tartaric acid significantly increased (p < 0.05). A total of 100 VOCs were identified, among which 23 key VOCs (VIP > 1, p < 0.05) represented the most important characteristic flavor components in loquat beer based on their odor activity value (OAV). This study holds significant importance for the value-added processing and economic development of loquat.

Ultrasound-induced modifications of beef flavor characteristics during postmortem aging

To investigate the effect of ultrasound treatment on the flavor profile of beef during postmortem aging, a comprehensive analysis of beef flavor was conducted at 0, 7, and 12 d of aging using sensory evaluation and electronic nose. Furthermore, the key volatile flavor compounds were identified using gas chromatography-mass spectrometry (GC-MS), and the odor activity value (OAV) was further evaluated. In addition, the primary pathway involved in flavor formation during beef aging after ultrasound treatment was explored. The results indicated that ultrasound enhanced the flavor profile of beef during postmortem aging by modifying the OAV of hexanal, heptanal, octanal, nonanal, decanal, (Z)-2-nonenal, dodecanal, pentanal, 1-octen-3-ol, octanoic acid, and 2-pentylfuran. Lipid oxidation was a crucial pathway through which ultrasound promoted the generation of volatile flavor compounds in beef, confirmed by the improved oxidation level of fatty acids, particularly monounsaturated ones. The study indicates that ultrasound technology can be regarded as an effective method for enhancing the beef flavor profile during postmortem aging.

Effects of processing methods on the aroma of Poria cocos and its changing regulations during processing

Poria cocos is a natural source of fungal food raw materials. Processing method is a key effecting the aroma of Poria cocos. In this study, the aroma compounds of Poria cocos products processed using sweating-low-temperature drying (SW-LD), sweating-high-temperature drying (SW-HD), steaming-low-temperature drying (ST-LD), and steaming-high-temperature drying (ST-HD) were compared by headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS), and the changes in aroma compounds of Poria cocos products during processing were analyzed. GC-MS analysis showed SW-HD product had highest content of aroma compounds. Aroma activity value (OAV) analysis indicated that 9 aroma compounds contributed to the overall aroma of Poria cocos. Among 9 compounds of Poria cocos, 1-octen-3-ol, hexanal, nonanal, octanal, trans-2-octenal, and heptanal contributed to mushroom, refreshing, sweet and fatty characters. In addition, the aroma compound changes during the processing were analyzed, revealing that steaming and sweating were the key processes affecting the aroma of Poria cocos products. The findings of this study provide valuable theoretical guidance for the development of Poria cocos processing technology.

The Light-Intensity-Affected Aroma Components of Green Tea during Leaf Spreading

Leaf spreading is a key processing step that affects the aroma formation of green tea. The effects of a single-light wavelength on the aroma and taste of tea have been extensively studied. Less attention has been paid to the effect of different complex light intensities on the formation of green tea's volatile aroma during leaf spreading. The current study was designed to evaluate how leaf spreading under different complex light intensities relates to the quality of green tea. Using headspace solid-phase micro-extraction and gas chromatography-mass spectrometry (HS-SPME/GC-MS), volatile flavor compounds in green tea were analyzed during leaf spreading in five different light conditions. Multivariate statistical analysis and odor activity values (OAVs) were used to classify these samples and identify key odors. Eight distinct groups, including ninety volatile compounds, were detected. The most prevalent volatile compounds found in green tea samples were hydrocarbons and alcohols, which accounted for 29% and 22% of the total volatile compounds, respectively. Fourteen volatile compounds (OAV > 1) were identified as key active differential odorants. The chestnut-like aroma in green tea was mostly derived from 3-methyl-butanal and linalool, which were significantly accumulated in medium-intensity light (ML).

Volatolomics-assisted characterization of the key odorants in green off-flavor black tea and their dynamic changes during processing

Aroma plays a pivotal role in the quality of black tea. However, the acceptability of black tea is greatly limited by the green off-flavor (GOF) resulting from the inappropriate processing control. In this study, the key odorants causing GOF were investigated by volatolomics, and their dynamic changes and formation pathways were in-depth understood. Significant alterations in volatile metabolites were observed in the withering stage. A total of 14 key odorants were identified as contributors to GOF, including 2-methylpropanal, 3-methylbutanal, 1-hexanol, nonanal, (E, E)-2,4-heptadienal, benzaldehyde, linalool, (E, E)-3,5-octadiene-2-one, β-cyclocitral, phenylacetaldehyde, (E, E)-2,4-nonadienal, methyl salicylate, geraniol, and β-ionone. Among them, (E, E)-2,4-heptadienal (OAV = 3913), characterized by fatty, green, and oily aromas, was considered to be the most important contributor causing GOF. Moreover, it was found that lipid degradation served as the primary metabolic pathway for GOF. This study provides a theoretical foundation for off-flavor control and quality improvement of black tea.

GC-MS Combined with Proteomic Analysis of Volatile Compounds and Formation Mechanisms in Green Teas with Different Aroma Types

Aroma is one of the key factors for evaluating the quality of green tea. A tender aroma (NX) and floral-like aroma (HX) are two types of high-quality aroma of green tea. In this work, the different aroma types of baked green tea were classified by sensory evaluation. Then, seven tea samples with a typical tender or floral-like aroma were selected for further volatile component analysis by GC-MS. A total of 43 aroma compounds were identified in two different aroma types of baked green tea samples. The PCA showed that linalool, geraniol, 3-hexenyl butyrate, and 3-hexenyl hexanoate were the major volatiles contributing to the HX. On the other hand, most of the alcohol volatiles, such as 1-octanol, 1-octen-3-ol, 1-dodecanol, 1-hexadecanol, phenylethyl alcohol, benzyl alcohol, aldehydes and some hydrocarbons contributed more to the NX. In addition, the chemical composition analysis showed that the content of free amino acids was higher in NX green tea samples, while the content of catechins was relatively higher in HX tea samples. A proteomic analysis revealed that most of the enzymes involved in VPBs pathways, such as phenylalanine ammonialyase, peroxidase, and shikimate-O-hydroxycinnamoyl transferase, were more abundant in NX than in HX tea samples. These results laid a foundation for the aroma formation mechanism of different aroma types of baked green tea and provided some theoretical guidance for the breeding of specific aroma varieties.

The Effects of Nitrogen Fertilizer on the Aroma of Fresh Tea Leaves from Camellia sinensis cv. Jin Xuan in Summer and Autumn

Nitrogen fertilization level and harvesting season significantly impact tea aroma quality. In this study, we analyzed the volatile organic compounds of fresh Jin Xuan (JX) tea leaves under different nitrogen application levels (N0, N150, N300, N450) during summer and autumn. A total of 49 volatile components were identified by gas chromatography-mass spectrometry (GC-MS). Notably, (E)-2-hexenal, linalool, and geraniol were the main contributors to the aroma of fresh JX leaves. The no-nitrogen treatment (N0) presented the greatest quantity and variety of volatiles in both seasons. A greater difference in volatile compounds was observed between nitrogen treatments in summer vs. autumn. The N0 treatment had a greater total volatile concentration in summer, while the opposite was observed in the nitrogen application treatments (N150, N300, N450). Summer treatments appeared best suited to black tea production. The concentration of herbaceous aroma-type volatiles was higher in summer, while the concentration of floral volatiles was higher in autumn. Volatile concentrations were highest in the N0 and N450 treatments in autumn and appeared suitable for making black tea and oolong tea. Overall, this research provides valuable insights into how variations in N application rates across different harvesting seasons impact the aroma characteristics of tea leaves.

Aroma and taste analysis of pickled tea from spontaneous and yeast-enhanced fermentation by mass spectrometry and sensory evaluation

Anaerobically fermented pickled tea (PT) can be produced by spontaneous fermentation (SF) or yeast-enhanced fermentation (YF). Aroma and taste characteristics of PT during YF and SF were investigated using sensory evaluation, odour activity, aroma character impact values, HS-SPME-GC-MS, UPLC-QQQ-MS/MS, and spectrophotometry, annotating 198 volatile and 115 non-volatile components. The main contributing volatile components were β-ionone, and 1-octanol, promoted by YF and SF, and yielding floral and fruity aromas respectively. Additionally, compared with SF, YF promoted the formation of citronellol yielding a floral aroma, inhibited the stale aroma of methoxybenzenes, and reduced bitter, astringent, and sour tastes. Furthermore, partial least-squares regression analysis identified the main components related to the 'acides aroma' of PT as linalool oxide, n-decanoic acid, hexanoic acid, 3,7-dimethyl-2,6-octadienoic acid, 3-methyl-1-dodecyn-3-ol, and nerolidol. This application could be used as methodology for the comprehensive analysis of tea aroma and taste and these results can act as guidelines for PT production and quality control.

Unraveling the contributing factors of stale odor in Longjing tea through a sensomics approach

Longjing tea is renowned for its fresh aroma and high value. However, during storage, the emergence of an off-flavor known as "stale odor" can significantly impact the flavor quality and economic benefits of Longjing tea. Yet, the specific volatiles responsible for this stale odor in Longjing tea remain unknown. In this study, Longjing tea samples with varying degrees of stale odor intensity were analyzed using simultaneous distillation extraction coupled with gas chromatography-mass spectrometry (SDE-GC-MS). Through odor activity value (OAV) and fractional omission testing, hexanoic acid and trans-2-nonenal were identified as the primary contributors to the stale odor. Moreover, the concentration of hexanoic acid was found to be valuable in predicting the intensity of the stale odor in Longjing tea. The oxidative degradation of linoleic acid was proved as the generation pathway of stale odor in Longjing tea. These findings provide essential theoretical principles for Longjing tea production and preservation.

The key aroma components of steamed green tea decoded by sensomics and their changes under different withering degree

Steamed green tea has a long history and unique aroma, but little is known about its key aroma components. In this study, 173 volatiles in steamed green tea were identified using solvent-assisted flavor evaporation and headspace-solid phase microextraction plus two chromatographic columns of different polarities. Aroma extract dilution analysis revealed 48 highly aroma-active compounds with flavor dilution factors 64-1024. Internal standards were used to calculate odorant active value (OAV), and 11 OAV > 1 key aroma compounds were determined. Omission test identified eight substances, including dimethyl sulfide, (E)-β-ionone, cis-jasmone, linalool, nonanal, heptanal, isovaleraldehyde and (Z)-3-hexenol, as the key aroma active compounds of steamed green tea. With the increase of withering degree, the content of these substances increased first and then decreased except for heptanal and cis-jasmone. Moreover, the water content of 62 % was suggested to be an appropriate withering degree during the processing of steamed green tea.

Enhancing Odor Analysis with Gas Chromatography-Olfactometry (GC-O): Recent Breakthroughs and Challenges

Gas chromatography-olfactometry (GC-O) has made significant advancements in recent years, with breakthroughs in its applications and the identification of its limitations. This technology is widely used for analyzing complex odor patterns. The review begins by explaining the principles of GC-O, including sample preparation, separation methods, and olfactory evaluation techniques. It then explores the diverse range of applications where GC-O has found success, such as food and beverage industries, environmental monitoring, perfume and aroma development, and forensic analysis. One of the major breakthroughs in GC-O analysis is the improvement in separation power and resolution of odorants. Techniques like rapid GC, comprehensive two-dimensional GC, and multidimensional GC have enhanced the identification and quantification of odor-active chemicals. However, GC-O also has limitations. These include the challenges in detecting and quantifying trace odorants, dealing with matrix effects, and ensuring the repeatability and consistency of results across laboratories. The review examines these limitations closely and discusses potential solutions and future directions for improvement in GC-O analysis. Overall, this review presents a comprehensive overview of the recent advances in GC-O, covering breakthroughs, applications, and limitations. It aims to promote the wider usage of GC-O analysis in odor analysis and related industries. Researchers, practitioners, and anyone interested in leveraging the capabilities of GC-O in analyzing complex odor patterns will find this review a valuable resource. The article highlights the potential of GC-O and encourages further research and development in the field.

GC-IMS-Based Volatile Characteristic Analysis of Hypsizygus marmoreus Dried by Different Methods

Gas chromatography-ion mobility spectroscopy (GC-IMS) was used to analyze the volatile components in dried Hypsizygus marmoreus of different drying methods, including hot air drying (HAD), heat pump drying (HPD), heated freeze-drying (HFD), and unheated freeze-drying (UFD). A total of 116 signal peaks corresponding to 96 volatile compounds were identified, including 25 esters, 24 aldehydes, 23 alcohols, 13 ketones, 10 heterocyclic compounds, 8 carboxylic acids, 7 terpenes, 3 sulfur-containing compounds, 2 nitrogen-containing compounds, and 1 aromatic hydrocarbon. The total content of volatile compounds in H. marmoreus dried by the four methods, from highest to lowest, was as follows: HAD, HPD, HFD, and UFD. The main volatile compounds included carboxylic acids, alcohols, esters, and aldehydes. Comparing the peak intensities of volatile compounds in dried H. marmoreus using different drying methods, it was found that the synthesis of esters, aldehydes, and terpenes increased under hot drying methods such as HAD and HPD, while the synthesis of compounds containing sulfur and nitrogen increased under freeze-drying methods such as HFD and UFD. Nine common key characteristic flavor compounds of dried H. marmoreus were screened using relative odor activity values (ROAV > 1), including ethyl 3-methylbutanoate, acetic acid, 2-methylbutanal, propanal, methyl 2-propenyl sulfate, trimethylamine, 3-octanone, acetaldehide, and thiophene. In the odor description of volatile compounds with ROAV > 0.1, it was found that important flavor components such as trimethylamine, 3-octanone, (E)-2-octenal, and dimethyl disulfide are related to the aroma of seafood. Their ROAV order is HFD > UFD > HPD > HAD, indicating that H. marmoreus using the HFD method have the strongest seafood flavor. The research findings provide theoretical guidance for selecting drying methods and refining the processing of H. marmoreus.

Characterization of Key Odorants in Lushan Yunwu Tea in Response to Intercropping with Flowering Cherry

Lushan Yunwu tea (LSYWT) is a famous green tea in China. However, the effects of intercropping tea with flowering cherry on the overall aroma of tea have not been well understood. In this study, headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) was used for analysis. A total of 54 volatile compounds from eight chemical classes were identified in tea samples from both the intercropping and pure-tea-plantation groups. Principal component analysis (PCA), orthogonal partial least-squares discriminant analysis (OPLS-DA), and odor activity value (OAV) methods combined with sensory evaluation identified cis-jasmone, nonanal, and linalool as the key aroma compounds in the intercropping group. Benzaldehyde, α-farnesene, and methyl benzene were identified as the main volatile compounds in the flowering cherry using headspace solid-phase microextraction/gas chromatography-mass spectrometry (HS-SPME/GC-MS). These findings will enrich the research on tea aroma chemistry and offer new insights into the product development and quality improvement of LSYWT.

The Characterization of the Key Aroma Compounds in Non-Smoked Bacon by Instrumental and Sensory Methods

The aroma profiles in non-smoked bacon were investigated via GC-O-MS, GC × GC-TOFMS, and GC-IMS. GC-O-MS is advantageous for detecting aldehydes. GC × GC-TOFMS is more sensitive to hydrocarbons and alcohols, while GC-IMS detects a balanced range of categories. Only 9 of the 239 detected volatiles were identifiable by all three methods. Therefore, the combination of all three methods proved to be the most effective way to comprehensively analyze the aroma profiles of bacon. Recombination and omission tests were performed using aroma compounds with a flavor dilution (FD) factor greater than 27; five volatiles were identified as key aroma compounds in non-smoked bacon, including hexanal, (E,E)-2,4-decadienal, 1-octen-3-ol, dihydro-5-pentyl-2(3H)-furanone, and 3-methyl-butanoic acid. Among these, hexanal and 1-octen-3-ol exhibited relatively high FD factors and odor activity values (OAVs), so they were confirmed as the primary contributors. Meanwhile, seven volatiles contributed to the unique aroma of non-smoked bacon in different regions. The difference in the aroma of bacon in different regions is mainly due to the content of various volatiles rather than the type. A comprehensive analysis of the aroma in non-smoked bacon can reveal theoretical information for improving the process and quality control of the product.

Solid-phase microextraction coupled to comprehensive multidimensional gas chromatography for food analysis

Solid-phase microextraction and comprehensive multidimensional gas chromatography represent two milestone innovations that occurred in the field of separation science in the 1990s. They have a common root in their introduction and have found a perfect coupling in their evolution and applications. This review will focus on food analysis, where the paradigm has changed significantly over time, moving from a targeted analysis, focusing on a limited number of analytes at the time, to a more holistic approach for assessing quality in a larger sense. Indeed, not only some major markers or contaminants are considered, but a large variety of compounds and their possible interaction, giving rise to the field of foodomics. In order to obtain such detailed information and to answer more sophisticated questions related to food quality and authenticity, the use of SPME-GC × GC-MS has become essential for the comprehensive analysis of volatile and semi-volatile analytes. This article provides a critical review of the various applications of SPME-GC × GC in food analysis, emphasizing the crucial role this coupling plays in this field. Additionally, this review dwells on the importance of appropriate data treatment to fully harness the results obtained to draw accurate and meaningful conclusions.

The flavor substances changes in Fuliang green tea during storage monitoring by GC-MS and GC-IMS

To study the effect of storage (for 0, 3, 6, and 12 months) on the flavor of green tea (GT), we monitored the volatile organic compounds (VOCs) in GT through gas chromatography (GC) combined with ion mobility spectrometry and headspace solid-phase micro extraction, GC-MS (mass spectrometry). Then, relative odor activity value (ROAV) was applied to analyze the aroma contribution of the VOCs. During storage, the polyphenol and caffeine contents gradually decreased from 22.38 % to 18.51 % and from 4.37 % to 3.74 %, respectively, and the total soluble sugar first increased and then decreased (from 4.89 % to 7.16 % and then 5.02 %). Although the total free amino acid contents showed a fluctuating trend, the content of cysteamine increased gradually. The contents of VOCs with positive contribution to GT aroma, including linalool, geraniol, nonanal, and 6-methyl-5-hepten-2-one, decreased. They also contributed less in the ROAV after storage. The ROAVs of nonanal, linalool, and geraniol decreased from 3.37 to 0.79, from 100 to 38.21, and from 2.98 to 1.8, respectively, after 12 months of storage. Principal component analysis can be used to identify the samples with different storage durations based on these data. Given the increase in amount of cysteamine and decrease in that of linalool oxide, oxidation may be not the only factor responsible for tea quality in storage.

Evaluation of perceptual interactions between key aldehydes in Kung Pao Chicken

Aldehydes are the strongest and most abundant aromatic compounds in Kung Pao Chicken. However, the perceptual interactions between these aldehydes are not fully understood. Therefore, the flavor contribution of nine key aldehydes was estimated by determining thresholds. Except for benzaldehyde, the thresholds of all aldehydes measured in tasteless chicken matrices (TM) were significantly larger than their comparable values in water. Based on these results, the perceptual interactions of nine aldehydes were evaluated using S-curves and σ-τ plots. The interactions indicated that 31 of their 36 binary mixtures exhibited additive effects, three had masking effects, while two had synergistic effects. Recombination experiments showed that the addition of aldehydes lowered the odor threshold of aldehyde reconstitution (AR), thereby enhancing the aroma intensity of AR. These findings contribute to a better understanding of Kung Pao Chicken's aroma and can be used to improve its aroma quality.

UV-B application during the aeration process improves the aroma characteristics of oolong tea

Solar withering is essential for the aroma formation of oolong tea, but due to the rainy and humid weather in plantation areas, solar withering became insufficient which seriously limits high-grade oolong tea production. This study aims to investigate ultraviolet B (UV-B) effects on the aroma characteristics of oolong tea and its feasibility in improving tea aroma quality. Sensory evaluation, odorant quantitation, and aroma characteristic analysis suggested UV-B application during the aeration process provided similar effects as solar withering in improving the aroma quality of oolong tea. UV-B application significantly increased fruity and floral odorants (4-hexanolide, α-farnesene, and β-ocimene by 44%, 74%, and 37%, respectively), and decreased green and fatty odorants (hexanal, (E)-2-octenal, and (Z)-4-heptenal by 42%, 45%, and 27%, respectively). These indicate UV-B is crucial for the flowery and fruity aroma formation of oolong tea, which can be potentially applied to oolong tea production, especially under unsunny weather.

Transcriptomic Insights into the Enhanced Aroma of Guangdong Oolong Dry Tea (Camellia sinensis cv. Yashixiang Dancong) in Winter

Winter dry tea (WDT) exhibits a more intense and lasting aroma compared to dry tea from other seasons; however, this conclusion is solely based on sensory outcomes and lacks corroborative theoretical evidence. Our study aimed to analyze the aroma compounds in WDT and investigate the causes behind the formation of WDT's aroma by analyzing the volatile organic compounds (VOCs) in WDT, spring dry tea (SDT), winter fresh leaves (WFLs) and spring fresh leaves (SFLs) by gas chromatography-mass spectrometry (GC-MS), complemented by an analysis of gene expression pertinent to WFLs and SFLs by using transcriptomic analysis. The results revealed a significant increase in total VOCs in WDT compared to SDT, with WDT exhibiting distinct woody aromas as indicated by a higher α-muurolene content. In WFL, the contents of aldehydes and ketones were richer than those in SFL. Notably, the study found that UDP-glycosyltransferase genes in WFLs were significantly up-regulated, potentially promoting the synthesis of terpene glycosides. These terpene glycosides can release terpene aroma compounds during processing, contributing significantly to the intense and lasting aroma of WDT. Overall, this research provides valuable insights into the mechanism behind aroma formation in Guangdong oolong tea harvested during winter.

Exploration of optimal preparation strategy of Chenpi (pericarps of Citrus reticulata Blanco) flavouring essence with great application potential in sugar and salt-reduced foods

To obtain flavouring essence with application potential in sugar and salt-reduced foods, the optimal strategy for extraction and microencapsulation of essential oil (EO) from Chenpi was investigated. UPLC-QTOF-MS/MS and liquid-liquid-extraction-GC-MS confirmed the selectivity for volatiles ranked in hydrodistillation > supercritical fluid extraction > solvent extraction. The aroma characteristic of Chenpi EO was distinguished by 33 key volatiles (screened out via headspace-SPME-GC-MS) and quantitative descriptive analysis. EO extracted by supercritical fluid extraction was preferred for preserving the original aroma of Chenpi and displaying more fruity, honey and floral. Chenpi flavouring essence with superior encapsulation efficiency, particle size, water dispersibility, and thermostability was obtained through optimally microencapsulating EO with gum arabic and maltodextrin (1:1) by high-pressure homogenization coupled with spray drying. Chenpi flavouring essence was able to reduce the usage of sugar and salt by 20 % via enhancing flavour perception of sweetness and saltiness. This study first developed a flavouring essence promisingly effective in both sugar and salt-reduced foods.

Identification of characteristic aroma compounds in chicken meat and their metabolic mechanisms using gas chromatography-olfactometry, odor activity values, and metabolomics

Aroma has an important influence on the aroma quality of chicken meat. This study aimed to identify the characteristic aroma substances in chicken meat and elucidate their metabolic mechanisms. Using gas chromatography-olfactometry and odor activity values, we identified nonanal, octanal, and dimethyl tetrasulfide as the basic characteristic aroma compounds in chicken meat, present in several breeds. Hexanal, 1-octen-3-ol, (E)-2-nonenal, heptanal, and (E,E)-2,4-decadienal were breed-specific aroma compounds found in native Chinese chickens but not in the meat of white-feathered broilers. Metabolomics analysis showed that L-glutamine was an important metabolic marker of nonanal, hexanal, heptanal, octanal, and 1-octen-3-ol. Exogenous supplementation experiments found that L-glutamine increased the content of D-glucosamine-6-P and induced the degradation of L-proline, L-arginine, and L-lysine to enhance the Maillard reaction and promote the formation of nonanal, hexanal, heptanal, octanal, and 1-octen-3-ol, thus improving the aroma profile of chicken meat.

Analysis of aroma components changes in Gannan navel orange at different growth stages by HS-SPME-GC-MS, OAV, and multivariate analysis

The ripe Gannan navel oranges have an appealing aroma, but few studies have reported the changes of these aromatic substances during the growth of navel oranges. In this study, changes of aroma components in Gannan navel orange from 119 to 245 days after flowering were systematically studied using headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) coupled with multivariate analysis, including principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA). A total of 43 and 54 aroma components were identified in pulp and peel of navel orange, respectively. The odor active value (OAV) results indicated that 14 substances were the key aroma components during the growth of navel orange. Among them, the contribution of linalool, β-myrcene and limonene were the highest. The multivariate statistical analysis further confirmed that 14 and 18 compounds could be used as key markers to distinguish the pulp and peel at different growth stages, respectively. Results from this study contributed to a better understanding of the dynamic variation and retention of aroma compounds during navel orange growth, and have great potential for industrial application.

Effect of Leaf Grade on Taste and Aroma of Shaken Hunan Black Tea

Shaken Hunan black tea is an innovative Hunan black tea processed by adding shaking to the traditional Hunan black tea. The quality of shaken black tea is influenced by leaf grades of different maturity. In this study, the taste and aroma quality of shaken Hunan black tea processed with different grades were analyzed by sensory evaluation (SP, HPLC, and HS-SPME/GC-MS). The results showed that shaken Hunan black tea processed with one bud and two leaves has the best quality, which has a sweet, mellow, and slightly floral taste, as well as a floral, honey, and sweet aroma. Moreover, caffeine and EGCG were identified as the most important bitter and astringent substances in shaken Hunan black. Combined with the analysis of GC-MS and OAV analysis, geraniol, jasmone, β-myrcene, citral, and trans-β-ocimene might be the most important components that affect the sweet aroma, while methyl jasmonate, indole, and nerolidol were the key components that affect the floral aroma of shaken Hunan black tea. This study lays a foundation for this study of the taste and aroma characteristics of shaken Hunan black tea and guides enterprises to improve shaken black tea processing technology.

Rapid identification of the geographical origin of Baimudan tea using a Multi-AdaBoost model integrated with Raman Spectroscopy

The potential of Multi-AdaBoost in spectral analysis is substantial, particularly when combined with weak classifiers and trained to develop into a robust classifier. Given the variable quality of Baimudan tea sourced from diverse regions, the novel application of Raman spectroscopy in conjunction with the Multi-AdaBoost model to analyze the geographic origin of Baimudan tea was introduced. Initially, Raman spectra of Baimudan tea from four distinct origins in Fujian province were gathered, namely Fuan (FA), Fuding (FD), Zhenghe (ZH), and Songxi (SX). Decision Tree (DT) and Support Vector Machine (SVM) models were employed as fitting classifiers to construct the Multi-AdaBoost-DT and Multi-AdaBoost-SVM models. The results demonstrated that the Multi-AdaBoost-DT model exhibited significantly improved recognition rates for FA, FD, ZH, and SX origin compared to the DT model, with the average recognition rate increasing from 86.46% to 91.67%. In contrast, the recognition rates for FA and SX origin in the Multi-AdaBoost-SVM model remained unchanged, attributed to the model having reached a local optimum. The recognition rates of FD origin increased from 91.67% to 95.83%, a significant improvement, while those of ZH origin escalated from 83.33% to 87.50%. The average recognition rate increased from 92.71% to 94.79%. Additionally, Multi-AdaBoost-SVM and Multi-AdaBoost-DT enhanced the sensitivity and specificity of the discrimination outcomes. These results corroborated the effectiveness of the proposed Multi-AdaBoost-SVM model in identifying the geographical origin of Baimudan tea. Moreover, the Multi-AdaBoost model demonstrates potential in elevating the discrimination accuracy of weak classifiers, which bodes well for its application in food authentication and quality control.

Effect of shaking manners on floral aroma quality and identification of key floral-aroma-active compounds in Hunan black tea

Shaking is a key process effecting the floral aroma of Hunan black tea (HBT). In this study, the aroma composition of HBTs shaken in the early withering stage (ES1, ES1 + LS1, and ES2), shaken in the late withering stage (LS1), and not shaken (NS), and the identification of main floral aroma compounds were analyzed using sensory evaluation combined with gas chromatography-mass spectrometry (GC-MS), gas chromatography-olfactometry (GC-O), and aroma recombination experiments. Sensory evaluation results showed that the floral aroma of HBT shaken in the early withering stage was with high intensity, whereas HBT shaken in the late withering stage had low-intensity floral aroma. GC-MS identified a total number of 81 differential volatile compounds in HBT, including 30 esters, 18 aldehydes, 15 alcohols, 12 terpenes, 4 ketones, and 2 nitrogen-containing compounds. Further screening of important floral aroma differential compounds was performed using sensory-guided, odor activity value (OAV), and GC-O analysis, which identified three critical floral aroma differential compounds. Eventually, absolute quantification analysis and aroma recombination experiments confirmed that indole and methyl jasmonate were the most critical compounds of HBT determining floral aroma intensity. The findings of this study provide valuable guidance for the production of HBT with rich floral aroma attributes.

Comparative Metabolomic Analysis Reveals the Differences in Nonvolatile and Volatile Metabolites and Their Quality Characteristics in Beauty Tea with Different Extents of Punctured Leaves by Tea Green Leafhopper

The fresh leaves were processed into beauty tea from the Camellia sinensis "Jinxuan" cultivar, which were punctured by tea green leafhoppers to different extents. Low-puncturing dry tea (LPDT) exhibited a superior quality. Altogether, 101 and 129 differential metabolites, including tea polyphenols, lipids, and saccharides, were identified from the fresh leaves and dry beauty tea, respectively. Most metabolite levels increased in the fresh leaves punctured by leafhoppers, but the opposite was observed for the dry beauty tea. According to relative odor activity values (rOAVs) and partial least-squares discriminant analysis (PLS-DA), four characteristic volatiles, including linalool, geraniol, benzeneacetaldehyde, and dihydrolinalool, were selected. Mechanical injury to leaves caused by leafhoppers, watery saliva secreted by the leafhopper, and different water contents of the fresh leaves in different puncturing degrees are the possible reasons for the difference in the quality of the beauty tea with different levels of puncturing. Overall, this study identified a wide range of chemicals that are affected by the degrees of leafhopper puncturing.

Identification of key volatile and odor-active compounds in 10 main fragrance types of Fenghuang Dancong tea using HS-SPME/GC-MS combined with multivariate analysis

Fenghuang Dancong tea (FHDC), a famous oolong tea originating from Guangdong Province in China, is known for its rich and unique fragrance. Nevertheless, the identification of the key aroma compounds with the difference fragrance types of FHDC remains uncertain. In order to characteristic the volatile components in different fragrance types of FHDC, 10 well-known fragrance types of FHDC and Tieguanyin (TGY) as a control were analyzed by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography mass spectrometry (GC-MS). Results indicated that 172 volatile compounds were identified as common volatile compounds among all the tea samples. A total of 16 compounds were identified as key compounds that could be used to distinguish between FHDC and TGY. Among the 10 FHDC fragrance types, indole, hotrienol, benzyl nitrile, and jasmine lactone were found to be the most abundant compounds. Despite the presence of certain similarities in aroma components, each type exhibits unique fragrance characteristics as a result of variation in compound composition content and proportion. Furthermore, using statistical and odor activity value analysis, 20 aroma-active compounds were recognized as potential characteristic markers accountable for the diverse fragrance types of FHDC. This research enhances our comprehension of the various fragrance types of FHDC and provides reference values for their rapid identification in the market.

Effects of different over-fired drying methods on the aroma of Lu'an Guapian tea

Over-fired drying, a crucial process in the production of Lu'an Guapian (LAGP) tea, greatly enriches the tea's aroma. In this study, the aroma compounds of LAGP tea processed through pulley charcoal drying (PCD), roller drying (RD), roller-conveyor drying (RCD), and hot air drying (HD) were analyzed using gas chromatography-mass spectrometry. A subsequent analysis of aroma extraction dilution analysis and odor activity values revealed that (E)-β-ionone, dimethyl sulfide, (E,E)-2,4-heptadienal, geraniol, linalool, benzeneacetaldehyde, coumarin, 2-ethyl-3,5-dimethyl-pyrazine, indole, hexanal, (Z)-jasmone, and (Z)-3-hexen-1-ol were the key contributors to the samples' aroma variation. Moreover, a quantitative descriptive analysis and aroma recombination and omission experiments analysis revealed that (E)-β-ionone is the most critical contributor to the formation of floral aroma in tea processed using PCD, whereas (E,E)-2,4-heptadienal is responsible for the more pronounced fresh aroma in tea processed using HD. In addition, 2-ethyl-3,5-dimethyl-pyrazine contributes to the formation of a roasted aroma in tea processed using RD and RCD. The study results provide a theoretical basis for choosing the processing method, especially for drying, to obtain high-quality LAGP tea.

Characterization of key volatile compounds in jasmine tea infusion with different amount of flowers

The quality of jasmine tea is related to the volatiles of its infusion. In this study, the volatiles of jasmine tea infusion were extracted under the optimal conditions with a 50/30 μm DVB/CAR/PDMS fiber, tea/water ratio of 1:25 and extraction time of 5 min. A total of 204 volatiles were analyzed by comprehensive two-dimensional gas chromatography-quadrupole time-of-flight mass spectrometry (GC × GC-Q-TOF-MS). Twenty-five compounds were identified as the key volatile compounds by fold change (FC), orthogonal partial least squares discriminant analysis (OPLS-DA), and two-way orthogonal partial least squares analysis (O2PLS). Then optimal amount of flowers (80%-120%) was obtained by the equation describing key volatiles and quality of jasmine tea infusion. And 80% amount of flowers was more appropriate considering the production cost and more pleasant taste. This study laid a foundation for the extraction and research of volatiles of tea infusion and guided the reasonable amount of flowers to produce jasmine tea.

Microwaves affect the formation of volatile compounds in peper powder by changing the nucleophilic addition reactions in Maillard reactions

We explored the effect of microwave heating (MWH) and electric heating (ETH) on the volatile compounds (VCs) of pepper (Capsicum annuum L.). The spectral of the produced melanoidins by baking were used to screen samples with similar baking degrees. Mass spectrometry was used to detect the differences of VCs in samples. The results showed a dose-dependent effect between the intensity of absorption and fluorescence of melanoidins, which can be utilized as indicators for assessment baking degree. MWH samples produced larger variety of VCs than ETH. Changes in the variety and content of VCs infer changes in the flavor of pepper. According to the mechanism of Maillard reaction (MR) and MWH, it was deduced that MWH changes the type of chemical reaction in MR by affecting the distribution of valence electrons in the compounds. Therefore, MWH can be used as a novel method to modify the VCs and flavor of peppers.

Decoding the Chemical Signatures and Sensory Profiles of Enshi Yulu: Insights from Diverse Tea Cultivars

Enshi Yulu, a renowned Chinese steamed green tea, is highly valued for its unique sensory attributes. To enhance our comprehensive understanding of the metabolic variation induced by steaming fixation, we investigated the overall chemical profiles and organoleptic quality of Enshi Yulu from different tea cultivars (Longjing 43, Xiapu Chunbolv, and Zhongcha 108). The relationships between sensory traits and non-volatiles/volatiles were evaluated. A total of 58 volatiles and 18 non-volatiles were identified as characteristic compounds for discriminating among the three tea cultivars, and the majority were correlated with sensory attributes. The "mellow" taste was associated with L-aspartic acid, L-asparagine, L-tyrosine, L-valine, EGC, EC, and ECG, while gallic acid and theobromine contributed to the "astringent" taste. "Kokumi" contributors were identified as L-methionine, L-lysine, and GCG. Enshi Yulu displayed a "pure" and "clean and refreshing" aroma associated with similar volatiles like benzyl alcohol, δ-cadinene, and muurolol. The composition of volatile compounds related to the "chestnut" flavor was complex, including aromatic heterocycles, acids, ketones, terpenes, and terpene derivatives. The key contributors to the "fresh" flavor were identified as linalool oxides. This study provides valuable insights into the sensory-related chemical profiles of Enshi Yulu, offering essential information for flavor and quality identification of Enshi Yulu.

Analysis of Volatile Profile and Aromatic Characteristics of Raw Pu-erh Tea during Storage Based on GC-MS and Odor Activity Value

Volatile constituents are critical to the flavor of tea, but their changes in raw Pu-erh tea (RAPT) during storage have not been clearly understood. This work aimed to investigate the volatile composition and their changes at various storage durations. The volatile profile of RAPT was determined using headspace solid-phase microextraction in combination gas chromatography-mass spectrometry. A total of 130 volatile compounds were identified in RAPT samples, and 64 of them were shared by all samples. The aroma attributes of RAPT over a storage period ranging from 0 to 10 years were assessed through the combination of odor activity value (OAV), aroma characteristic influence(ACI) value, and multivariate statistical analysis. The results revealed that RAPT exhibited a distinct floral and fruity aroma profile after storage for approximately 3-4 years. A notable shift in aroma was observed after 3-4 years of storage, indicating a significant turning point. Furthermore, the likely notable shift after 10 years of storage may signify the second turning point. According to the odor activity value (OAV ≥ 100), eight key volatile compounds were identified: linalool, α-terpineol, geraniol, trans-β-ionone, α-ionone, (E,E)-2,4-heptadienal, 1-octanol, and octanal. Combining OAV (≥100) and ACI (≥1), five compounds, namely linalool, (E,E)-2,4-heptadienal, (Z)-3-hexen-1-ol, 2,6,10,10-tetramethyl-1-oxaspiro [4.5]dec-6-ene, and octanal, were identified as significant contributors to the aroma. The results offer a scientific foundation and valuable insights for understanding the volatile composition of RAPT and their changes during storage.

Characterization of the Sensory Properties and Quality Components of Huangjin Green Tea Based on Molecular Sensory-Omics

Huangjin green tea (HJC) is one of the most famous regional green teas in China, and has gained attention for its unique flavor. Research on HJC has focused mainly on the synthesis of L-theanine, with fewer studies concentrating on sensory characteristics. In this study, molecular sensory science techniques, including color analysis, gas chromatography-ion mobility spectrometry, and E-tongue, were used to characterize the sensory properties of HJC, with Fuding Dabai and Anji Baicha teas used as conventional and high amino acid controls, respectively. The sensory characteristics and main quality components of HJC lie somewhere between these two other teas, and somewhat closer to the conventional control. They were difficult to distinguish by color, but significant differences exist in terms of volatile organic compounds (VOCs), E-tongue values on bitterness and astringency, and their contents of major taste components. VOCs such as (E)-2-octenal, linalool, ethyl acrylate, ethyl acetate, and 2-methyl-3-furanethiol were found to be the main differential components that contributed to aroma, significantly influencing the tender chestnut aroma of HJC. Free amino acids, tea polyphenols, and ester catechins were the main differential components responsible for taste, and its harmonious phenol-to-ammonia ratio was found to affect the fresh, mellow, heavy, and brisk taste of HJC.

Characterization of the Key Aroma Compounds in Dong Ding Oolong Tea by Application of the Sensomics Approach

The Dong Ding oolong tea (DDT), grown and produced in Taiwan, is widely appreciated for its unique flavor. Despite its popularity, research on the aroma components of DDT remains incomplete. To address this gap, this study employed a sensomics approach to comprehensively characterize the key aroma compounds in DDT. Firstly, sensory evaluation showed that DDT had a prominent caramel aroma. Subsequent analysis using gas chromatography-olfactory mass spectrometry (GC-O-MS) and comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOF-MS) identified a total of 23 aroma-active compounds in DDT. Notably, three pyrazine compounds with roasted notes, namely 2-ethyl-5-methylpyrazine, 2-ethyl-3,5-dimethylpyrazine, and 2,3-diethyl-5-methylpyrazine, along with seven floral- and fruit-smelling compounds, namely 6-methyl-5-hepten-2-one, 3,5-octadien-2-one, linalool, (E)-linalool oxide, geraniol, (Z)-jasmone, and (E)-nerolidol, were identified as the key aroma compounds of DDT. Omission experiments further validated the significant contribution of the three pyrazines to the caramel aroma of DDT. Moreover, the content of 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, (Z)-jasmone, 6-methyl-5-hepten-2-one and 2-ethyl-5-methylpyrazine was found to be higher in the high-grade samples, while (E)-nerolidol, linalool, geraniol and 3,5-octadien-2-one were found to be more abundant in the medium-grade samples. These findings provide valuable information for a better understanding of the flavor attributes of DDT.

Unraveling the contribution of aroma-active and chiral compounds to different grade of Yashi Xiang teas using stir bar sorptive extraction

Yashi Xiang (YSX) is a flavor of Fenghuang Dancong tea and famous for its name and floral aroma, which is a type of semi-fermented oolong tea. However, previous research into the aroma characteristics of YSX tea mostly focused on the aroma compounds, and little research on chiral compounds in YSX has been performed. Therefore, the current study was conducted to explore the aroma characteristics of YSX tea from the perspective of enantiomers of chiral compounds. A total of 12 enantiomers were determined in this study, among them, (R)-(-)-α-ionone, (S)-(+)-linalool, (1S,2S)-(+)-methyl jasmonate, (S)-z-nerolidol, (R)-(+)-limonene, and (S)-(-)-limonene have important effects on the aroma components of YSX tea. The ER ratios of the enantiomers were different in samples of different grades. Therefore, this parameter can be used to identify the grade and authenticity of YSX tea. PRACTICAL APPLICATION: The study illuminates the aroma characteristics of YSX tea from the perspective of enantiomers of chiral compounds, which have important effects on the aroma components of YSX tea. It established an ER ratio system to effectively distinguish the grade and authenticity of YSX tea by comparing the ER of YSX tea. Focusing on analyzing the chiral compounds in the aroma of YSX tea is helpful in providing a theoretical basis for the authenticity of the precious tea and improving of the quality of YSX tea products.

Revelation of volatile contributions in green teas with different aroma types by GC-MS and GC-IMS

Aroma types of green teas associate with their commercial prices and consumer acceptance, mainly including floral-like (HX), chestnut-like (LX), and fresh (QX) aromas. However, the volatile differences and specificities in these aroma types are still unclear. Herein, Taiping Houkui green teas with HX, LX, and QX aromas were processed separately with the same fresh tea leaves. Ninety-four and seventy-eight volatiles were detected and identified by headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) and headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS), respectively. Candidate differential volatiles among the tea samples were determined by the variable importance in projection (VIP) of the partial least squares-discriminant analysis (PLS-DA) and were further confirmed by the relative odor activity value (ROAV) and odor description. The volatiles 1-hexanol, linalool oxide (furanoid), linalool, geraniol, (E)-β-ionone, isoamyl acetate, and 2-methylpropanal enriched in HX and contributed to the floral-like aroma, while 3-methylbutanal, 2-ethyl-1-hexanol, indole, β-damascone, and cedrol enriched in LX and contributed to the chestnut-like aroma. This study reveals the specificities and contributions of volatiles in green teas with different aromas, thus providing new insights into the molecular basis of different flavored teas, benefiting for their precision processing and targeted quality control.

Metabolite analysis and sensory evaluation reveal the effect of roasting on the characteristic flavor of large-leaf yellow tea

Roasting is essential for processing large-leaf yellow tea (LYT). However, the effect of the roasting on the metabolic and sensory profiles of LYT remains unknown. Herein, the metabolomics and sensory quality of LYT at five roasting degrees were evaluated by liquid/gas chromatography mass spectrometry and quantitative descriptive analysis. A higher degree of roasting resulted in a significantly stronger crispy rice, fried rice, and smoky-burnt aroma (p < 0.05), which is closely associated with heterocyclic compound accumulation (concentrations: 6.47 ± 0.27 - 1065.00 ± 5.58 µg/g). Amino acids, catechins, flavonoid glycosides and N-ethyl-2-pyrrolidone-substituted flavan-3-ol varied with roasting degree. The enhancement of crispy-rice and burnt flavor coupled with the reduction of bitterness and astringency. Correlations analysis revealed the essential compounds responsible for roasting degree, including 2,3-diethyl-5-methylpyrazine, hexanal, isoleucine, N-ethyl-2-pyrrolidone-substituted flavan-3-ol (EPSF), and others. These findings provide a theoretical basis for improving the specific flavors of LYT.

Effects of Sun Withering Degree on Black Tea Quality Revealed via Non-Targeted Metabolomics

In this study, the effects of different sun withering degrees (75% (CK), 69% (S69), 66% (S66), 63% (S63), and 60% (S60) water content in the withered leaves) on black tea sensory quality were investigated by means of sensory evaluation plus metabolomics analysis. Sensory evaluation results showed higher sensory quality scores for the black tea in S69-S66, due to better freshness, sweeter taste, and a sweet and even floral and fruity aroma. Additionally, 65 non-volatile components were identified using Ultra Performance Liquid Chromatography-Quadrupole-Time of Flight-Mass Spectrometry (UPLC-Q-TOF/MS). Among them, the content increase of amino acids and theaflavins was found to promote the freshness and sweetness of black tea. The aroma of tea was analyzed using combined Solvent Assisted Flavor Evaporation-Gas Chromatography-Mass Spectrometry (SAFE-GC-MS) and Headspace-Solid Phase Micro Extract-Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS), and 180 volatiles were identified, including 38 variable importance in projection (VIP) > 1 (p < 0.05) and 25 Odor Activity Value (OAV) > 1 volatiles. Statistical analysis revealed 11 volatiles as potential major aroma differential metabolites in black tea with a different sun withering degree, such as volatile terpenoids (linalool, geraniol, (E)-citral, and β-myrcene), amino-acid-derived volatiles (benzeneethanol, benzeneacetaldehyde, and methyl salicylate), carotenoid-derived volatiles (jasmone and β-damascenone), and fatty-acid-derived volatiles ((Z)-3-hexen-1-ol and (E)-2-hexenal). Among them, volatile terpenoids and amino acid derived volatiles mainly contributed to the floral and fruity aroma quality of sun-withered black tea.

Characterization of the key odorants in floral aroma green tea based on GC-E-Nose, GC-IMS, GC-MS and aroma recombination and investigation of the dynamic changes and aroma formation during processing

To characterize the key odorants of floral aroma green tea (FAGT) and reveal its dynamic evolution during processing, the volatile metabolites in FAGT during the whole processing were analyzed by integrated volatolomics techniques, relative odor activity value (rOAV), aroma recombination, and multivariate statistical analysis. The volatile profiles undergone significant changes during processing, especially in the withering and fixation stages. A total of 184 volatile compounds were identified (∼53.26% by GC-MS). Among them, 7 volatiles with rOAV > 1 were identified as characteristic odorants of FAGT, and most of these compounds reached the highest in withering stage. According to the formation pathways, these key odorants could be divided into four categories: fatty acid-derived volatiles, glycoside-derived volatiles, amino acid-derived volatiles, and carotenoid-derived volatiles. Our study provides a comprehensive strategy to elucidate changes in volatile profiles during processing and lays a theoretical foundation for the targeted processing of high-quality green tea.

Flavor perception and health benefits of tea

As one of the most consumed non-alcoholic beverages in the world, tea is acclaimed for its pleasant flavor and various health benefits. Different types of tea present a distinctive flavor and bioactivity due to the changes in the composition and proportion of respective compounds. This article aimed to provide a more comprehensive understanding of tea flavor (including aroma and taste) and the character of tea in preventing and alleviating diseases. The recent advanced modern analytical techniques for revealing flavor components in tea, including enrichment, identification, quantitation, statistics, and sensory evaluation methodologies, were summarized in the following content. Besides, the role of tea in anti-cancer, preventing cardiovascular disease and metabolic syndrome, anti-aging and neuroprotection, and regulating gut microbiota was also listed in this article. Moreover, questions and outlooks were mentioned to objectify tea products' flavor quality and health benefits on a molecular level and significantly promote our understanding of the comprehensive value of tea as a satisfactory health beverage in the future.

Formation of aroma characteristics driven by volatile components during long-term storage of An tea

The aim of this study was to reveal the molecular basis of aroma changes during storage of An tea (AT). The key volatile compounds in AT were screened using SPME-GC-MS and SPE-GC-MS analytical techniques in combination with odor activity value (OAV) and flavor dilution factor (FD). The results showed that with the increase of storage time the stale and woody aromas were revealed. Esters, acids and hydrocarbons are the main types of volatile compounds in AT, and their content accounts for 52.69 %-61.29 % of the total volatile compounds. The key volatile compounds with stale and woody aromas during AT storage were obtained by OAV value and FD value, namely ketoisophorone (flavor dilution factor, FD = 64), linalool oxide C (FD = 64), 1-octen-3-ol (OAV > 1, FD = 32), 1,2-dimethoxybenzene (FD = 16), naphthalene (OAV > 1, FD = 32), 3,4-dimethoxytoluene (FD = 16), and 1,2,3-trimethoxybenzene (FD = 8). Our research provides a scientific basis and insights for the improvement of quality during the storage of dark tea.

Contribution of traditional deep fermentation to volatile metabolites and odor characteristics of Wuyi rock tea

Fermentation is extremely important for the formation of the special flavor of Wuyi rock tea. This study determined volatile metabolite contents using GC-MS technique and futher analyzed their odor characteristics during the traditional deep fermentation technology of Wuyi rock tea. The results showed that 17 characteristic compounds significantly changed during the first stage of the preliminary processing, namely fresh leaves, withering and fermentation. The key to the formation of floral aroma lied in dihydromyrcenol, and the woody aroma derived from six terpenoids, and their synthesis depended on dihydromyrcenol content. The fruity aroma was dominated by six esters, and the fruity aroma mainly came from (Z) -3-hexen-1-yl butyrate, (E) -3-hexen-1-yl butyrate and 5-Hexenyl butyrate. This study provided an important theoretical and practical basis for improving the preliminary processing of Wuyi rock tea.