Changes of volatile compounds and odor profiles in Wuyi rock tea during processing

Understanding the dynamic changes of volatile and non-volatile metabolites in black tea during processing by integrated volatolomics and UHPLC-HRMS analysis

Processing technology has an important effect on the flavor quality of black tea. However, the dynamic changes of volatile and non-volatile metabolites in black tea during processing are poorly understood. In this study, the volatile and non-volatile compounds during black tea processing were comprehensively characterized by integrated volatolomics and UHPLC-Q-Exactive/MS analysis. Volatile and non-volatile metabolites changed continuously throughout the processing process, especially during the withering stage. A total of 178 volatile metabolites and 103 non-volatile metabolites were identified. Among them, 11 volatile components with relative odor activity value greater than 1 (including dimethyl sulfide, 3-methylbutanal, 2-methylbutanal, β-myrcene, β-ocimene, linalool, methyl salicylate, β-cyclocitral, β-citral, citral, and β-ionone) were regarded as key aroma-active components responsible for finished black tea with sweet aroma. This study provides a comprehensive understanding of dynamic evolution trajectory of volatile and non-volatile metabolites during processing, which lays a theoretical foundation for the targeted processing of high-quality black tea.

From heat to flavor: Unlocking new chemical signatures to discriminate Wuyi rock tea under light and moderate roasting

Roasting is crucial for the distinct flavor of Wuyi rock tea (WRT). This study applied untargeted metabolomics to investigate the effects of roasting on 139 WRT samples roasted at light fire (LF) or moderate fire (MF) intensities. Compared to LF, MF roasting led to a decrease in the cis/trans flavanol ratio by 56% and theanine by 85%, while increasing the levels of N-ethyl-2-pyrrolidione-substituted flavanols (EPSFs), flavonol aglycones and flavone C-glycosides. Two new roast markers, 3-p-coumaroyl 1,5-lactone and 4-p-coumaroyl 1,5-lactone, were identified in WRT and their formation increased with roasting temperature. MF roasting facilitated the formation of diverse heterocycles (e.g., pyrazines) and aldehydes (e.g., (Z)-4-heptenal and (E,E)-2.4-decadienal) that contributed to the augmented roasted and fatty odors in WRT. Additionally, the Maillard product furfuryl methyl ether was solely detected in MF samples. These findings provide novel insights into roast markers in WRT with implications for improving quality control measures during tea roasting.

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.

Aromatic profiles and enantiomeric distributions of volatile compounds during the ripening of Dendropanax dentiger honey

Dendropanax dentiger honey (DDH) is a specialty herbal honey from China. Previous research on DDH has mostly focused on its composition and potential chemical markers, no studies have been conducted on the changes in aroma characteristics and chiral odorants during its maturation. Therefore, the present study aims to address the missing parts. The proportions and total concentrations of 185 volatile compounds identified in different classes varied with DDHs ripening. Fourteen common odor-active compounds were identified by odor activity values (OAVs) and GC-olfactometry (GC-O) analysis. The aroma profiles of DDHs were observed to vary at different ripening stages, although the dominant aroma characteristic was "fruity" aroma, which became more pronounced with increasing maturity. The enantiomeric contents and distributions of 7 volatile enantiomers were related to specific physicochemical indicators and the maturity of DDHs, among which the enantiomers of linalool oxide A may be a potential indicator to identify its maturity. Furthermore, precise quantification and OAVs calculation showed that the enantiomer (2S, 5S)-linalool oxide A presented the highest concentration (8.83-27.39 ng/mL) and only the enantiomer R-linalool (OAVs: 5.56-6.14) was an important contributor to the aroma profiles of DDHs at different stages of maturity. These results provided a new research idea for quality control and identification of DDHs at different maturity stages.

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 shaking on the improvement of aroma quality and transformation of volatile metabolites in black tea

Shaking is an innovative technology employed in black tea processing to enhance flavor. However, the effects of shaking on the evolutionary mechanisms of volatile metabolites (VMs) remain unclear. In this study, we compared the effects of a shaking-withering method with those of traditional withering on the flavor and VMs transformation of black tea. The results showed that black tea treated with shaking exhibited excellent quality with floral and fruity aroma. Based on gas chromatography-tandem mass spectrometry, 128 VMs (eight categories) were detected. Combining variable importance projection with odor activity value analysis, eight key differential VMs were identified. Shaking could promote the oxidative degradation of fatty acids and carotenoids and modulate the biosynthesis of terpenoids to facilitate the formation of floral/fruity VMs (such as (Z)-hexanoic acid-3-hexenyl ester, ethyl hexanoate, trans-β-ionone, and decanal). Our findings provide theoretical guidance for the production of high-quality black tea with floral and fruity aromas.

Widely targeted metabolomics analysis reveals the formation of nonvolatile flavor qualities during oolong tea manufacturing: a case study of Jinguanyin

Background

The manufacturing processes of oolong tea significantly impact its nonvolatile components, leading to the emergence of distinct flavor attributes. Understanding the dynamic changes in nonvolatile components during the manufacturing stages of the Jinguanyin (JGY) cultivar is crucial for unraveling the potential mechanism behind flavor formation.

Methods

Comprehensive metabolomics and sensomics analyses were conducted to investigate the dynamic changes in nonvolatile components throughout various phases of oolong tea processing, focusing on the JGY cultivar.

Results

A total of 1,005 nonvolatile metabolites were detected, with 562 recognized as significant differential metabolites during various phases of oolong tea processing. Notably, the third turning-over, third setting, and high-temperature treatments exhibited the most significant effects on the nonvolatile metabolites of oolong tea. JGY finished tea demonstrated a characteristic flavor profile, marked by mellowness, sweetness in aftertaste, and a significant Yin rhyme. This flavor profile was collectively promoted by the accumulation of amino acids and organic acids, the decrease in flavonols (3-O-glycosides) and sugar substances, the alteration of phenolic acids, and the stabilization of caffeine.

Conclusion

This study contribute to the understanding of the formation of oolong tea flavor qualities. The dynamic changes observed in various types of nonvolatile compounds during oolong tea processing shed light on the intricate interplay of metabolites and their influence on the final flavor characteristics.

Analysis of Characteristics in the Macro-Composition and Volatile Compounds of Understory Xiaobai White Tea

Understory planting affects the growth environment of tea plants, regulating the tea plant growth and the formation of secondary metabolites, which in turn affects the flavor of Xiaobai white tea. The present research adopted biochemical composition determination, widely targeted volatilities (WTV) analysis, multivariate statistical analysis, and odor activity value (OAV) analysis to analyze the characteristics in the macro-composition and volatile compounds of understory white tea. The sensory evaluation results indicated that understory Xiaobai white tea (LWTs) was stronger than ordinary Xiaobai white tea (PWTs) in terms of the taste of smoothness, sweetness, and thickness as well as the aromas of the flower and sweet. Understory planting reduced light intensity and air temperature, increased air humidity, organic matter, total nitrogen, and available nitrogen contents, which improved the growth environment of tea plants. The phytochemical analysis showed that the water-extractable substances, caffeine, flavonoids, and soluble sugar contents of understory tea fresh-leaf (LF) were higher than those of ordinary fresh-leaf (PF). The phytochemical analysis showed that the free amino acids, theaflavins, thearubigins, water-extractable substances, and tea polyphenols contents of LWTs were significantly higher than those of PWTs, which may explain the higher smoothness, sweetness, and thickness scores of LWTs than those of PWTs. The 2-heptanol, 2-decane, damasone, and cedar alcohol contents were significantly higher in LWTs than in PWTs, which may result in stronger flowery and sweet aromas in LWTs than in PWTs. These results provide a firm experimental basis for the observed differences in the flavor of LWTs and PWTs.

Comprehensive applications of metabolomics on tea science and technology: Opportunities, hurdles, and perspectives

With the development of metabolomics analytical techniques, relevant studies have increased in recent decades. The procedures of metabolomics analysis mainly include sample preparation, data acquisition and pre-processing, multivariate statistical analysis, as well as maker compounds' identification. In the present review, we summarized the published articles of tea metabolomics regarding different analytical tools, such as mass spectrometry, nuclear magnetic resonance, ultraviolet-visible spectrometry, and Fourier transform infrared spectrometry. The metabolite variation of fresh tea leaves with different treatments, such as biotic/abiotic stress, horticultural measures, and nutritional supplies was reviewed. Furthermore, the changes of chemical composition of processed tea samples under different processing technologies were also profiled. Since the identification of critical or marker metabolites is a complicated task, we also discussed the procedure of metabolite identification to clarify the importance of omics data analysis. The present review provides a workflow diagram for tea metabolomics research and also the perspectives of related studies in the future.

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)-β-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 β-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.

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.

Non-targeted metabolomics characterization of flavor formation of Lichuan black tea processed from different cultivars in Enshi

Nine tea cultivars planted in Enshi were selected and processed into "Lichuan black tea". Sensory evaluation showed that cultivar had the greatest influence on taste and aroma quality, including sweetness, umami and concentration of taste, as well as sweet and floral fragrances of aroma. The non-volatile and volatile components were identified by UPLC-Q-TOF/MS and GC-MS, and PCA analysis showed good separation between cultivars, which could cause the difference in quality. Baiyaqilan, Meizhan and Echa 10 had a floral aroma, with obvious difference in their aromatic composition from other cultivars. Moreover, Echa 10 also had a strong sweet aroma. The key aroma components in Echa 10 (with the largest cultivation area) were further investigated by GC-O-MS combined with odor activity value (OAV) analysis, included β-damascenone, phenylethylaldehyde, nonenal, geraniol, linalool, jasmonone, (E)-2-nonenal, β-cyclocitral, (E)-β-ocimene, methyl salicylate, β-ionone, 2,6,10,10-tetramethyl-1-oxaspiro[4.5]dec-6-ene, citral, β-myrcene, nerol, phenethyl alcohol, benzaldehyde, hexanal, nonanoic acid, and jasmin lactone.

Widely targeted metabolomics reveals the effect of different raw materials and drying methods on the quality of instant tea

Introduction

Instant teas are particularly rich in tea polyphenols and caffeine and have great potential as food ingredients or additives to improve the quality of food and enhance their nutritional and commercial value.

Methods

To determine the relationships between raw material, drying method, and sensory and other quality attributes, instant teas were prepared from three tea varieties, namely black, green and jasmine tea, using two drying methods, namely spray-drying (SD) and freeze-drying (FD).

Results

Both the raw tea material and drying method influenced the quality of the finished instant teas. Black tea was quality stable under two drying, while green tea taste deteriorated much after SD. Jasmine tea must be produced from FD due to huge aroma deterioration after SD. FD produced instant tea with higher sensory quality, which was attributed to the lower processing temperature. Chemical compositional analysis and widely targeted metabolomics revealed that SD caused greater degradation of tea biochemical components. The flavonoids content changed markedly after drying, and metabolomics, combined with OPLS-DA, was able to differentiate the three varieties of tea. Instant tea preparations via SD often lost a large proportion of the original tea aroma compounds, but FD minimized the loss of floral and fruity aroma compounds. Changes in the tea flavonoids composition, especially during drying, contributed to the flavor development of instant tea.

Discussion

These results will provide an practicle method for high-quality instant tea production through choosing proper raw tea material and lowering down drying temperature with non-thermal technologies like FD.

Characterizing and Decoding the Effects of Different Fermentation Levels on Key Aroma Substances of Congou Black Tea by Sensomics

Fermentation is the key technology for black tea aroma formation. The key aroma substances of black tea at different fermentation stages (unfermented (WDY), underfermented (F1H), fully fermented (F4H), and overfermented (F8H)) were characterized by the methodology of Sensomics. Aroma extract dilution analysis was performed on volatile fractions extracted by using solvent-assisted flavor evaporation and solid-phase microextraction, yielding 93 odor-active areas. Internal standard method plus stable isotope dilution analysis was used for quantitative analysis. The omission experiment identified 23 aroma substances. Further reduction and addition experiments revealed phenylacetaldehyde, (E,E)-2,4-heptadienal, geraniol, linalool, β-damascenone, 2-methylbutyraldehyde, dimethyl sulfide, and isovaleraldehyde with odor activity values (OAV) > 100 as the characteristic aroma components of F4H and also as the main contributors to aroma differences between different fermentation degrees. The green odor of (E,E)-2,4-heptadienal was highlighted in WDY and F1H relative to that in F4H due to the lower contribution of phenylacetaldehyde and β-damascenone in the former two samples. Additionally, excessive OAV increase of fatty aldehydes in F8H masked its similar floral and fruity aroma.

The Impact of Different Cooking Methods on the Flavor Profile of Fermented Chinese Spicy Cabbage

Chinese spicy cabbage (CSC) is a common traditional fermented vegetable mainly made of Chinese cabbage. In addition to eating raw, boiling and stir-frying are the most common cooking methods for CSC. To identify the impacts of boiling or stir-frying on the quality of CSC, the physicochemical properties, flavor compounds, and sensory properties of CSC were analyzed. A total of 47 volatile flavor compounds (VFCs) were detected by gas chromatography-mass spectrometry. Sulfide was determined as the main flavor compound of CSC, mainly contributed by cabbage, garlic, and onion odors. The content of sulfide decreased significantly after cooking. Nonanal, geranyl acetate, and linalool were newly generated after boiling with odor activity value (OAV) > 1, and contributed fatty, sweet, fruity, and floral odors to BL-CSC. 1-Octen-3-one, 1-octen-3-ol, octanal, nonanal, and (E)-2-nonenal were newly generated after stir-frying with OAV > 1, and contributed mushroom, fatty, and green odors to SF-CSC. Diallyl trisulfide, nonanal, (E)-β-ionone, β-sesquiphellandrene, and (E)-2-decenal were considered as the potential key aroma compounds (KACs) to distinguish the CSCs after different heat treatment. After cooking, the total titratable acidity of CSC increased and the sensory properties changed significantly. This study provides valuable information and guidance on the sensory and flavor changes of thermal processing fermented vegetables.

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.

Chemical Analysis of Various Tea Samples Concerning Volatile Compounds, Fatty Acids, Minerals and Assessment of Their Thermal Behavior

Tea is the most consumed drink worldwide due to its pleasant taste and various beneficial effects on human health. This paper assesses the physicochemical analysis of different varieties of tea (leaves, flowers, and instant) after prior drying and fine grinding. The thermal decomposition behavior of the tea components shows that the tea has three stages of decomposition, depending on temperature. The first stage was attributed to the volatilization of water, while the second stage involved the degradation of volatiles, polyphenols, and fatty acids. The degradation of cellulose, hemicellulose, and lignin content occurs at the highest temperature of 400 °C in the third stage. A total of 66 volatile compounds, divided into eight classes, were identified in the tea samples. The volatile compounds were classified into nine odor classes: floral, fruity, green, sweet, chemical, woody, citrus, roasted, and alcohol. In all flower and leaf tea samples, monounsaturated (MUFAs), polyunsaturated (PUFAs), and saturated fatty acids (SFAs) were identified. A high content of omega-6 was quantified in acacia, Saint John's Wort, rose, and yarrow, while omega-3 was found in mint, Saint John's Wort, green, blueberry, and lavender samples. The flower and leaf tea samples studied could be a good dietary source of polyphenolic compounds, essential elements. In instant tea samples, a low quantity of polyphenols and major elements were identified. The physicochemical analysis demonstrated that both flower and leaf teas have high-quality properties when compared to instant tea.

Identification of Volatile Markers during Early Zygosaccharomyces rouxii Contamination in Mature and Immature Jujube Honey

Osmotolerant yeasts are considered one of the major contaminants responsible for spoilage in honey. To address the signature volatile components of jujube honey contaminated by Zygosaccharomyces rouxii, headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and chemometrics analyses were used to analyze the variation of volatile substances during early contamination of mature and immature jujube honey. Undecanal, methyl butyrate, methyl 2-nonenoate, methyl hexanoate, and 2-methyl-3-pentanone were identified as signature volatiles of jujube honey contaminated with Z. rouxii. In addition, methyl heptanoate, 2,6,10-trimethyltetradecane, and heptanal were identified as potential volatile signatures for immature jujube honey. The R² and Q² of OPLS-DA analyses ranged from 0.736 to 0.955, and 0.991 to 0.997, which indicates that the constructed model was stable and predictive. This study has demonstrated that HS-SPME-GC-MS could be used to distinguish Z. rouxii-contaminated jujube honey from uncontaminated honey based on variation in VOCs, and could provide theoretical support for the use of HS-SPME-GC-MS for the rapid detection of honey decomposition caused by Z. rouxii, which could improve nutritional quality and reduce economic losses.

Aroma characterisation of Liu-pao tea based on volatile fingerprint and aroma wheel using SBSE-GC-MS

Liu-pao tea (LPT) has unique aroma characteristics, and is a special microbial fermented tea produced using dark raw tea (LPM) as its raw material. In this study, stir bar sorptive extraction (SBSE) combined with gas chromatography-mass spectrometry (GC-MS) was applied to investigate the volatiles of 16 LPTs and 6 LPMs. Moreover, variations in volatile profiles between LPTs and LPMs were explored. Results showed that a total of 132 volatile compounds were identified from LPTs. The volatile fingerprint was constructed with a similarity ranged from 0.85 to 0.99. Furthermore, twenty-six aroma compounds were selected to depict the molecular aroma wheel of LPT. Multivariate statistical analysis revealed that the contents of 24 aroma compounds changed significantly (P < 0.05) when LPMs were processed into LPTs. These results reveal the volatile profiles of LPTs and aroma composition changes during microbial fermentation process, which might provide chemical basis of the aroma quality of LPT.

Aroma correlation assisted volatilome coupled network analysis strategy to unveil main aroma-active volatiles of Rosa roxburghii

To investigate the main aroma-active volatiles out from comprehensive chemical profile, we proposed an aroma correlation assisted volatilome coupled network analysis strategy and applied it to the study of Rosa roxburghii. Based on 475 detected volatiles with GC × GC-TOF/MS analysis, the volatilome was screened with both positive aroma activities and high contents to discover some aliphatic acids, alcohols, aldehydes and esters, terpenoids as well as some alkenes and ketones. Especially, a series of homologous C6- and C8- acids, alcohols, aldehydes, esters as well as some terpenoids like limonene take the predominant contributions to the aromas. Moreover, two aroma-active and aroma-contributing volatile groups including acid-aldehyde-alcohol-ester and terpenoid groups were clustered to integrally be responsible for the major aromas of R. roxburghii with network analysis. Additionally, the accumulation of C6- and C8-family homologous aliphatic volatiles was also elucidated with linoleic and linolenic acid derived pathways. This strategy is practical to investigate the main aroma-active volatiles based on volatilome.

Dynamic change of the carotenoid metabolic pathway profile during oolong tea processing with supplementary LED light

Carotenoid-derived volatiles are important contributors to tea aroma quality. However, the profile of the carotenoid pathway and carotenoid-derived volatiles (CDVs) artificial regulation in oolong tea processing has yet to be investigated. In the present work, the content and varieties of carotenoid-derived volatiles, the genome-wide identification of carotenoid cleavage dioxygenase (CsCCD) gene family, the expression level of CsCCD and other key genes in the carotenoid pathway, and the profile of carotenoid substances were analyzed by multi-omics and bioinformatics methods with innovative postharvest supplementary LED light during oolong tea processing. The results showed that during oolong tea processing, a total of 17 CDVs were identified. The content of β-ionone increased up to 26.07 times that of fresh leaves and its formation was significantly promoted with supplementary LED light from 0.54 μg/g to 0.83 μg/g in the third turning over treatment. A total of 11 CsCCD gene family members were identified and 119 light response cis-acting regulatory elements of CsCCD were found. However, the expression level of most genes in the carotenoid pathway including CsCCD were reduced due to mechanical stress. 'Huangdan' fresh tea leaves had a total of 1 430.46 μg/g 22 varieties of carotenoids, which mainly composed of lutein(78.10%), β-carotene(8.24%) and zeaxanthin(8.18%). With supplementary LED light, the content of antherxanthin and zeaxanthin in xanthophyll cycle was regulated and CDVs such as α-ionone, β-ionone, pseudoionone, damascenone, 6,10-dimethyl-5,9-undecadien-2-one, citral, geranyl acetate and α-farnesene were promoted significantly in different phases during oolong tea processing. Our results revealed the profile of the carotenoid metabolism pathway in oolong tea processing from the perspective of precursors, gene expression and products, and put forward an innovative way to improve CDVs by postharvest supplementary LED light.

Enantiomeric separation and precise quantification of chiral volatiles in Wuyi rock teas using an efficient enantioselective GC × GC-TOFMS approach

Chiral volatiles play important roles in the formation of aroma quality of foods. To date, enantiomeric characteristics of chiral volatiles in Wuyi rock tea (WRT) and their aroma contributions are still unclear. In this study, an efficient enantioselective comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (Es-GC × GC-TOFMS) approach to separate and precisely quantitate 24 pairs of chiral volatiles in WRTs was established, and the enantiomeric distribution and aroma contribution of chiral volatiles among WRTs from four representative cultivars were investigated. Enantiomeric ratio (ER) of R-α-ionone (80%) in Dahongpao (DHP), ER of S-α-terpineol (57%) in Jinfo (JF), ERs of R-γ-heptanolactone (69%), S-γ-nonanolactone (55%), (2R, 5S)-theaspirane B (91%), concentration of S-(E)-nerolidol (313.37 ng/mL) in Rougui (RG) and concentration of R-α-ionone (33.01 ng/mL) in Shuixian (SX) were unique from other types of WRTs, which were considered as the potential chemical markers to distinguish WRT cultivars. The OAV assessment determined 7 volatile enantiomers as the aroma-active compounds, especially R-α-ionone and R-δ-octanolactone in SX, as well as S-(E)-nerolidol and (1R, 2R)-methyl jasmonate in RG contribute much to aroma formation of the corresponding WRTs. The above results provide scientific references for discrimination of tea cultivars and directed improvement of the aroma quality of WRT.

Characterization of volatile metabolites in Pu-erh teas with different storage years by combining GC-E-Nose, GC-MS, and GC-IMS

Storage time is one of the important factors affecting the aroma quality of Pu-erh tea. In this study, the dynamic changes of volatile profiles of Pu-erh teas stored for different years were investigated by combining gas chromatography electronic nose (GC-E-Nose), gas chromatography-mass spectrometry (GC-MS), and gas chromatography-ion mobility spectrometry (GC-IMS). GC-E-Nose combined with partial least squares-discriminant analysis (PLS-DA) realized the rapid discrimination of Pu-erh tea with different storage time (R2Y = 0.992, Q2 = 0.968). There were 43 and 91 volatile compounds identified by GC-MS and GC-IMS, respectively. A satisfactory discrimination (R2Y = 0.991, and Q2 = 0.966) was achieved by using PLS-DA based on the volatile fingerprints of GC-IMS. Moreover, according to the multivariate analysis of VIP > 1.2 and univariate analysis of p < 0.05, 9 volatile components such as linalool and (E)-2-hexenal were selected as key variables to distinguish Pu-erh teas with different storage years. The results provide theoretical support for the quality control of Pu-erh tea.

The aroma characteristics of oolong tea are jointly determined by processing mode and tea cultivars

This study delved into the aroma characteristics of "Qingxiang" oolong tea, analyzing six different cultivars and their processing modes. The findings showed that both cultivars and processing modes have a significant impact on the oolong tea aroma system. The study identified 18 terpenoid volatiles (VTs), 11 amino-acid-derived volatiles (AADVs), 15 fatty-acid-derived volatiles (FADVs), 3 carotenoid-derived volatiles (CDVs), and 10 other compounds in oolong tea that differentiate it from green and black tea. The turn-over stage was found to be the primary processing stage for oolong tea aroma formation. Molecular sensory analysis revealed that the "fresh" odor attribute is the basis for its aroma, while "floral and fruity" fragrances are its aroma characteristics. The perception of oolong tea as "fresh" and "floral and fruity" is influenced by the interactions of its aroma components. These findings provide a new basis for breed improvement and process enhancement in oolong tea production.

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.

GC-MS and LC-MS/MS metabolomics revealed dynamic changes of volatile and non-volatile compounds during withering process of black tea

High-performance liquid chromatography (HPLC), headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and ultra-high performance liquid chromatography-Q-Exactive HF-X mass spectrometer (UHPLC-Q-Exactive HF/MS) were carried out to reveal dynamic changes of volatile and non-volatile compounds during the withering process of black tea. A total of 118 volatile organic compounds (VOCs) and 648 metabolites were identified in fresh and withered tea-leaves, respectively. Among them, 47 VOCs (OAV > 1.0) for the aroma formation, and 46 characteristic metabolites (VIP > 1.50, p < 0.01) selected through orthonormal partial least squares-discriminant analysis, indicated the withering contribution during black tea processing. Overall, the withering promoted alcohols, aldehydes, phenols, heterocyclic oxygen, hydrocarbons and halogenated hydrocarbons through relevant hydrolyzation, decomposition, terpene synthesis, and O-methylation. The hydrolyzation, O-methylation, condensation and N-acylation of kaempferol glycosides, quercetin glycosides, ester catechins, and gallic acid generated the accumulation of methoxyl flavonoids and flavonoid glucosides, dihydrokaempferol, syringic acid, theaflavins, and N-acylated amino acids, respectively.

Soilless Cultivated Halophyte Plants: Volatile, Nutritional, Phytochemical, and Biological Differences

The use of halophyte plants appears as a potential solution for degraded soil, food safety, freshwater scarcity, and coastal area utilization. These plants have been considered an alternative crop soilless agriculture for sustainable use of natural resources. There are few studies carried out with cultivated halophytes using a soilless cultivation system (SCS) that report their nutraceutical value, as well as their benefits on human health. The objective of this study was to evaluate and correlate the nutritional composition, volatile profile, phytochemical content, and biological activities of seven halophyte species cultivated using a SCS (Disphyma crassifolium L., Crithmum maritimum L., Inula crithmoides L., Mesembryanthemum crystallinum L., Mesembryanthemum nodiflorum L., Salicornia ramosissima J. Woods, and Sarcocornia fruticosa (Mill.) A. J. Scott.). Among these species, results showed that S. fruticosa had a higher content in protein (4.44 g/100 g FW), ash (5.70 g/100 g FW), salt (2.80 g/100 g FW), chloride (4.84 g/100 g FW), minerals (Na, K, Fe, Mg, Mn, Zn, Cu), total phenolics (0.33 mg GAE/g FW), and antioxidant activity (8.17 µmol TEAC/g FW). Regarding the phenolic classes, S. fruticosa and M. nodiflorum were predominant in the flavonoids, while M. crystallinum, C. maritimum, and S. ramosissima were in the phenolic acids. Moreover, S. fruticosa, S. ramosissima, M. nodiflorum, M. crystallinum, and I. crithmoides showed ACE-inhibitory activity, an important target control for hypertension. Concerning the volatile profile, C. maritimum, I. crithmoides, and D. crassifolium were abundant in terpenes and esters, while M. nodiflorum, S. fruticosa, and M. crystallinum were richer in alcohols and aldehydes, and S. ramosissima was richer in aldehydes. Considering the environmental and sustainable roles of cultivated halophytes using a SCS, these results indicate that these species could be considered an alternative to conventional table salt, due to their added nutritional and phytochemical composition, with potential contribution for the antioxidant and anti-hypertensive effects.

The Cultivar Effect on the Taste and Aroma Substances of Hakka Stir-Fried Green Tea from Guangdong

The flavor and quality of tea largely depends on the cultivar from which it is processed; however, the cultivar effect on the taste and aroma characteristics of Hakka stir-fried green tea (HSGT) has received little attention. High-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), and sensory evaluations were used to detect and predict the essential taste and aroma-contributing substances of HSGTs made from Huangdan (HD), Meizhan (MZ) and Qingliang Mountain (QL) cultivars. Orthogonal partial least squares data analysis (OPLS-DA) ranked four substances that putatively distinguished the tastes of the HSGTs, epigallocatechin gallate (EGCG) > theanine > epigallocatechin (EGC) > epicatechin gallate (ECG). Ten substances with variable importance in projections (VIPs) ≥ 1 and odor activation values (OAVs) ≥ 1 contributed to their overall aromas, with geranylacetone having the most significant effect on HD (OAV 1841), MZ (OAV 4402), and QL (OAV 1211). Additionally, sensory evaluations found that HD was relatively equivalent to QL in quality, and both were superior to MZ. HD had a distinct floral aroma, MZ had a distinct fried rice aroma, and QL had a balance of fried rice and fresh aromas. The results provide a theoretical framework for evaluating the cultivar effect on the quality of HSGT and put forward ideas for future HSGT cultivar development.

Comparative studies of fermented coffee fruits post-treatments on chemical and sensory properties of roasted beans in Yunnan, China

In this study, medium roasted coffee with four different fermented coffee fruits post-treatments (dry, wet, semi-dry and hot air dry) was used as the material. Chemical profile and sensorial analysis were used to comprehensively analyze the effects of post-treatments on coffee flavor characteristics from multiple dimensions. A total of 31 water-soluble chemical components and 39 volatile compounds were identified in roasted coffee, and distinct post-treatments based on chemical orientation make coffee highly differentiated. In addition, the principal component analysis (PCA) of the chemical composition integrated data set showed that the first two principal components could explain 54.9% of the sample variability. All four post-treatments can be classified as "specialty coffees" according to the Specialty Coffee Association (SCA) protocol, with various organoleptic characteristics and flavor attributes. As a result, the fermented coffee fruits post-treatment method further determines the quality characteristics of coffee, thus meeting the needs of different niche markets.

Improving flavor of summer Keemun black tea by solid-state fermentation using Cordyceps militaris revealed by LC/MS-based metabolomics and GC/MS analysis

Cordyceps militaris (C. militaris) has been approved and widely used in healthy food. The present study aimed to improve the flavor of summer Keemun black tea (KBT) using C. militaris solid-state fermentation. Combined with sensory evaluation, the volatile and non-volatile components of solid-state fermentation of KBT (SSF-KBT) and KBT were analyzed. The results showed that after the solid-state fermentation, the contents of total polyphenol, total flavonoid, and total free amino acids were significantly reduced. Further non-targeted metabolomics analysis revealed that the contents of non-galloylated catechins and d-mannitol increased, while the galloylated catechins and flavonoid glycosides decreased as did the bitterness and astringency of KBT. Dihydro-β-ionone and β-ionone (OAV = 59321.97 and 8154.17) were the aroma-active compounds imparting woody and floral odors in SSF-KBT, respectively. Current study provides a new avenue to develop summer-autumn KBT.

Identification of Key Components Responsible for the Aromatic Quality of Jinmudan Black Tea by Means of Molecular Sensory Science

A fruity aroma is regarded as an important factor in the evaluation of black tea quality. However, the compounds contributing to a particularly fruity aroma still garner less attention. In this study, we aimed to identify the aroma-active compounds of the peach-like aroma of Jinmudan black tea (JBT). We used gas chromatography-mass spectrometry (GC-MS) to reveal the profile of the chemical compounds integrated into JBT and identified terpenoids, heterocyclic, and esters that contribute to its floral and fruity aroma. Under the PCA and PLS-DA modes, JBT and Fuyun NO. 6 black tea (FBT) can be divided into two classes, respectively (class 1 and class 2); several compounds, including indole, methyl salicylate, and δ-decalactone, have a higher VIP value (Variable Importance in Projection), and it has been found that δ-decalactone was the characteristic aromatic compound of peach fruit. Gas chromatography-olfactometry (GC-O) and the odor activity value (OAV) indicated that, in JBT, linalool, phenylacetaldehyde, and δ-decalactone could be considered aroma-active compounds (AACs). However, in FBT, the high content of heterocyclic compounds contribute to its caramel-like aroma. As for the biochemical compounds measurement, JBT has a higher content of theaflavins (TFs), thearubigins (TRs), and flavonoids. These results provide a theoretical basis for the quality and processing improvement in JBT.

Impact of Lavender Flower Powder as a Flavoring Ingredient on Volatile Composition and Quality Characteristics of Gouda-Type Cheese during Ripening

This study aimed to formulate a Gouda-type cheese from cow's milk, flavored with lavender flower powder (0.5 g/L matured milk), ripened for 30 days at 14 °C and 85% relative humidity. Physicochemical, microbiological, and textural characteristics, as well as the volatile composition of the control (CC-cheese without lavender) and lavender cheese (LC), were assessed at 10-day intervals of ripening. Consumers' perception, acceptance, and purchase intention were only evaluated for ripened cheeses. Moisture and carbohydrate contents, the pH, cohesiveness, indexes of springiness and chewiness decreased during ripening in both CC and LC; however, protein, ash, and sodium chloride contents, titratable acidity, hardness, lactobacilli, streptococci, and volatiles increased. Fat and fat in dry matter contents, respectively, the energy value did not vary with ripening time in LC and increased in CC; gumminess decreased in CC and did not change in LC. Lavender flower powder significantly affected the cheese's microbiological and sensory characteristics and volatile composition but did not considerably impact physicochemical and textural ones. Populations of lactobacilli and streptococci were substantially higher in LC compared to CC. The volatile profile of LC was dominated by terpene and terpenoids, and that of CC by haloalkanes. Sensory scores were slightly lower for LC than CC, even if it did not considerably affect consumers' acceptance and purchase intention.

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.

Effects of processing procedures on the formation of aroma intensity and odor characteristic of Benshan tea (Oolong tea, Camellia sentences)

Benshan tea is a kind of oolong tea, and Benshan (Camellia sinensis) tea tree originates from Anxi County of Fujian Province in China, which is a national tea tree breed. Tea processing is the key to the formation of its odor characteristics. It is extremely important to step by step analyze effects of tea processing on aroma intensity and the formation of odor characteristics for optimizing tea processing process and improving tea quality. The results of this study showed that processing resulted in a significant increase in the content of volatile compounds in tea leaves, i.e., from 25.213 μg/kg to 111.223 μg/kg, in which the volatile compounds were mainly terpenoids. Secondly, the analysis found that 20 kinds of key compounds constituted to odor characteristics of Benshan tea leaves, among which geraniol, trans-β-ionone, gerol, citronellol, benzeneacetaldehyde, and trans-nerolidol were the most key six. Floral and fruity aromas, especially floral aroma, mainly formed odor characteristics of Benshan tea after processing, while floral aroma mainly came from the contribution of geraniol, which was the foremost compound in the formation of floral aroma of Benshan tea.

Oolong tea of different years protects high-fat diet-fed mice against obesity by regulating lipid metabolism and modulating the gut microbiota

Long-term stored oolong tea has recently attracted considerable attention concerning its salutary effect. In this study, the anti-obesity effect of different years' oolong tea on high-fat diet-fed mice was compared. Wuyi rock tea of 2001, 2011, and 2020 were chosen to be the representative samples of oolong tea. The results showed that eight-week administration of 2001 Wuyi rock tea (WRT01), 2011 Wuyi rock tea (WRT11), and 2020 Wuyi rock tea (WRT20) extracts (400 mg per kg per d) significantly decreased the body weight and attenuated the obesity in high-fat diet-fed mice. 2001 and 2011 Wuyi rock teas reduced obesity mainly through regulating lipid metabolism and activating the AMPK/SREBP-1 pathway, downregulating the expression of SREBP-1, FAS, and ACC and upregulating CPT-1a expression; while the 2011 and 2020 Wuyi rock teas by moderating the gut microbiota dysbiosis, reshaping the gut microbiota, and promoting the growth of beneficial bacteria, especially Akkermansia. 2011 Wuyi rock tea was proven to be more effective in reducing body weight gain and liver oxidative stress than the others. Collectively, all three Wuyi rock teas of different years alleviated high-fat diet-induced obesity by regulating lipid metabolism and modulating gut microbiota, whereas the emphasis of their internal mechanism is different with different storage ages.

Variations of main quality components of matcha from different regions in the Chinese market

Matcha has a unique aroma of seaweed-like, which is popular with Chinese consumers. In order to effectively understand and use matcha for drinks and tea products, we roundly analyzed the variation of main quality components of 11 matcha samples from different regions in the Chinese market. Most of matcha samples had lower ratio of tea polyphenols to amino acids (RTA), and the RTA of 9 samples of matcha was less than 10, which is beneficial to the formation of fresh and mellow taste of matcha. The total volatile compounds concentrations by HS-SPME were 1563.59 ~ 2754.09 mg/L, among which terpenoids, esters and alcohols were the top three volatile components. The total volatile compounds concentrations by SAFE was 1009.21 ~ 1661.98 mg/L, among which terpenoids, heterocyclic compounds and esters ranked the top three. The 147 volatile components with high concentration (&gt;1 mg/L) and no difference between samples are the common odorants to the 11 samples of matcha. The 108 distinct odorants had differences among the matcha samples, which were important substances leading to the different aroma characteristics. Hierarchical cluster analysis (HCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) showed that 11 samples of matcha were well clustered according to different components. Japanese matcha (MT, MY, ML, MR, MJ) could be clustered into two categories. The aroma composition of Guizhou matcha (GM1, GM2) was similar to that of Japanese matcha, 45 volatile components (decanal, pyrazine, 3,5-diethyl-2-methyl-, 1-hexadecanol, etc. were its characteristic aroma components. The aroma characteristics of Shandong matcha and Japanese matcha (ML, MR, MJ) were similar, 15 volatile components (γ-terpinene, myrtenol, cis-3-hexenyl valerate, etc.) were its characteristic aroma components. While Jiangsu matcha and Zhejiang matcha have similar aroma characteristics due to 225 characteristic aroma components (coumarin, furan, 2-pentyl-, etc). In short, the difference of volatile components formed the regional flavor characteristics of matcha. This study clarified the compound basis of the flavor difference of matcha from different regions in the Chinese market, and provided a theoretical basis for the selection and application of matcha in drinks and tea products.

Monitoring the baking quality of Tieguanyin via electronic nose combined with GC-MS

Roasting is extremely important for Tieguanyin oolong tea production because it strongly affects its chemical composition and sensory quality. In addition, there were significant differences in the preference for roasted tea among different people. However, the effect of roasting degree on the aroma characteristics and flavor quality of Tieguanyin tea is still unclear. To further study this, an electronic nose combined with gas chromatography-mass spectrometry (GC-MS) was used to monitor the baking process of Tieguanyin. The physicochemical indexes, sensory quality, and odor characteristics of the tea leaves subjected to different roasting conditions were measured. The increase in the roasting degree caused a decrease in the amount of taste substances such as tea polyphenols, catechins, and amino acids and a sharp increase in the phenol to ammonia ratio. Sensory evaluation results showed that moderate roasting could help improve the quality of the tea leaves. The results obtained using the electronic nose and GC-MS showed that there were substantial differences in the volatile substances, and 103 flavor compounds were highly correlated with the aroma characteristics of roasted tea with different roasting degrees. In addition, the electronic nose combined with various classification models could better distinguish tea leaves with different roasting degrees. Among them, the accuracy of the RF training set and prediction set reached>98.44%. The results of this study will aid in comprehensively monitoring the effects of the baking process on the flavor, chemical composition, and aroma of Tieguanyin as well as in distinguishing Tieguanyin tea leaves with different qualities.

Identification of volatile compounds and metabolic pathway during ultrasound-assisted kombucha fermentation by HS-SPME-GC/MS combined with metabolomic analysis

The current work combines headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC/MS) with multivariate analysis fusion metabonomics for examining metabolite profile changes. The correlation with metabolic pathways during the fermentation of kombucha tea were comprehensively explored. For optimizing the fermentation process, ultrasound-assisted factors were explored. A total of 132 metabolites released by fermented kombucha were detected by HS-SPME-GC/MS. We employed the principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) to present the relationship between aroma components and fermentation time, of which the first two principal components respectively accounted for 60.3% and 6.5% of the total variance. Multivariate statistical analysis showed that during the fermentation of kombucha tea, there were significant differences in the phenotypes of metabolites in the samples, and 25 characteristic metabolites were selected as biomarkers. Leaf alcohol was first proposed as the characteristic volatile in the fermentation process of kombucha. Furthermore, we addressed the generation pathways of characteristic volatiles, their formation mechanisms, and the transformational correlation among them. Our findings provide a roadmap for future kombucha fermentation processing to enhance kombucha flavor and aroma.

Chemical Profile and Hematoprotective Activity of Artisanal Jabuticaba (Plinia jabuticaba) Wine and Derived Extracts

The alcoholic fermentation of jabuticaba berries (Plinia spp.) originates from a beverage with an intense taste and aroma, popularly known as jabuticaba wine (JW). In addition, polyphenols transferred from fruit peels to the final product turn this beverage into a promising source of bioactive agents. Here, the chemical profile and antioxidant potential of artisanal JW and derivative extracts were determined. Volatile organic compounds were determined by HS-SPME/GC-MS analysis. The wine was dried by lyophilization and subjected to liquid-liquid partitioning (water: ethyl acetate), resulting in three fractions (JWF1-3). ABTS•+ and DPPH•+ scavenging assays were performed to evaluate the antioxidant capacity. In addition, the extracts’ hematoprotective activity was evaluated against oxidative stress. Finally, the extracts were analyzed by LC-HRMS/MS. HS-SPME/GC-MS analysis highlighted 1,8-cineole as the main compound that contributes to the camphor/mint flavor. JWF2 and JWF3 displayed the highest antioxidant capacity. JWF2 stood out for preventing oxidative damage in red blood cells at 7.8 µg·mL−1 The maximal protection of ascorbic acid occurred at 8.8 µg·mL−1. The LC-HRMS/MS analysis allowed the annotation of seventeen compounds, most of them with recognized antioxidant activity such as anthocyanins, catechins, flavanols, and phenolic acids. The results presented herein reinforce JW as a pleasant beverage with bioactive potential.

Aroma characteristics of Wuyi rock tea prepared from 16 different tea plant varieties

Wuyi rock tea (WRT) is famous for its long history and unique characteristic of floral, fruity and nutty flavors. This study investigated the aroma characteristics of WRTs prepared from 16 different oolong tea plant varieties. The sensory evaluation results showed that all WRTs had an 'Yan flavor' taste, and the odor was strong and lasting. Roasted, floral and fruity odors were the prime aroma profiles for WRTs. Furthermore, a total of 368 volatile compounds were detected using HS-SPME-GC-MS and analyzed with OPLS-DA and HCA methods. The volatile compounds heterocyclic compounds, esters, hydrocarbons, terpenoids and ketones were the major aromatic components of the WRTs. Specifically, the volatile profiles among newly selected cultivars were comparatively analyzed, and 205 differential volatile compounds were found with variable importance in the projection (VIP) values above 1.0. These results indicated that the aroma profiles of WRTs were mainly dependent on the cultivar specificities of volatile compounds.

Comparative study of the volatile fingerprints of roasted and unroasted oolong tea by sensory profiling and HS-SPME-GC-MS

Roasting plays important roles in shaping the volatile profile of oolong tea. In this study, the sensory attributes and volatile compositions of 153 roasted or unroasted oolong tea samples, belonging to four typical types, namely, High Mountain oolong tea (HMT), Tieguanyin tea (TGYT), Dongding oolong tea (DDT) and Wuyi rock tea (WRT), were studied in detail. Based on the sensory evaluation by tea evaluation experts, their respective sensory profiles were established and compared. Unroasted teas had more pronounced fresh and green flavors, while roasted teas had higher scores in pungent and caramel flavors. In particular, WRT demonstrated a unique fragrance of floral fruity flavors. By using HS-SPME-GC-MS analysis, a total of 128 compounds were identified across all samples. Notably, it was found that roasting largely increased the variety of volatile compounds in oolong tea. Furthermore, the characteristic volatile compounds of each type of tea were identified by PLS-DA modeling. Linalool and geraniol were the characteristic volatiles of HMT. Four volatiles, including (E)-nerolidol, jasmin lactone, benzeneacetaldehyde, and 4-methyl benzaldehyde oxime were identified as the characteristic volatiles of TGYT. Seven volatiles, including N-ethyl pyrrole, 3-(hydroxy methyl) pyridine, 4-pyridylcarbinol, 1-methyl pyrrole-2-carboxaldehyde, 2-ethyl-3,5-dimethyl pyrazine, 4-amino-2,3-xylenol, and 4,6-dimethyl pyrimidine were the characteristic volatiles of DDT. For WRT, 2,2,6-trimethyl cyclohexan-1-one, hexanoic acid, benzaldehyde, benzyl alcohol, β-cyclocitral, (E)-β-ionone, α-ionone, and octanoic acid were the characteristic volatiles. These findings expand our knowledge of the volatile fingerprints of oolong tea.

Elucidating the effects of Lactobacillus plantarum fermentation on the aroma profiles of pasteurized litchi juice using multi-scale molecular sensory science

Three Lactobacillus Plantarum (LP), namely LP28, LP226 and LPC2W, were employed to investigate the effect on the aroma profiles of pasteurized litchi juice using E-nose, GC-IMS, GC-MS, and sensory evaluation. The E-nose results showed that pasteurization weakened the flavor profile of litchi juice, while LP fermentation effectively promoted flavor formation. The GC-MS analysis demonstrated that pasteurization significantly reduced the content of alcohols (28.51%), especially geraniol and citronellol, which give litchi juices a fruity and floral aroma. Different LP fermentation enhances the characteristic aroma and produces some new compounds that give it a strong fruity and citrus-like aroma. Moreover, 37 aroma-active compounds (OAV>1) indicated that the linalool (OAV 7504) was the highest, followed by (Z)-rose oxide (OAV 4265), 1-octen-3-ol (OAV 1055) and geraniol (OAV 764), which jointly form the main characteristic flavor. More esters were identified by GC-IMS, indicating the advantage of the combined approach for a better understanding of the impact of pasteurization and fermentation on the litchi juice. The sensory evaluation confirmed that the aroma attributes of fruity, citrus-like, floral, sweet and litchi-like were stronger for the samples fermented by LP28 than those for the other samples. The combination strategy used in this study would facilitate the awareness of litchi juice aroma and broaden our insight into the deep processing of litchi.

Chemical and nutritional characterization of Ambelania duckei (Apocynaceae) an unexplored fruit from the Amazon region

Ambelania duckei Markgr is a species of the Apocynaceae family, native to the Amazon region that is unexplored from a nutritional point of view and studied in relation to its chemical constituents. This work presents an unprecedented study of the proximate composition, lipid profile, a chromatographic analysis, and the antioxidant activity of extracts obtained from the pulp, peel and seeds of the fruit. The results showed that potassium, calcium, and magnesium stood out as the most abundant key minerals in the fruit peel and pulp, with an emphasis on the potassium present in the fruit pulp at 1750.0 mg/100 g. The peel had the highest content of total phenolics (374.86 mg/g), flavonoids (15.54 mg/g), tannins (27.45 mg/g) and O-diphenols (379.36 mg/g; 645.71 mg/g). The antioxidant activity (AA) was highest in the peel compared to the pulp in the DPPH, ABTS, and ORAC tests showing: IC₅₀ of 29.82; 43.67; and 407.13 µg/mL, respectively but a lower activity for the Fe²⁺ chelator. The analysis of the lipid fractions from the peel, pulp, and seeds of the A. duckei fruit resulted in 14 types of fatty acids. The major fatty acids found in the three parts of the fruit were oleic acid (peel, 22.52 %), palmitic acid (pulp, 17.34 %), and linoleic acid (seeds, 47.99 %). The lipid profile and nutritional aspects had a PUFA/SFA ratio (0.4-1.8) in the different parts of the A. duckei fruit; the atherogenic and thrombogenic indexes were higher in the peel (1.23) and pulp (0.62), respectively. The ratio between the hypocholesterolemic and hypercholesterolemic fatty acids (0.5 - 3.8) calculated for the fruit are within the desirable range for a nutritious food. The chromatographic analysis of the volatile organic compounds (VOCs) from the peel and pulp of the fruit, identified 74 VOCs, of which 60.9 % are related to terpenes, and emit notes such as cucumber, green, fatty, floral, and mint, due to the presence of substances with OAVs > 10, especially α-ionone, 1,8-cineole, 2,4-decadienal, and dodecanal. The analysis of the MS and MS/MS spectra of the chromatograms obtained by LC- QTOF-HRMS led to the identification of 26 compounds in the peel, seeds and pulp of A. duckei, such as fatty acids, phenolic acid, flavonoids, proanthocyanidins, alkaloids, and terpenoids. The results show that the pulp of A. duckei has potential as nourishing food and the nutritional and chemical aspects of the peel can be applied to commercial applications.

Characterization of the Key Aroma Compounds in Different Aroma Types of Chinese Yellow Tea

Yellow tea is one of the six major tea categories in China. The floral fragrance type, high-fired fragrance type, fresh fragrance type, and corn-like fragrance type were the main aroma types of yellow tea screened by QDA. A total of 103 volatiles were identified in yellow teas by HS-SPME/GC-MS analysis. Using multivariate analysis and OAVs, forty-seven aroma compounds were identified as key aroma compounds for the formation of different aroma types of yellow teas. Among them, 8, 14, 7, and 18 key aroma compounds played an important role in the formation of aroma characteristics of floral fragrance, high-fired fragrance, fresh fragrance, and corn-like fragrance types of yellow teas, respectively. Furthermore, PLS analysis revealed that 12 aroma compounds were the key contributors to the 'floral and fruity' and 'sweet' attributes, five aroma compounds contributed to the 'roasted' attribute, and four aroma compounds related to the 'fresh' and 'grassy' attributes. This study provides new insights into the aroma characteristics formation of different aroma types of yellow teas and will provide a valuable theoretical basis for improving the flavor quality of yellow tea during the manufacturing process.

Insights into Characteristic Volatiles in Wuyi Rock Teas with Different Cultivars by Chemometrics and Gas Chromatography Olfactometry/Mass Spectrometry

Wuyi rock tea (WRT) is one of the most famous subcategories of oolong tea, exhibiting distinct aroma characteristics with the application of different cultivars. However, a comprehensive comparison of the characteristic volatiles among WRTs with different cultivars has rarely been carried out. In this study, non-targeted analyses of volatile fragrant compounds (VFCs) and targeted aroma-active compounds in WRTs from four different cultivars were performed using chemometrics and gas chromatography olfactometry/mass spectrometry (GC-O/MS). A total of 166, 169, 166, and 169 VFCs were identified for Dahongpao (DHP), Rougui (RG), Shuixian (SX), and Jinfo (JF), respectively; and 40 components were considered as the key differential VFCs among WRTs by multivariate statistical analysis. Furthermore, 56 aroma-active compounds were recognized with predominant performances in "floral & fruity", "green & fresh", "roasted and caramel", "sweet", and "herbal" attributes. The comprehensive analysis of the chemometrics and GC-O/MS results indicated that methyl salicylate, p-cymene, 2,5-dimethylpyrazine, and 1-furfurylpyrrole in DHP; phenylethyl alcohol, phenethyl acetate, indole, and (E)-β-famesene in RG; linalool, phenethyl butyrate, hexyl hexanoate, and dihydroactinidiolide in JF; and naphthalene in SX were the characteristic volatiles for each type of WRT. The obtained results provide a fundamental basis for distinguishing tea cultivars, recombination, and simulation of the WRT aroma.