Determination of nerolidol in teas using headspace solid phase microextraction-gas chromatography

Effect of moisture loss on aroma profile, key odorants, and fatty acids of Amomum tsaoko during vacuum oven drying

The effects of vacuum oven drying at 60 °C on the aroma profile, key odorants, fatty acids, and chiral compounds of fresh Amomum tsaoko (AT) were evaluated over varying drying times. Quantitative descriptive analysis, solvent-assisted flavor evaporation, and gas chromatography-olfactometry-mass spectrometry identified and quantitated 36 odor-active compounds. Aldehydes, particularly geranial (1606-1809 mg/kg), were consistently prominent across all drying durations. Twenty-four key odorants with odor activity values greater than one were identified and screened. Relationships among seven samples, 24 key odorants, and six attributes were elucidated through orthogonal partial least squares-discriminant analysis. Notably, 13 odorants exhibited changes during the drying process, as indicated by variable importance for projection scores. Additionally, fatty acid analyses revealed that palmitic and oleic acids were predominant in AT. This study provides valuable insights into the impact of moisture loss on the key chemical components of AT, supporting the development of diverse consumer-oriented products.

Review of Recent Advances in Microbial Production and Applications of Nerolidol

Nerolidol, an oxygenated sesquiterpene (C15H26O) that occurs in plants, exhibits significant bioactivities such as antioxidant, anti-inflammatory, antimicrobial, and neuroprotective activities. It is a U.S. Food and Drug Administration-approved flavoring agent and a common ingredient in several commercial products such as toiletries and detergents. In addition, the potential applications of nerolidol that may prove beneficial for human health, agriculture, and the food industry have garnered increasing attention from researchers in these fields. Recent years have witnessed the application of metabolic engineering and synthetic biology strategies for constructing microbial cell factories that can produce nerolidol, which is considered a sustainable and economical approach. This review summarizes recent research on the biological activities and applications of nerolidol as well as nerolidol production using microbial cell factories. In addition, the synthesis of bioactive derivatives of nerolidol is addressed. In summary, this review provides readers with an updated understanding of the potential applications and green production prospects of nerolidol.

Integrated metabolome and transcriptome analysis provides insights into the mechanisms of terpenoid biosynthesis in tea plants (Camellia sinensis)

Volatile terpenoids are major substances responsible for the floral and fruity scents of teas. However, little is known about the regulatory mechanisms of terpenoid biosynthesis pathways in tea plants. 'Zhenfeng Yesheng tea' (ZFYS), a distinctive tea tree germplasm resource in Guizhou province, is known for its unique flavor characterized by a mellow taste and a floral aroma. Here, we conducted metabolome and transcriptome analyses of 'ZFYS', 'Jinguanyin tea' (JGY), and 'Longjing 43 tea' (LJ43) leaves to obtain the global correlation of MYB TFs with terpene synthase (TPS) genes and differential accumulated metabolites. In total, 292 differentially accumulated metabolites (DAMs) were identified and chemically classified, with 26.37% of them being terpenoids. Among these, 33 key volatile terpenoids significantly accumulated in 'ZFYS', 'LJ43', and 'JGY' leaves, mainly contributing to the floral and sweet scents. In addition, a total of 6330, 7238, and 8557 unigenes were obtained in "JGY vs LJ43", "ZFYS vs JGY", and "ZFYS vs LJ43" comparisons, respectively. The results of transcriptome analysis, correlation analysis, and quantitative real-time PCR (qRT-PCR) analysis revealed significant correlations between candidate CsTPSs and CsMYBs. The expression levels of CsMYB59, CsMYB167 and CsMYB178 showed that they had a strong positive correlation with CsTPS01, -03, -15, -53, -69 and -79, suggesting their potential function in regulating sesquiterpenoid biosynthesis. In conclusion, this study provides comprehensive metabolomics and transcriptomics profiles of the germplasm of 'ZFYS' tea plants and reveals the underlying key genes involved in volatile terpenoid biosynthesis.

Characterization of volatile compounds and identification of key aroma compounds in different aroma types of Rougui Wuyi rock tea

In this study, we characterized the aroma profiles of different Rougui Wuyi rock tea (RGWRT) aroma types and identified the key aroma-active compounds producing these differences. The roasting process was found to have a considerable effect on the aroma profiles. Eleven aroma compounds, including linalool, β-ionone, geraniol, indole, and (E)-nerolidol, strongly affected the aroma profiles. An RGWRT aroma wheel was constructed. The rich RGWRT aroma was found to be dominated by floral, cinnamon-like, and roasty aromas. Human olfaction was correlated with volatile compounds to determine the aromatic characteristics of these compounds. Most key aroma-active compounds were found to have floral, sweet, and herbal aromas (as well as some other aroma descriptors). The differences in key compounds of different aroma types were found to result from the methylerythritol phosphate, mevalonic acid and shikimate metabolic pathways and the Maillard reaction. Linalool, geraniol, and (E,E)-2,4-heptadienal were found to spontaneously bind to olfactory receptors.

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.

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.

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.

Comparative analysis of Fenghuang Dancong, Tieguanyin, and Dahongpao teas using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry and chemometric methods

Fenghuang Dancong, Tieguanyin, and Dahongpao teas are belonged to semi-fermented oolong teas and are famous for their unique aroma. However, reports regarding the systematic comparison, differentiation, and classification of the volatile components of these three types of oolong teas are lacking. In this study, we aimed to establish a method for distinguishing these three types of oolong teas. The volatile components in a total of 21 tea samples of these three types of oolong teas were extracted, determined, and identified by headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS). In addition, chemometric methods such as hierarchical cluster analysis (HCA), principal component analysis (PCA), and orthogonal partial least squares discriminant analysis (OPLS-DA) were used for distinguishing and classifying the three types of oolong teas on the basis of the similarities and differences in the volatile components. The results showed that 125 volatile components were extracted and identified from the three types of oolong teas, among which 53 volatile components overlapped among the samples. The results of HCA indicated that the samples of each of the three types of oolong teas could be placed in one category when the t value was 220. The results of PCA and OPLS-DA showed that the volatile components such as dehydrolinalool, linalool oxide II, linalool, α-farnesene, linalool oxide I, β-ocimene, nerolidol, cis-3-butyric acid folate, myrcene, and (Z)-hexanoic acid-3-hexenyl ester are the characteristic components, which can be used to distinguish the three types of oolong teas. We developed a simple, fast, and efficient method for distinguishing three types of oolong teas and provided a feasible technique for the identification of oolong tea types.

Involvement of histone deacetylase CsHDA2 in regulating (E)-nerolidol formation in tea (Camellia sinensis) exposed to tea green leafhopper infestation

Herbivore-induced plant volatiles (HIPVs) help the tea plant (Camellia sinensis) adapt to environmental stress, and they are also quality-related components of tea. However, the upstream mechanism regulating the herbivore-induced expression of volatile biosynthesis genes is unclear, especially at the level of epigenetic regulation. In this study, similar to the effects of a tea green leafhopper infestation, treatments with exogenous jasmonic acid (JA) and histone deacetylase inhibitors significantly increased the (E)-nerolidol content in tea and induced the expression of the associated biosynthesis gene CsNES. Furthermore, a key transcription factor related to JA signaling, myelocytomatosis 2 (CsMYC2), interacted with histone deacetylase 2 (CsHDA2) in vitro and in vivo. A tea green leafhopper infestation inhibited CsHDA2 expression and decreased CsHDA2 abundance. Moreover, the tea green leafhopper infestation increased H3 and H4 acetylation levels in the promoter region of CsNES, which in turn upregulated the expression of CsNES and increased the (E)-nerolidol content. In this study, we revealed the effects of histone acetylations on the accumulation of HIPVs, while also confirming that CsHDA2-CsMYC2 is an important transcriptional regulatory module for the accumulation of (E)-nerolidol induced by tea green leafhoppers. The results of this study may be useful for characterizing plant aromatic compounds and the main upstream stress-responsive signaling molecules. Furthermore, the study findings will assist researchers clarify the epigenetic regulation influencing plant secondary metabolism in response to external stress.

Aromatic Profiles and Enantiomeric Distributions of Chiral Volatile Compounds in Pu-Erh Tea

Pu-Erh tea, as a typical post-fermented tea, can be divided into raw Pu-Erh tea (RAPT) and ripened Pu-Erh tea (RIPT) according to the processing technology. It is famous for its unique aroma after aging. Although previous research on the aroma characteristics of Pu-Erh tea mostly focused on the aroma compounds, little research on chiral compounds in RAPT and RIPT has been performed. Therefore, the current work aims to explore the aroma characteristics of Pu-Erh tea from the perspective of enantiomers of chiral compounds. A total of 15 enantiomers were determined in this study, among which (R)-(-)-2,2,6-trimethylcyclohexanone, (R)-(-)-linalool, (S)-(+)-linalool, (R)-(+)-δ-octanolactone, (R)-(+)-γ-nonanolactone, (2R,5R)-(+)-theaspirone A, and (R)-(-)-dihydroactinidiolide were identified as enantiomeric compounds that play an important role in the aroma of RAPT and RIPT. Furthermore, (2S,5R)-trans-linalool oxide and (R)-(+)-α-terpineol were important contributors to the aroma profile of RAPT, while (S)-(+)-2-methylbutanal, (S)-(-)-limonene, S-(-)-α-terpineol, and (1R,2R)-(-)-methyl jasmonate contributed to the characteristic aroma of RIPT. The addition of these enantiomeric compounds brings the aroma closer to that of the original tea sample. In addition, the analysis of chiral enantiomers of linalool, limonene, theaspirone A, and γ-nonanolactone can provide guidance for the quality and flavor control of Pu-Erh tea aroma.

Alternative Splicing and Its Roles in Plant Metabolism

Plant metabolism, including primary metabolism such as tricarboxylic acid cycle, glycolysis, shikimate and amino acid pathways as well as specialized metabolism such as biosynthesis of phenolics, alkaloids and saponins, contributes to plant survival, growth, development and interactions with the environment. To this end, these metabolic processes are tightly and finely regulated transcriptionally, post-transcriptionally, translationally and post-translationally in response to different growth and developmental stages as well as the constantly changing environment. In this review, we summarize and describe the current knowledge of the regulation of plant metabolism by alternative splicing, a post-transcriptional regulatory mechanism that generates multiple protein isoforms from a single gene by using alternative splice sites during splicing. Numerous genes in plant metabolism have been shown to be alternatively spliced under different developmental stages and stress conditions. In particular, alternative splicing serves as a regulatory mechanism to fine-tune plant metabolism by altering biochemical activities, interaction and subcellular localization of proteins encoded by splice isoforms of various genes.

Salting-out re-distillation combined with sensory-directed analysis to recover odor-active compounds for improving the flavor quality of instant Pu-erh tea

The objective of this study was to develop an effective recovery technology of odor-active compounds (OACs) to improve the flavor quality of instant Pu-erh tea (IPT) based on their released behaviors. Salting-out re-distillation (SRD) combined with sensory-directed analysis was developed. The contributing factors, including the soaking time of tea, recovery volume of condensed water of first distillation, amount of sodium chloride, recovery volume of condensed water of SRD, and re-use times of sodium chloride, were studied systematically. Under optimized conditions, 41 OACs were recovered in the first distillation, and the total recovery rate was 83.94%. Forty-one OACs were recovered via SRD, and the total recovery rate reached 72.29%, significantly better than membrane method (33.46%). The IPT prepared by adding OACs that recovered via SRD showed strong aroma attributes intensities and good coordination. This developed method can provide a more effective scheme to improve the flavor quality of IPT.

Comparative Analysis of Volatile Compounds in Tieguanyin with Different Types Based on HS-SPME-GC-MS

Tieguanyin (TGY) is one kind of oolong tea that is widely appreciated for its aroma and taste. To study the difference of volatile compounds among different types of TGY and other oolong teas, solid-phase microextraction−gas chromatography−mass spectrometry and chemometrics analysis were conducted in this experiment. Based on variable importance in projection > 1 and aroma character impact > 1, the contents of heptanal (1.60−2.79 μg/L), (E,E)-2,4-heptadienal (34.15−70.68 μg/L), (E)-2-octenal (1.57−2.94 μg/L), indole (48.44−122.21 μg/L), and (E)-nerolidol (32.64−96.63 μg/L) in TGY were higher than in other varieties. With the increase in tea fermentation, the total content of volatile compounds decreased slightly, mainly losing floral compounds. Heavily fermented tea contained a higher content of monoterpenoids, whereas low-fermentation tea contained higher contents of sesquiterpenes and indole, which could well distinguish the degree of TGY fermentation. Besides, the volatiles analysis of different grades of TGY showed that the special-grade tea contained more aroma compounds, mainly alcohols (28%). (E,E)-2,4-Heptadienal, (E)-2-octenal, benzeneacetaldehyde, and (E)-nerolidol were the key volatile compounds to distinguish different grades of TGY. The results obtained in this study could help enrich the theoretical basis of aroma substances in TGY.

Characterization of key aroma compounds and enantiomer distribution in Longjing tea

By comparing the enantiomers of authentic Longjing tea, the authenticity of Longjing tea can be effectively distinguished. In this study, 18 enantiomers were identified using a chiral column. At the same time, the unique enantiomer ratio (ER) of Longjing tea (LG1, LG2, LG3, LG4, LG5) of different grades and origins was determined. The ER can provide a theoretical basis for distinguishing Longjing tea of different grades and origins, and for identifying the authenticity of Longjing tea. The ER ratio of (R)-(-)-1-octen-3-ol and (S)-(+)-1-octen-3-ol can be used to identify LG1 (71:29). The ER ratio of (S)-(+)-α-ionone and (R)-(-)-α-ionone can be used to identify LG2 (65:35). The ER ratio of (R)-(-)-dihydroactinidiolide to (S)-(+)-dihydroactinidiolide (71:29) can also be used to detect LG3. The ER ratio of (R)-(+)-Limonene and (S)-(-)-limonene can be used to identify LG4 (20:80). The ER ratio of (R)-(-)-linalool to (S)-(+)-linalool (12:83) was available to identify LG5.

Roasting process shaping the chemical profile of roasted green tea and the association with aroma features

Roasting process impacts the chemical profile and aroma of roasted tea. To compare the impacts of far-infrared irradiation and drum roasting treatments (light, medium and heavy degrees), the corresponding roasted teas were prepared from steamed green tea for chemical analyses and quantitative descriptive analysis on aroma, and correlations between volatiles and aroma attributes were studied. There were 8 catechins, 13 flavonol glycosides and 105 volatiles quantified. Under heavy roasting treatments, most catechins and flavonol glycosides decreased, and aldehydes, ketones, furans, pyrroles/pyrazines, and miscellaneous greatly increased, while far-infrared irradiated teas had distinct nutty aroma compared with the roasty and burnt odor of drum roasted teas. The weighted correlation network analysis result showed that 56 volatiles were closely correlated with the aroma attributes of roasted teas. This study reveals the differential chemical and sensory changes of roasted teas caused by different roasting processes, and provides a novel way for flavor chemistry study.

Identification and similarity analysis of aroma substances in main types of Fenghuang Dancong tea

Fenghuang Dancong tea covers the oolong tea category and is widely acknowledged for its unique floral and honey flavor. In order to characterize the volatile components in nine different aroma types of Fenghuang Dancong tea, the Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC- MS) were employed. In addition, the similarity analysis and cluster analysis (CA) were performed to compare the aroma characteristics and establish the correlation between the nine types of teas. The principal component analysis (PCA) and orthogonal partial least squares discrimination analysis (OPLS-DA) method were employed to determine the volatile components with a high contribution to the overall aroma of each type of tea. The results presented a total of 122 volatile aroma components including 24 kinds of alcohol, 23 kinds of esters, 15 kinds of olefins, 12 kinds of aldehydes, 12 kinds of ketones, 13 kinds of alkanes and 23 kinds of other components from the nine types of Fenghuang Dancong tea. Of these volatile aroma components, 22 types were common with linalool, dehydrolinalool, linalool oxide I, linalool oxide II, etc. The similarity of the nine types of Fenghuang Dancong tea was found between 46.79% and 95.94%. The CA indicated that the nine types of Fenghuang Dancong tea could be clustered into four categories when the ordinate distance reached to 10. The PCA demonstrated that decane, octadecane, 2,2,4,6,6-pentamethylheptane, dehydrolinalool, geraniol and nerol were the important aroma components to Fenghuang Dancong Tea. OPLS-DA proved that 2,2,4,6,6-pentamethylheptane, dehydrolinalool, phenylacetaldehyde, nerolidol, linalool oxide I and hexanal were the key differential compounds between the various types of tea samples. This study provides a theoretical basis for characterizing the volatile aroma components in the main types of Fenghuang Dancong tea as well as the similarity and correlation between various types of Fenghuang Dancong tea.

Green Approaches to Sample Preparation Based on Extraction Techniques

Preparing a sample for analysis is a crucial step of many analytical procedures. The goal of sample preparation is to provide a representative, homogenous sample that is free of interferences and compatible with the intended analytical method. Green approaches to sample preparation require that the consumption of hazardous organic solvents and energy be minimized or even eliminated in the analytical process. While no sample preparation is clearly the most environmentally friendly approach, complete elimination of this step is not always practical. In such cases, the extraction techniques which use low amounts of solvents or no solvents are considered ideal alternatives. This paper presents an overview of green extraction procedures and sample preparation methodologies, briefly introduces their theoretical principles, and describes the recent developments in food, pharmaceutical, environmental and bioanalytical chemistry applications.

Headspace volatiles influenced by infusion matrix and their release persistence: a case study of oolong tea

The perceived aroma of oolong tea is primarily and directly affected by its infusion matrix, and the release persistence of headspace volatiles can better illustrate the persistent aroma. Headspace solid phase microextraction coupled with gas chromatography-mass spectrometry was performed to analyze the headspace constituents of oolong tea. The presence of the infusion matrix seemed to prevent the headspace release of certain odorants. The release of indole, nerolidol, and α-farnesene was also remarkably enhanced or depressed (2.70, 1.56, and 0.69-fold in tea infusion versus in dry leaves). Moreover, the amount of volatile species gradually decreased with increased water ratio. Eight odorants were determined to be stable and persistent during continuous infusion, whereas six were determined to be less persistent (gradually decreased or stopped releasing). The volatile dilution test further confirmed the persistent release of nerolidol.

Current Trends in Fully Automated On-Line Analytical Techniques for Beverage Analysis

The determination of target analytes in complex matrices such as beverages requires a series of analytical steps to obtain a reliable analysis. This critical review presents the current trends in sample preparation techniques based on solid phase extraction miniaturization, automation and on-line coupling. Techniques discussed include solid-phase extraction (SPE), solid-phase microextraction (SPME), in-tube solid-phase microextraction (in-tube SPME) and turbulent-flow chromatography (TFC). Advantages and limitations, as well as several of their main applications in beverage samples are discussed. Finally, fully automated on-line systems that involve extraction, chromatographic separation, and tandem mass spectrometry in one-step are introduced and critically reviewed.

Study of the aroma formation and transformation during the manufacturing process of oolong tea by solid-phase micro-extraction and gas chromatography-mass spectrometry combined with chemometrics

Oolong tea is a typical semi-fermented tea and is famous for its unique aroma. The aim of this study was to compare the volatile compounds during manufacturing process to reveal the formation of aroma. In this paper, a method was developed based on head-space solid phase microextraction/gas chromatography-mass spectrometry (HS-SPME/GC-MS) combined with chemometrics to assess volatile profiles during manufacturing process (fresh leaves, sun-withered leaves, rocked leaves and leaves after de-enzyming). A total of 24 aroma compounds showing significant differences during manufacturing process were identified. Subsequently, according to these aroma compounds, principal component analysis and hierarchical cluster analysis showed that the four samples were clearly distinguished from each other, which suggested that the 24 identified volatile compounds can represent the changes of volatile compounds during the four steps. Additionally, sun-withering, rocking and de-enzyming can influence the variations of volatile compounds in different degree, and we found the changes of volatile compounds in withering step were less than other two manufacturing process, indicating that the characteristic volatile compounds of oolong tea might be mainly formed in rocking stage by biological reactions and de-enzyming stage through thermal chemical transformations rather than withering stage. This study suggested that HS-SPME/GC-MS combined with chemometrics methods is accurate, sensitive, fast and ideal for rapid routine analysis of the aroma compounds changes in oolong teas during manufacturing processing.

Implementation of CsLIS/NES in linalool biosynthesis involves transcript splicing regulation in Camellia sinensis

Volatile terpenoids produced in tea plants (Camellia sinensis) are airborne signals interacting against other ecosystem members, but also pleasant odorants of tea products. Transcription regulation (including transcript processing) is pivotal for plant volatile terpenoid production. In this study, a terpene synthase gene CsLIS/NES was recovered from tea plants (C. sinensis cv. "Long-Men Xiang"). CsLIS/NES transcription regulation resulted in 2 splicing forms: CsLIS/NES-1 and CsLIS/NES-2 lacking a 305 bp-fragment at N-terminus, both producing (E)-nerolidol and linalool in vitro. Transgenic tobacco studies and a gene-specific antisense oligo-deoxynucleotide suppression applied in tea leaves indicated that CsLIS/NES-1, localized in chloroplasts, acted as linalool synthase, whereas CsLIS/NES-2 localized in cytosol, functioned as a potential nerolidol synthase, but not linalool synthase. Expression patterns of the 2 transcript isoforms in tea were distinctly different and responded differentially to the application of stress signal molecule methyl jasmonate. Leaf expression of CsLIS/NES-1, but not CsLIS/NES-2, was significantly induced by methyl jasmonate. Our data indicated that distinct transcript splicing regulation patterns, together with subcellular compartmentation of CsLIS/NE-1 and CsLIS/NE-2 implemented the linalool biosynthesis regulation in tea plants in responding to endogenous and exogenous regulatory factors.

A comparative study of volatile components in Dianhong teas from fresh leaves of four tea cultivars by using chromatography-mass spectrometry, multivariate data analysis, and descriptive sensory analysis

Dianhong teas produced from fresh leaves of different tea cultivars (YK is Yunkang No. 10, XY is Xueya 100, CY is Changyebaihao, SS is Shishengmiao), were compared in terms of volatile compounds and descriptive sensory analysis. A total of 73 volatile compounds in 16 tea samples were tentatively identified. YK, XY, CY, and SS contained 55, 53, 49, and 51 volatile compounds, respectively. Partial least squares-discriminant analysis (PLS-DA) and hierarchical cluster analysis (HCA) were used to classify the samples, and 40 key components were selected based on variable importance in the projection. Moreover, 11 flavor attributes, namely, floral, fruity, grass/green, woody, sweet, roasty, caramel, mellow and thick, bitter, astringent, and sweet aftertaste were identified through descriptive sensory analysis (DSA). In generally, innate differences among the tea varieties significantly affected the intensities of most of the key sensory attributes of Dianhong teas possibly because of the different amounts of aroma-active and taste components in Dianhong teas.

Changes in flavor volatile composition of oolong tea after panning during tea processing

Panning is a processing step used in manufacturing of some varieties of oolong tea. There is limited information available on effects of panning on oolong tea flavors. The goal of this study was to determine effects of panning on flavor volatile compositions of oolong using Gas Chromatography-Mass Spectrometry (GC-MS) and Gas Chromatography-Olfactometry (GC-O). SDE and SPME techniques were applied for extraction of volatiles in panned and unpanned teas. A total of 190 volatiles were identified from SDE and SPME extractions using GC-MS and GC-O. There were no significant differences (P > 0.05) in aldehyde or terpene contents of unpanned and panned tea. However, alcohols, ketones, acids and esters contents were significantly reduced by panning. Among 12 major volatiles previously used for identification and quality assessment of oolong tea, trans nerolidol, 2- hexenal, benzaldehyde, indole, gernaiol, and benzenacetaldehyde contents were significantly decreased (P < 0.05) by panning. Panning increased (P < 0.05) contents of linalool oxide, cis jasmone, and methyl salicylate. The GC-O study also showed an increase of aroma active compounds with sweet descriptions and decrease of aroma active compounds with fruity and smoky descriptions after panning. Panning significantly changes the volatile compositions of the tea and created new aroma active compounds. Results from this study can be used in quality assessment of panned oolong tea.

Nerolidol: A Sesquiterpene Alcohol with Multi-Faceted Pharmacological and Biological Activities

Nerolidol (3,7,11-trimethyl-1,6,10-dodecatrien-3-ol) is a naturally occurring sesquiterpene alcohol that is present in various plants with a floral odor. It is synthesized as an intermediate in the production of (3E)-4,8-dimethy-1,3,7-nonatriene (DMNT), a herbivore-induced volatile that protects plants from herbivore damage. Chemically, nerolidol exists in two geometric isomers, a trans and a cis form. The usage of nerolidol is widespread across different industries. It has been widely used in cosmetics (e.g., shampoos and perfumes) and in non-cosmetic products (e.g., detergents and cleansers). In fact, U.S. Food and Drug Administration (FDA) has also permitted the use of nerolidol as a food flavoring agent. The fact that nerolidol is a common ingredient in many products has attracted researchers to explore more medicinal properties of nerolidol that may exert beneficial effect on human health. Therefore, the aim of this review is to compile and consolidate the data on the various pharmacological and biological activities displayed by nerolidol. Furthermore, this review also includes pharmacokinetic and toxicological studies of nerolidol. In summary, the various pharmacological and biological activities demonstrated in this review highlight the prospects of nerolidol as a promising chemical or drug candidate in the field of agriculture and medicine.

SDE and SPME Analysis of Flavor Compounds in Jin Xuan Oolong Tea

Simultaneous distillation-extraction (SDE) and solid phase micro extraction (SPME) are procedures used for the isolation of flavor compounds in foods. The purpose of this study was to optimize SDE conditions (solvent and time) and to compare SDE with SPME for the isolation of flavor compounds in Jin Xuan oolong tea using GC-MS and GC-O. The concentration of volatile compounds isolated with diethyl ether was higher (P < 0.05) than for dichloromethane and concentration was higher at 40 min (P < 0.05) than 20 or 60 min extractions. For SDE, 128 volatiles were identified using GC-MS and 45 aroma active compounds using GC-O. Trans-nerolidol was the most abundant compound in oolong tea. The number of volatiles identified using GC-MS was lower in SPME than SDE. For SPME, 59 volatiles and 41 aroma active compounds were identified. The composition of the volatiles isolated by the 2 methods differed considerably but provided complementary information.

Quantification of nerolidol in mouse plasma using gas chromatography-mass spectrometry

Nerolidol is a naturally occurring sesquiterpene found in the essential oils of many types of flowers and plants. It is frequently used in cosmetics, as a food flavoring agent, and in cleaning products. In addition, nerolidol is used as a skin penetration enhancer for transdermal delivery of therapeutic drugs. However, nerolidol is hemolytic at low concentrations. A simple and fast GC-MS method was developed for preliminary quantification and assessment of biological interferences of nerolidol in mouse plasma after oral dosing. Calibration curves were linear in the concentration range of 0.010-5 μg/mL nerolidol in mouse plasma with correlation coefficients (r) greater than 0.99. Limits of detection and quantification were 0.0017 and 0.0035 μg/mL, respectively. The optimized method was successfully applied to the quantification of nerolidol in mouse plasma.