Determination of Volatile Chemical Constitutes in Tea by Simultaneous Distillation Extraction, Vacuum Hydrodistillation and Thermal Desorption

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

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

Volatile Organic Compounds of Anchote Tuber and Leaf Extracted Using Simultaneous Steam Distillation and Solvent Extraction

Anchote (Coccinia abyssinica (Lam.) (Cogn)) is an endemic and potentially valuable crop of Ethiopia principally categorized under root and tuber crops, and its newly growing leaves along with the tendrils are also used as nutritious vegetable served after being cooked. Leaf and tuber powders were extracted for the first time to identify volatile organic compounds by simultaneous steam distillation and solvent extraction (SDE) and characterized using gas chromatography mass spectrometry (GC-MS). VOCs having an area percentage above 0.5% were used for identification analysis. From the results, thirty volatile flavor compounds from leaves and fifteen from tubers were identified with the total fraction yield of 770.57 mg/kg and 4536.91 mg/kg, respectively, and from the 30 compounds identified from leaf 16 were distinguished in each of the tested accessions. Ethyl acetate 90.47% (697.13 mg/kg) was detected in a higher amount exhibiting >1% peak area. The rest 6.03% (46.46 mg/kg) were minor quantities (<1%) of the total (770.57 mg/kg) volatile flavor fraction. Among the 15 identified compounds in the tuber, ethyl acetate was the only major compound that accounted together for 99.15% (4498.33 mg/kg) of the total volatile flavor fraction and 0.85% (38.58 mg/kg) being reported in minor quantities (<1%). The SDE extraction and GC-MS analysis of anchote leaves and tubers successfully identified various volatile flavor compounds, which indicates that anchote was found to be a potential source of volatile flavor compounds that can be used as a food flavoring agent and in folk medicines. Thus, this study confirms that anchote leaf and tuber can be used for more specific and valuable applications in food and medicine industries.

Effects of Different Extraction Methods on Vanilla Aroma

To establish the analytic conditions for examining the aroma quality of vanilla pods, we compared different extraction methods and identified a suitable option. We utilized headspace solid-phase microextraction (HS-SPME), steam distillation (SD), simultaneous steam distillation (SDE) and alcoholic extraction combined with gas chromatography (GC) and gas chromatography–mass spectrometry (GC-MS) to identify volatile components of vanilla pods. A total of 84 volatile compounds were identified in this experiment, of which SDE could identify the most volatile compounds, with a total of 51 species, followed by HS-SPME, with a total of 28 species. Ten volatile compounds were identified by extraction with a minimum of 35% alcohol. HS-SPME extraction provided the highest total aroma peak areas, and the peak areas of aldehydes, furans, alcohols, monoterpenes and phenols compounds were several times higher than those of the other extraction methods. The results showed that the two technologies, SDE and HS-SPME, could be used together to facilitate analysis of vanilla pod aroma.

Chemical Profile and Phytotoxic Action of Hibiscus trionum Essential Oil

The chemical profile and phytotoxic action of Hibiscus trionum essential oil (EO) was studied. In total 17 compounds were identified via GC/MS, representing 94.18 % of the entire oil, with phytol (40.37 %) being the dominant constituent. Bioassay revealed that the EO inhibited root elongation of Medicago sativa and Amaranthus retroflexus by 32.66 % and 61.86 % at 5 mg/mL, respectively; meanwhile, the major component phytol also exhibited significant phytotoxic activity, suppressing radical elongation of Pennisetum alopecuroides, M. sativa and A. retroflexus by 26.08 %, 27.55 % and 43.96 % at 1 mg/mL, respectively. The fact that the EO showed weaker activity than phytol implied that some constituents might trigger antagonistic action to decrease the oil's activity. Our study is the first on the chemical profile and phytotoxic effect of H. trionum EO.

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

To investigate the key aroma compounds in Laoshan green teas (Huangshan (S1), Changling (S2), and Fangling (S3)), gas chromatography-mass spectrometry-olfactometry (GC-MS-O), a flame photometric detector (FPD), odor activity value (OAV), and comprehensive two-dimensional gas chromatography mass spectrometry (GC × GC-qMS) were employed. A total of 50 aroma compounds were perceived and 24 compounds were identified as important compounds related to OAV, such as dimethyl sulfide (OAV: 126-146), skatole (OAV: 27-50), furaneol (OAV: 8-27), (Z)-jasmone (OAV: 16-23), 2-methylbutanal (OAV: 15-22), and 3-methylbutanal (OAV: 68-87). Furthermore, the S-curve method was used to research the effect of aroma compounds on the threshold of aroma recombination (AR). The AR thresholds decreased from 3.8 mL to 0.45, 0.66, 0.93, 0.95, 0.75, 1.09, 3.01, and 2.57 mL after addition of eight compounds (skatole, furaneol, (Z)-jasmone, α-damascenone, sclareololide, dihydroactinidiolide, vanillin, and δ-valerolactone), indicating that those compounds (OAV >1) were contributors to the overall aroma of Laoshan teas.

Comparison of volatile profiles and bioactive components of sun-dried Pu-erh tea leaves from ancient tea plants on Bulang Mountain measured by GC-MS and HPLC

To explore the volatile profiles and the contents of ten bioactive components (polyphenols and caffeine) of sun-dried Pu-erh tea leaves from ancient tea plants on Bulang Mountain, 17 samples of three tea varieties were analyzed by headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and high-performance liquid chromatography (HPLC). A total of 75 volatile components were tentatively identified. Laomaner (LME), Laobanzhang (LBZ), and other teas on Bulang Mountain (BL) contained 70, 53, and 71 volatile compounds, respectively. Among the volatile compounds, alcohols (30.2%-45.8%), hydrocarbons (13.7%-17.5%), and ketones (12.4%-23.4%) were qualitatively the most dominant volatile compounds in the different tea varieties. The average content of polyphenol was highest in LME (102.1 mg/g), followed by BL (98.7 mg/g) and LBZ (88.0 mg/g), while caffeine showed the opposite trend, 27.3 mg/g in LME, 33.5 mg/g in BL, and 38.1 mg/g in LBZ. Principal component analysis applied to both the volatile compounds and ten bioactive components showed a poor separation of samples according to varieties, while partial least squares-discriminant analysis (PLS-DA) showed satisfactory discrimination. Thirty-four volatile components and five bioactive compounds were selected as major discriminators (variable importance in projection (VIP) >1) among the tea varieties. These results suggest that chromatographic data combined with multivariate analysis could provide a useful technique to characterize and distinguish the sun-dried Pu-erh tea leaves from ancient tea varieties on Bulang Mountain.

Characterization of the key aroma compounds in Longjing tea using stir bar sorptive extraction (SBSE) combined with gas chromatography-mass spectrometry (GC-MS), gas chromatography-olfactometry (GC-O), odor activity value (OAV), and aroma recombination

Longjing tea is the most famous premium green tea, and is regarded as the national tea in China, with its attractive aroma contributing as a prime factor for its general acceptability; however, its key aroma compounds are essentially unknown. In the present study, volatile compounds from Longjing tea were extracted and examined using stir bar sorptive extraction (SBSE) combined with gas chromatography-mass spectrometry (GC-MS). Data obtained from the present study revealed that 151 volatile compounds from 16 different chemical classes were identified by GC-MS analysis. Enols (8096 µg/kg), alkanes (6744 µg/kg), aldehydes (6442 µg/kg), and esters (6161 µg/kg) were the four major chemical classes and accounted for 54% of the total content of volatile compounds. Geraniol (6736 µg/kg) was the most abundant volatile compound in Longjing tea, followed by hexanal (1876 µg/kg) and β-ionone (1837 µg/kg). Moreover, 14 volatile compounds were distinguished as the key aroma compounds of Longjing tea based on gas chromatography-olfactometry (GC-O) analysis, odor activity value (OAV) calculations, and a preliminary aroma recombination experiment, including 2-methyl butyraldehyde, dimethyl sulfoxide, heptanal, benzaldehyde, 1-octen-3-ol, (E, E)-2,4-heptadienal, benzeneacetaldehyde, linalool oxide I, (E, E)-3,5-octadien-2-one, linalool, nonanal, methyl salicylate, geraniol, and β-ionone. This is the first comprehensive report describing the aroma characterizations and the key aroma compounds in Longjing tea using SBSE/GC-MS. The findings from this study contribute to the scientific elucidation of the chemical basis for the aromatic qualities of Longjing tea.

Comparison and Identification of the Aroma-Active Compounds in the Root of Angelica dahurica

Solid-phase microextraction (SPME), purge and trap (P&T), stir bar sportive extraction (SBSE), and dynamic headspace sampling (DHS) were applied to extract, separate and analyze the volatile compounds in the roots of Hangbaizhi, Qibaizhi, and Bobaizhi and the GC-O-MS/MS (AEDA) was utilized for the quantification of key aroma compounds. Totals of 52, 54, and 43 aroma-active compounds extracted from the three samples by the four extraction methods were identified. Among these methods, the SPME effectively extracted the aroma compounds from the A. dahurica. Thus, using the SPME methods for quantitative analysis based on external standards and subsequent dilution analyses, totals of 20, 21, and 17 aroma compounds were detected in the three samples by the sniffing test, and sensory evaluations indicated that the aromas of A. dahurica included herb, spice, and woody. Finally, principal component analysis (PCA) showed that the three kinds A. dahurica formed three separate groups, and partial least squares discriminant analysis (PLS-DA) showed that caryophyllene, (-)-β-elemene, nonanal, and β-pinene played an important role in the classification of A. dahurica.

Functional Characterization of Salicylic Acid Carboxyl Methyltransferase from Camellia sinensis, Providing the Aroma Compound of Methyl Salicylate during the Withering Process of White Tea

Methyl salicylate (MeSA) is one of the volatile organic compounds (VOCs) that releases floral scent and plays an important role in the sweet flowery aroma of tea. During the withering process for white tea producing, MeSA was generated by salicylic acid carboxyl methyltransferase (SAMT) with salicylic acid (SA), and the specific floral scent was formed. In this study, we first cloned a CsSAMT from tea leaves (GenBank accession no. MG459470) and used Escherichia coli and Saccharomyces cerevisiae to express the recombinant CsSAMT. The enzyme activity in prokaryotic and eukaryotic expression systems was identified, and the protein purification, substrate specificity, pH, and temperature optima were investigated. It was shown that CsSAMT located in the chloroplast, and the gene expression profiles were quite different in tea organs. The obtained results might give a new understanding for tea aroma formation, optimization, and regulation and have great significance for improving the specific quality of white tea.

Direct Contact Sorptive Extraction: A Robust Method for Sampling Plant Volatiles in the Field

Plants produce volatile organic compounds (VOCs) with diverse structures and functions, which change in response to environmental stimuli and have important consequences for interactions with other organisms. To understand these changes, in situ sampling is necessary. In contrast to dynamic headspace (DHS), which is the most often employed method, direct contact sampling employing a magnetic stir bar held in place by a magnet eliminates artifacts produced by enclosing plant materials in glass or plastic chambers. Direct-contact sorptive extraction (DCSE) using polydimethylsiloxane coated stir bars (Twisters) coated stir bars is more sensitive than DHS, captures a wider range of compounds, minimizes VOC collection from neighboring plants, and distinguishes the effects of herbivory in controlled and field conditions. Because DCSE is relatively inexpensive and simple to employ, scalability of field trials can be expanded concomitant with increased sample replication. The sensitivity of DCSE combined with the spectral deconvolution data analysis software makes the two ideal for comprehensive, in situ profiling of plant volatiles.

Extraction and preparation of high-aroma and low-caffeine instant green teas by the novel column chromatographic extraction method with gradient elution

The lack of aroma and natural taste is a critical problem in production and consumption of instant green teas. A method to prepare instant green teas high in-natural-aroma and low-caffeine by the novel column chromatographic extraction with gradient elution is reported. This method simultaneously extracted aroma (or volatile) and non-aroma compounds from green tea. Green tea was loaded into columns with 2.0-fold of petroleum ether (PE): ethanol (8:2). After standing for 3 h until the aroma compounds dissolved, the column was sequentially eluted with 3.0-fold 40% ethanol and 3.5-fold water. The eluant was collected together and automatically separated into PE and ethanol aqueous phases. The aroma extracts was obtained by vacuum-evaporation of PE phase at 45 °C. The ethanol aqueous phase was vacuum-concentrated to aqueous and partially or fully decaffeinated with 4% or 9% charcoal at 70 °C. A regular instant green tea with epigallocatechin-3-gallate: caffeine of 3.5:1 and a low-caffeine instant green tea (less than 1% caffeine) with excellent aroma and taste were prepared, by combining the aroma and non-aroma extracts at a 1:10 ratio. This work provides a practical approach to solve the low-aroma and low-taste problems in the production of high quality instant green teas.

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.

Optimizing targeted/untargeted metabolomics by automating gas chromatography/mass spectrometry workflows

New database building and MS subtraction algorithms have been developed for automated, sequential two-dimensional gas chromatography/mass spectrometry (GC-GC/MS). This paper reports the first use of a database building tool, with full mass spectrum subtraction, that does not rely on high resolution MS data. The software was used to automatically inspect GC-GC/MS data of high elevation tea from Yunnan, China, to build a database of 350 target compounds. The database was then used with spectral deconvolution to identify 285 compounds by GC/MS of the same tea. Targeted analysis of low elevation tea by GC/MS resulted in the detection of 275 compounds. Non-targeted analysis, using MS subtraction, yielded an additional eight metabolites, unique to low elevation tea.

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.

Effect of aging on volatile compounds in cooked beef

Volatiles in the headspace of beef cooked at 180 °C were analyzed using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS), and the effects of aging were evaluated. Seventy volatile substances including non-aromatic, homocyclic, and heterocyclic compounds were identified. A significant positive regression model for storage could be adopted for toluene, benzeneacetaldehyde, 2-formylfuran, pyrazine, 2,6-dimethylpyrazine, 2,3-dimethylpyrazine, 2-acetylthiazole, and 2-formyl-3-methylthiophene. Increases in the quantity of these compounds, with the exception of toluene, suggest the importance of the Strecker and Maillard reactions in cooked meat previously aged under vacuum conditions. As such, the aging process may lead to an increase not only in the amount of compounds related to the taste of meat, but also in the quantity of odor-active compounds. The increased quantity of toluene during storage seemed to be influenced by lipid oxidation.

Metabolite profiling of Camellia sinensis by automated sequential, multidimensional gas chromatography/mass spectrometry reveals strong monsoon effects on tea constituents

Seasonal variation in tea (Camellia sinensis (L.) Kuntze; Theaceae) chemistry was investigated using automated sequential, multidimensional gas chromatography/mass spectrometry (GC-GC/MS). Metabolite libraries were produced for teas harvested from the Bulang Mountains in Yunnan, China before and after the onset of the East Asian Monsoon. A total of 201 spring and 196 monsoon metabolites were identified, with 169 common and 59 seasonally unique compounds. An additional 163 metabolites were detected but their identity could not be confirmed. Spectral deconvolution of GC/MS data was used to measure the relative concentrations in the teas. Within each family individual metabolite concentrations increased, decreased and stayed the same. The major constituents in both teas were linalool (28%), geraniol (13%), α-terpineol (10%), hotrienol (4%) and nerol (3%). This work provides the foundation to monitor seasonal variations of tea chemistry.

Volatile aroma compounds in various brewed green teas

This study identifies and semi-quantifies aroma volatiles in brewed green tea samples. The objectives of this study were to identify using a gas chromatograph-mass spectrometer (GC-MS) paired with a headspace solid-phase micro-extraction (HS-SPME) the common volatile compounds that may be responsible for aroma/flavor of the brewed liquor of a range of green tea samples from various countries as consumed and to determine if green teas from the same region have similarities in volatile composition when green tea samples are prepared for consumption. Twenty-four green tea samples from eight different countries were brewed as recommended for consumer brewing. The aroma volatiles were extracted by HS-SPME, separated on a gas chromatograph and identified using a mass spectrometer. Thirty-eight compounds were identified and the concentrations were semi-quantified. The concentrations were lower than those reported by other researchers, probably because this research examined headspace volatiles from brewed tea rather than solvent extraction of leaves. No relationship to country of origin was found, which indicates that other factors have a greater influence than country of origin on aroma.

Volatile profile analysis and quality prediction of Longjing tea (Camellia sinensis) by HS-SPME/GC-MS

This study aimed to analyze the volatile chemical profile of Longjing tea, and further develop a prediction model for aroma quality of Longjing tea based on potent odorants. A total of 21 Longjing samples were analyzed by headspace solid phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). Pearson's linear correlation analysis and partial least square (PLS) regression were applied to investigate the relationship between sensory aroma scores and the volatile compounds. Results showed that 60 volatile compounds could be commonly detected in this famous green tea. Terpenes and esters were two major groups characterized, representing 33.89% and 15.53% of the total peak area respectively. Ten compounds were determined to contribute significantly to the perceived aroma quality of Longjing tea, especially linalool (0.701), nonanal (0.738), (Z)-3-hexenyl hexanoate (-0.785), and β-ionone (-0.763). On the basis of these 10 compounds, a model (correlation coefficient of 89.4% and cross-validated correlation coefficient of 80.4%) was constructed to predict the aroma quality of Longjing tea. Summarily, this study has provided a novel option for quality prediction of green tea based on HS-SPME/GC-MS technique.

Optimization of headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry for detecting methoxyphenolic compounds in pu-erh tea

A method based on headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry was developed for the analysis of volatile methoxyphenolic compounds in pu-erh tea. Six fibers with different polarities were initially evaluated. The 75 μm carboxen/polydimethylsiloxane fiber exhibited the highest extraction efficiency and was selected for further optimization. A Plackett-Burman design was used to screen for the brewing proportion of tea and water, amount of pu-erh tea, ionic strength, extraction time, extraction temperature, desorption time, rate of agitation, and equilibrium time. A Box-Behnken design was then applied to optimize the significant factors. Under optimal conditions, the proposed method affords a wide range of linearity, high linear regression coefficients (0.996-0.999), less than 9.0% repeatability of relative standard deviation, and limits of detection ranging from 2.31 to 21.80 ng/g. The proposed method has satisfactory accuracy, with recoveries of 79.08-113.9%. This method was successfully applied for the analysis of pu-erh tea samples.

Simultaneous Distillation Extraction of Some Volatile Flavor Components from Pu-erh Tea Samples-Comparison with Steam Distillation-Liquid/Liquid Extraction and Soxhlet Extraction

A simutaneous distillation extraction (SDE) combined GC method was constructed for determination of volatile flavor components in Pu-erh tea samples. Dichloromethane and ethyl decylate was employed as organic phase in SDE and internal standard in determination, respectively. Weakly polar DB-5 column was used to separate the volatile flavor components in GC, 10 of the components were quantitatively analyzed, and further confirmed by GC-MS. The recovery covered from 66.4%–109%, and repeatability expressed as RSD was in range of 1.44%–12.6%. SDE was most suitable for the extraction of the anlytes by comparing with steam distillation-liquid/liquid extraction and Soxhlet extraction. Commercially available Pu-erh tea samples, including Pu-erh raw tea and ripe tea, were analyzed by the constructed method. the high-volatile components, such as benzyl alcohol, linalool oxide, and linalool, were greatly rich in Pu-erh raw teas, while the contents of 1,2,3-Trimethoxylbenzene and 1,2,4-Trimethoxylbenzene were much high in Pu-erh ripe teas.