Flavor characteristics of lapsang souchong and smoked lapsang souchong, a special Chinese black tea with pine smoking process

Insight into aroma dynamic changes during the whole manufacturing process of smoked Lapsang Souchong tea

Smoked Lapsang Souchong tea (SLST) is a distinctive black tea known for its smokey, fruity, and pine flavor. This study analyzed the aroma dynamic changes during the whole manufacturing process of SLST utilizing E-nose, HS-SPME-GC-MS, and HS-SPME-GC-O-MS. Fresh tea leaves primarily contain green and floral volatiles, such as (E)-2-hexenal (OAV 33.41) and linalool (OAV 313.88). Withering and drying processes introduce pinewood smoke-derived phenolic and terpenoid compounds, such as guaiacols (OAV 77.05) and α-terpineol (OAV 1.08), crucial for the tea's smoky and woody aroma. The study further highlights glycoside hydrolysis and lipid oxidation pathways in generating key tea-derived volatiles during fermentation, contributing to the fruity and floral notes in SLST. Pinewood smoke was identified as a major source of smoky volatiles, with longifolene and α-terpineol being unique to pinewood. These findings elucidate the formation pathways of the key volatile compounds and the impact of traditional processing on SLST's aroma profile.

Identifying the structures and taste characteristics of two novel Maillard reaction products in tea

Maillard reaction products (MRPs) produced during thermal processing of tea are intimately related to its flavor. Our recent work revealed that both levels of l-theanine and d-galacturonic acid in tea leaves decreased dramatically during drying, whereas the specific MRPs from l-theanine and d-galacturonic acid remain elusive. Here, the MRPs formed from l-theanine and d-galacturonic acid were investigated and their taste characteristics and the involved mechanisms were explored. Two novel MRPs from l-theanine and d-galacturonic acid were identified as 1-(1-carboxy-4-(ethylamino)-4-oxobutyl)-3-hydroxypyridin-1-ium (MRP 1) and 2-(2-formyl-1H-pyrrole-1-yl) theanine (MRP 2). MRP 1 and MRP 2 accumulated in dark tea and black tea and were associated with sour (threshold, 0.25 mg/mL) and astringent tastes and an umami taste (threshold, 0.18 mg/mL), respectively. Molecular docking revealed that the taste characteristics of MRPs may be due to strong binding to umami taste receptor proteins (CASR, T1R1/T1R3) and the sour taste protein OTOP1 via hydrogen bonds and hydrophobic interactions.

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.

Aroma Identification and Classification in 18 Kinds of Teas (Camellia sinensis) by Sensory Evaluation, HS-SPME-GC-IMS/GC × GC-MS, and Chemometrics

Tea (Camellia sinensis) is one of the most popular beverages worldwide. Many types of tea products continuously emerge in an endless stream; so, the classification of tea becomes more difficult. Aroma is a vital indicator of tea quality. The present study deals with the identification of aroma compounds in 18 different kinds of tea belonging to three typical tea varieties, including green tea, oolong tea, and black tea, using GC-IMS and GC × GC-O-MS. Moreover, the clustering of all 18 tea samples and the in depth correlation analysis between sensory evaluation and instrumental data were performed using the PCA and OPLS-DA. The results revealed that in all 18 kinds of tea, a total of 85 aroma compounds were detected by GC-IMS, whereas 318 were detected by GC × GC-O-MS. The PCA result revealed that green tea, oolong tea, and black tea could be clearly separated based on their peak areas. The OPLS-DA result showed that a total of 49 aroma compounds with VIP value > 1.0 could be considered as the potential indicators to quickly classify or verify tea types. This study not only compared the aroma differences across different types of teas, but also provided ideas for the rapid monitoring of tea quality and variety.

Analysis of Volatile and Nonvolatile Constituents in Gin by Direct-Infusion Ultrahigh-Resolution ESI/APPI FT-ICR Mass Spectrometry

Gin is one of the most consumed distilled alcoholic spirits worldwide, with more than 400 million liters sold every year. It is most often produced through redistillation of agricultural ethanol in the presence of botanicals, most notably juniper berries, which give gin its characteristic flavor. Due to its natural ingredients, gin is a complex mixture of hundreds of volatile and nonvolatile chemical constituents. In this work, ultrahigh-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry was used for the compositional analysis of 16 commercially produced gins. Two complementary ionization methods, namely, electrospray ionization (ESI) and atmospheric-pressure photoionization (APPI), were employed to cover a wider compositional space. Each gin provided unique chemical fingerprints by ESI and APPI, which allowed semiquantitative analysis of 135 tentatively identified compounds, including terpene hydrocarbons, terpenoids, phenolics, fatty acids, aldehydes, and esters. Most of these compounds have not been previously reported in gins. While chemical fingerprints were rather similar between most products, some products contained unique compounds due to their special natural ingredients or the production methods applied. For instance, a barrel-matured gin contained a high content of syringaldehyde and sinapaldehyde, which are typical phenolic aldehydes originated from oak wood. In addition, the relative abundance of vanillin, vanillic acid, gallic acid, coniferyl aldehyde, and syringaldehyde was clearly higher than in the other gin samples. Ultrahigh-resolution FT-ICR MS serves as a powerful tool for direct chemical fingerprinting of gin or any other distilled spirit, which can be used for rapid product quality screening, product optimization, or possible counterfeit product discovery.

Effects of different woods in barbecuing: Consumers' sensory perception and liking of grilled chicken meat

The sensory effects of grilling wood on consumers' response are poorly understood, despite their potentiality in diversifying dishes. This study investigated both the effects of six materials (beech tree wood, Turkey oak wood, Sangiovese grapevine wood, olive wood, strawberry tree wood, charcoal briquettes) used to grill chicken breast meat on liking and sensory perception and consumers' interest in using wood for grilling. A consumer test was conducted (n = 99 subjects, 45% males, aged from 18 to 65 years), applying a Rate-All-That-Apply test, a liking test, and a questionnaire exploring the interest, the perceived value and the sustainability of wood as part of the food processing. The type of wood clearly affected the consumers' sensory perception and acceptability of meat. Strawberry tree wood was the most connoted and divisive sample. Turkey oak, olive tree and Sangiovese grapevine woods were associated to milder sensory profile. Two clusters were found (respectively with 54% participants in Cl1 and 46% in Cl2), with opposite preferences: while Cl2 preferred meat grilled with the most connotating wood (Strawberry tree wood) characterized by bitterness while Cl1 on the opposite preferred meat grilled with the milder woods. Consumers showed a high interest for grilling material, wood origin and wood botanical species, independently from the cluster. Strawberry tree wood was the material that most strongly connotated grilled meat and thus the most divisive one in terms of liking. Different varieties of wood and certified sustainable wood can valorize the grilling process in food services.

Characterization of the key aroma-active compounds in high-grade Dianhong tea using GC-MS and GC-O combined with sensory-directed flavor analysis

Dianhong tea (DHT) is popular for its pleasant caramel-like aroma. In this study, the aroma profile of high-grade DHT have been studied using gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O) combined with headspace solid phase microextraction (HS-SPME). A total of 52 aroma-active compounds were identified by GC-O coupled with aroma extract dilution analysis (AEDA) and odor specific magnitude estimation (Osme). Among them, quantification of 21 aroma-active compounds indicated that the content of linalool (5928 µg/kg) was the highest in high-grade DHT, followed by phenylethanol (3923 µg/kg) and phenylacetaldehyde (1801 µg/kg). Sensory-directed aroma recombination and omission tests further verified that phenylacetaldehyde, linalool, geraniol and 3-ethyl-2,5-dimethylpyrazine were important contributors to the overall sensory characteristics of high-grade DHT which dominated mainly by floral, sweet and caramel-like odors. This work will provide a theoretical reference for comprehensively understanding the aroma characteristic of DHT.

Effects of microbial diversity and phospholipids on flavor profile of caviar from hybrid sturgeon (Huso dauricus × Acipenser schrencki)

Thirty-seven volatiles were identified by gas chromatography-ion mobility spectrometry in sturgeon caviar. Alkenes (37, 43), alcohols (30, 36), aldehydes (9, 10), and esters (11, 13) were detected by two-dimensional gas chromatography-time-off-flight mass spectrometry in fresh and stored caviar, respectively. Alkenes (humulene, caryophyllene, longifolene, and d-limonene), aldehydes (heptanal, hexanal, pentanal, and 3-methyl butanal), and 2-ethyl-1-hexanol were sniffed and described as providing fresh, fatty, and fishy attributes by gas chromatography-olfactometry. The fungal genera of Apiotrichum, Penicillium, Filobasidium, Gibberella, and Cladosporium and 16 bacterial genera were significantly correlated with variations in the contents of 25 aldehydes and 11 ketones. Nine strains, 20 fatty acids, and 69 differential phospholipids were isolated and profiled. Glycerophosphoethanolamine (20:2/20:4), glycerophosphoethanolamine (22:6/22:5), and glycerophosphocholine (16:0/13:0) were significantly associated with the formation of odorants and the proposed mechanism of flavor formation from phospholipids is summarized. This study represents a foundation for achieving targeted preservation and flavor control of caviar.

Functional analysis of the dihydroflavonol 4-reductase family of Camellia sinensis: exploiting key amino acids to reconstruct reduction activity

Anthocyanins and proanthocyanidins (PAs) are important types of flavonoids, plant secondary metabolites with a wide range of industrial and pharmaceutical applications. DFR (dihydroflavonol 4-reductase) is a pivotal enzyme that plays an important role in the flavonoid pathway. Here, four CsDFR genes were isolated from Camellia sinensis, and their overexpression was analyzed in vitro and in vivo. Based on transcription and metabolic analyses, CsDFR expression was closely consistent with catechins and PAs accumulation. Moreover, enzyme activity analyses revealed that the two recombinant proteins CsDFRa and CsDFRc exhibited DFR activity, converting dihydroflavonols into leucoanthocyanins in vitro, but CsDFRb1 and CsDFRb3 did not. CsDFRa and CsDFRc overexpression in AtDFR mutants (tt3) revealed that CsDFRs are involved in the biosynthesis of anthocyanins and PAs, as CsDFRa and CsDFRc restored not only the purple petiole phenotype but also the seed coat color. Site-directed mutagenesis revealed that the two amino acid residues S117 and T123 of CsDFRa play a prominent role in controlling DFR reductase activity. Enzymatic assays indicated that CsDFRa and CsDFRc exhibited a higher affinity for DHQ and DHK, respectively, whereas CsDFRb1^N120S and CsDFRb1^C126T exhibited a higher affinity for DHM. Our findings comprehensively characterize the DFRs from C. sinensis and shed light on their critical role in metabolic engineering.

Black Tea Reduces Diet-Induced Obesity in Mice via Modulation of Gut Microbiota and Gene Expression in Host Tissues

Black tea was reported to alter the microbiome populations and metabolites in diet-induced obese mice and displays properties that prevent obesity, but the underlying mechanism of the preventative effect of black tea on high-fat diet (HFD) induced obesity has not been elucidated. Epigenetic studies are a useful tool for determining the relationship between obesity and environment. Here, we show that the water extract of black tea (Lapsang souchong, LS) reverses HFD-induced gut dysbiosis, alters the tissue gene expression, changes the level of a major epigenetic modification (DNA methylation), and prevents obesity in HFD feeding mice. The anti-obesity properties of black tea are due to alkaloids, which are the principal active components. Our data indicate that the anti-obesity benefits of black tea are transmitted via fecal transplantation, and the change of tissue gene expression and the preventative effects on HFD-induced obesity in mice of black tea are dependent on the gut microbiota. We further show that black tea could regulate the DNA methylation of imprinted genes in the spermatozoa of high-fat diet mice. Our results show a mechanistic link between black tea, changes in the gut microbiota, epigenetic processes, and tissue gene expression in the modulation of diet-induced metabolic dysfunction.

Effects of Different Pre-drying and Drying Methods on Volatile Compounds in the Pericarp and Kernel of Amomum tsao-ko

The effects of twelve different pre-drying and drying methods on the chemical composition in the pericarp and kernel of Amomum tsao-ko were studied. The volatile components were isolated from the samples by simultaneous distillation and extraction and analyzed by gas chromatography-mass spectrometry (GC-MS). Sixty and thirty-eight compounds were identified from pericarp and kernel, respectively, and the main constituents were oxygenated monoterpenes. These compounds were not only significantly affected by pre-drying and drying methods but also varied in content due to different tissue locations. The total volatile content of pericarp varied from 0.70 to 1.55%, with the highest obtained by microwave-dried samples (150 W) and the lowest in freeze-dried samples. The total volatile content of the kernel varied from 6.11 to 10.69%, with the highest content obtained during sun drying (SD) and the lowest content in samples treated with boiling water for 2 min. Oxygenated monoterpenes were the highest compounds in pericarp and kernel, which were also the most affected by drying methods. The highest content of oxygenated monoterpenes in the pericarp (0.77%) could be obtained by boiling water treatment for 5 min, and the highest content of oxygenated monoterpenes in the kernel (7.48%) could be obtained by SD. Additionally, the main components such as 1,8-cineole, 2-carene, (Z)-citral, nerolidol, (Z)-2-decenal, (E)-2-dodecenal, citral, (E)-2-octenal, 4-propylbenzaldehyde, and phthalan showed remarkable variations in pre-drying and drying methods.

Volatile Components and Preliminary Antibacterial Activity of Tamarillo (Solanum betaceum Cav.)

Tamarillo is a nutrient-dense fruit with a unique aroma from its volatile compounds (VCs). In this study, we aimed to compare the volatile profiles: (i) of fresh and freeze-dried tamarillo; (ii) detected using Thermal Desorption–Gas Chromatography–Mass Spectrometry (TD–GC–MS) and Solid-Phase MicroExtraction–Gas Chromatography-Mass Spectrometry (SPME–GC–MS); (iii) of freeze-dried pulp and peel of New Zealand grown tamarillo. The possible antibacterial activity of freeze-dried tamarillo extracts was also investigated. We show that freeze-drying maintained most of the VCs, with some being more concentrated with the loss of water. The most abundant VC in both fresh and freeze-dried tamarillo was hexanoic acid methyl ester for pulp (30% and 37%, respectively), and (E)-3-Hexen-1-ol for peel (36% and 29%, respectively). With the use of TD–GC–MS, 82 VCs were detected for the first time, when compared to SPME–GC–MS. Methional was the main contributor to the overall aroma in both peel (15.4 ± 4.2 μg/g DW) and pulp (118 ± 8.1 μg/g DW). Compared to water as the control, tamarillo extracts prepared by water and methanol extraction showed significant antibacterial activity against E. coli, P. aeruginosa, and S. aureus with zone of inhibition of at least 13.5 mm. These results suggest that freeze-dried tamarillo has a potential for use as a natural preservative to enhance aroma and shelf life of food products.

Effect of different types of smoking materials on the flavor, heterocyclic aromatic amines, and sensory property of smoked chicken drumsticks

This study investigated the effect of different types of smoking materials on the flavor, heterocyclic aromatic amine (HAA) content, and sensory attributes of smoked chicken drumsticks. All smoked samples showed lower pH and L*-value and higher a*-value and b*-value than the control sample (P < 0.05), but no significant differences in water content and water activity (P > 0.05). The samples smoked with sucrose combined with pear-tree woodchips (SP) or green tea leaves (ST) had higher overall acceptability than other samples (P < 0.05). Smoking increased the total HAA content, and the ST sample exhibited the highest total HAA content (P < 0.05). A total of 54 volatile compounds was identified. Overall, SP and ST are suitable for smoked chicken considering the sensory properties, while S and SA are proper for smoked chicken considering the minimization of HAAs, which may provide a theory basis for the production of smoked chicken.

Evaluation of flavor characteristics of bacon smoked with different woodchips by HS-SPME-GC-MS combined with an electronic tongue and electronic nose

This study investigated the effects of different woodchip types (beech, oak, pear, and apple) on the volatile compounds and sensory characteristics of smoked bacon. The volatile compounds were influenced by woodchip types and the total content of ketones and phenols in pear-smoked bacon were higher than in bacon smoked with other woodchips (P < 0.05). The E-tongue combined with E-nose can effectively distinguish the difference in the flavor of bacon smoked with different woodchip types by the signal intensities. Sensory analysis showed that smoking increased bacon's redness, saltiness, and smoky flavor compared with the control (unsmoked bacon) (P < 0.05) and it had little impact on off-odor (P > 0.05). Correlation analysis showed that the E-nose and E-tongue data were highly correlated with contents of alcohols, aldehydes, and ketones. This study revealed that the different smoked materials greatly influenced the flavor and sensory properties of bacon.

Fleeting Beauty-The World of Plant Fragrances and Their Application

This article is devoted to some aspects of the fragrant substances of plant origin applied in the food industry and perfumery as well. Since antiquity many extractive techniques have been developed to obtain essential oils. Some of them are still applied, but new ones, like microwave or ultrasound-assisted extractions, are more and more popular and they save time and cost. Independently of the procedure, the resulting essential oils are the source of many so-called isolates. These can be applied as food additives, medicines, or can be used as starting materials for organic synthesis. Some substances exist in very small amounts in plant material so the extraction is not economically profitable but, after their chemical structures were established and synthetic procedures were developed, in some cases they are prepared on an industrial scale. The substances described below are only a small fraction of the 2000–3000 fragrant molecules used to make our life more enjoyable, either in food or perfumes. Additionally, a few examples of allelopathic fragrant compounds, present in their natural state, will be denoted and some of their biocidal features will be mentioned as an arising “green” knowledge in agriculture.

Peptidoglycans modulating the interaction of a bactericide compound with lipids at the air-water interface

A known monoterpene, named γ-terpineol, was incorporated in mixed Langmuir monolayers composed of dipalmitoyl-phosphoethanolamine (DPPE) and peptidoglycans as a model of microbial membranes. Surface pressure and surface potential isotherms, dynamical surface rheology, Brewster angle microscopy (BAM), and infrared spectroscopy were employed to characterize the compound-membrane interactions. The compound expanded the monolayers denoting repulsive interactions. At 30 mN/m, the monolayer presented lower viscoelastic and in-plane elasticity parameters and an increased all-trans/gauche conformers ratio for the alkyl chains, confirming molecular order. The morphology of the monolayer was analyzed by BAM, which revealed a heterogeneous distribution of γ-terpineol along the mixed monolayer, which tends to segregate. In conclusion, the compound changes the thermodynamic, electric, rheological, morphological, and structural properties of the peptidoglycan-DPPE monolayer, which may be essential to understand, at the molecular level, the action of bioactives in selected membrane models.

The essential oil of Lactuca longidentata Moris and its antioxidant and antimicrobial activities

Lactuca longidentata Moris (Asteraceae) is an endemic species growing only on Mesozoic limestone of central Sardinia. In the present study, the essential oil of the epigeal part of the plant was analyzed by gas chromatography-mass spectrometry (GC/MS). The main volatile components were α-terpineol (27.64%) and limonene (25.8%). The essential oils showed a noteworthy ability of scavenging free radical species (1,1-diphenyl-2-picrylhydrazyl (DPPH) test systems) with a mean half maximal inhibitory concentration IC₅₀ of 32.24 μg/mL. More significant was the inhibition of lipid oxidation that corresponded to an activity 1.5 times lower than that of 2,6-bis(1,1-dimethylethyl)-4-methylphenol (BHT). The essential oil was also assayed on Staphylococcus aureus, Bacillus subtilis, Enterococcus faecalis, Escherichia coli, and Candida albicans by the microdilution broth method and was particularly active against B. subtilis, with a minimal inhibitory concentration (MIC) value of 100 μg/mL.

Assessment of Volatiles and Polyphenol Content, Physicochemical Parameters and Antioxidant Activity in Beers with Dotted Hawthorn (Crataegus punctata)

Beer with the addition of dotted hawthorn (Crataegus punctata) fruit and juice was prepared and analysed. The content of carbohydrates, glycerol and ethanol in beers was determined by high-performance liquid chromatography (HPLC). Analysis of the total content of polyphenols was also performed using the Folin-Ciocalteu method, as well as determining antioxidant capacity by DPPH^• and ABTS^+• assay, and the ability to reduce iron ions by FRAP assay. Content of volatile compounds was analysed by means of solid-phase microextraction and gas chromatography coupled with mass spectroscopy. Beers with addition of hawthorn, both juice and fruit, had higher antioxidative potential and higher polyphenols concentration compared to control beer. The content of polyphenols in beers was in the range 200.5–410.0 mg GAE/L, and the antioxidant activity was in the range of 0.936–2.04 mmol TE/L (ABTS^+• assay), 0.352–2.175 mmol TE/L (DPPH^• assay) and 0.512–1.35 mmol TE/L (FRAP assay). A sensory evaluation of beers was also carried out. Beer with hawthorn fruit addition obtained the best scores in sensory analysis for criteria such as aroma, taste and overall quality. This beer had the highest content of volatile compounds (287.9 µg/100 mL of beer), while the control beer had lowest concentrations (35.9 µg/100 mL of beer).

Rapid Sensing of Key Quality Components in Black Tea Fermentation Using Electrical Characteristics Coupled to Variables Selection Algorithms

Based on the electrical characteristic detection technology, the quantitative prediction models of sensory score and physical and chemical quality Index (theaflavins, thearubigins, and theabrownins) were established by using the fermented products of Congou black tea as the research object. The variation law of electrical parameters during the process of fermentation and the effects of different standardized pretreatment methods and variable optimization methods on the models were discussed. The results showed that the electrical parameters vary regularly with the test frequency and fermentation time, and the substances that hinder the charge transfer increase gradually during the fermentation process. The Zero-mean normalization (Zscore) preprocessing method had the best noise reduction effect, and the prediction set correlation coefficient (Rp) value of the original data could be increased from 0.172 to 0.842. The mixed variable optimization method (MCUVE-CARS) of Monte Carlo uninformed variable elimination (MC UVE) and competitive adaptive reweighted sampling (CARS) was proved that the characteristic electrical parameters were the loss factor (D) and reactance (X) of the low range. Based on the characteristic variables screened by MCUVE-CARS, the quantitative prediction models for each fermentation quality indicator were established. The Rp values of the sensory score, theaflavin, thearubigin and theabrownins of the predicted models were 0.924, 0.811, 0.85 and 0.938 respectively. The relative percent deviation (RPD) values of the sensory score, theaflavins, thearubigins and theabrownins of the predicted models were 2.593, 1.517, 1,851 and 2.920 respectively, and it showed that these models have good performance and could realize quantitative characterization of key fermentation quality indexes.

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.

Nanomaterial Gas Sensors for Online Monitoring System of Fruit Jams

Jams are appreciated worldwide and have become a growing market, due to the greater attention paid by consumers for healthy food. The selected products for this study represent a segment of the European market that addresses natural products without added sucrose or with a low content of natural sugars. This study aims to identify volatile organic compounds (VOCs) that characterize three flavors of fruit and five recipes using gas chromatography-mass spectrometry (GC-MS) and solid-phase micro-extraction (SPME) analysis. Furthermore, an innovative device, a small sensor system (S3), based on gas sensors with nanomaterials has been used; it may be particularly advantageous in the production line. Results obtained with linear discriminant analysis (LDA) show that S3 can distinguish among the different recipes thanks to the differences in the VOCs that are present in the specimens, as evidenced by the GC-MS analysis. Finally, this study highlights how the thermal processes for obtaining the jam do not alter the natural properties of the fruit.

Volatile components and nutritional qualities of Viscum articulatum Burm.f. parasitic on ancient tea trees

Volatile flavor compounds (VFCs) and nutrients in Viscum articulatum Burm.f. parasitic on ancient tea trees (named TM) were studied in this research by headspace solid-phase microextraction (HS-SPME)/gas chromatography-mass spectrometry (GC-MS) and conventional methods. Sixty-six volatile compounds belonging to different classes were identified by GC-MS. The ketones, alcohols, and aldehydes were the principal aroma groups in TM according to principle component analysis (PCA). The most abundant aroma components in TM included benzaldehyde (9.64%), geranylacetone (7.92%), epoxy-β-ionone (7.71%), β-linalool (7.35%), methyl salicylate (6.96%), and hotrienol (6.14%), significantly higher than CKs (p < .05). The positive PC1 and PC2 in TM were correlated with benzaldehyde, hotrienol, methyl salicylate, and geranylacetone. The mistletoes could be differentiated from CKs due to the difference in aroma compounds. Clean and fresh, woody and nutty odor with minor floral scent was the characteristics of TM. Analysis of the nutritional components showed that contents of polyphenols and catechins in TM were at trace levels, significantly lower than CKs (p < .05). The total contents of polyphenols, amino acids, carbohydrates, and caffeine in TM were significantly lower from the total soluble solids (p < .05), indicating that there were still lots of compounds undetected in TM. The sensory test showed that the taste and aroma in TM can be accepted, which indicates TM could be developed into alternative tea drinks in the future.

A comparative analysis for the volatile compounds of various Chinese dark teas using combinatory metabolomics and fungal solid-state fermentation

A total of 98 compounds including 20 aldehydes, eight arenes, six acids, 17 alcohols, 13 ketones, nine esters, nine methoxyphenolics, three alkenes, seven alkanes, and six other components were tentatively identified in six Chinese dark teas (CDTs) using gas chromatography–mass spectrometry. Multivariate statistical analysis revealed that dark teas from Yunnan and Guangxi provinces could be classified into one group, and other CDTs belonged to the other cluster. The diagnostic volatile compounds being responsible for CDTs' discrimination were observed as (E,E)-2,4-decadienal, methoxyphenolics, geraniol, α-terpineol, 2,4-heptadienal, cis-jasmone, linalool oxides, and 2-nonenal. Furthermore, mature tea leaves were separately fermented using Eurotium cristatum and Aspergillus niger. The results showed that E. cristatum increased the contents of cis-jasmone, α-terpineol, ß-ionone, nonanal, and 2-pentylfuran, whereas A. niger advanced the levels of geraniol, linalool oxides, 9,12-octadecadienoic acid, and ß-ionone after short-term fermentation. Fungus species may contribute to forming the flavor of Chinese dark teas by affecting the volatile compounds during postfermentation.

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.

The study of fingerprint characteristics of Dayi Pu-Erh tea using a fully automatic HS-SPME/GC-MS and combined chemometrics method

The quality of tea is presently evaluated by the sensory assessment of professional tea tasters, however, this approach is both inconsistent and inaccurate. A more standardized and efficient method is urgently needed to objectively evaluate tea quality. In this study, the chemical fingerprint of 7 different Dayi Pu-erh tea brands and 3 different Ya'an tea brands on the market were analyzed using fully automatic headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC–MS). A total of 78 volatiles were separated, among 75 volatiles were identified by GC–MS in seven Dayi Pu-erh teas, and the major chemical components included methoxyphenolic compounds, hydrocarbons, and alcohol compounds, such as 1,2,3-trimethoxybenzene, 1,2,4-trimethoxybenzene, 2,6,10,14-tetramethyl-pentadecane, linalool and its oxides, α-terpineol, and phytol. The overlapping ratio of peaks (ORP) of the chromatogram in the seven Dayi Pu-erh tea samples was greater than 89.55%, whereas the ORP of Ya'an tea samples was less than 79.10%. The similarity and differences of the Dayi Pu-erh tea samples were also characterized using correlation coefficient similarity and principal component analysis (PCA). The results showed that the correlation coefficient of similarity of the seven Dayi Pu-erh tea samples was greater than 0.820 and was gathered in a specific area, which showed that samples from different brands were basically the same, despite have some slightly differences of chemical indexes was found. These results showed that the GC-MS fingerprint combined with the PCA approach can be used as an effective tool for the quality assessment and control of Pu-erh tea.

Gas chromatography analysis with olfactometric detection (GC-O) as a useful methodology for chemical characterization of odorous compounds

The gas chromatography-olfactometry (GC-O) technique couples traditional gas chromatographic analysis with sensory detection in order to study complex mixtures of odorous substances and to identify odor active compounds. The GC-O technique is already widely used for the evaluation of food aromas and its application in environmental fields is increasing, thus moving the odor emission assessment from the solely olfactometric evaluations to the characterization of the volatile components responsible for odor nuisance. The aim of this paper is to describe the state of the art of gas chromatography-olfactometry methodology, considering the different approaches regarding the operational conditions and the different methods for evaluating the olfactometric detection of odor compounds. The potentials of GC-O are described highlighting the improvements in this methodology relative to other conventional approaches used for odor detection, such as sensoristic, sensorial and the traditional gas chromatographic methods. The paper also provides an examination of the different fields of application of the GC-O, principally related to fragrances and food aromas, odor nuisance produced by anthropic activities and odorous compounds emitted by materials and medical applications.