Rapid and direct volatile compound profiling of black and green teas (Camellia sinensis) from different countries with PTR-ToF-MS

Differentiation of black tea according to country of origin using the μ-CTE/TD/GC-MS method combined with decision tree-optimizable neural network analysis

BACKGROUND

Accurate discrimination of the country of origin of teas is critical to determine their actual commercial value, to meet consumer preferences, and to ensure compliance with labeling regulations. Therefore, in this study, we developed a new approach to accurately discriminate the country of origin of teas in the Turkish market.

RESULTS

A thermal desorption/gas chromatographic-mass spectrometric (TD/GC-MS) method combined with optimizable neural networks (ONN) was developed to analyze the volatile organic compounds (VOCs) of tea samples subjected to infusion or grinding pretreatments. Prior to GC-MS analysis, the conventional thermal desorption method was applied to VOCs in the powdered teas, while VOCs in the infused teas were adsorbed on Tenax-TA sorbent tubes attached to a micro-chamber/thermal extractor (μ-CTE) and then thermally desorbed. Using a feature selection technique, a total of 11 VOCs from infused tea samples, 21 VOCs from ground tea samples, and 18 VOCs from both groups were identified as specific VOCs that critically affect the classification of the teas. As a result of ONN classification of selected VOCs from only ground tea samples and infused tea samples, 95.51% and 96.7% accuracy was obtained, respectively, while 100% classification accuracy was achieved by ONN classification of VOCs from both sample groups.

CONCLUSION

The results showed that different pretreatments applied to Turkish and Ceylon teas caused the release of different volatile compounds, resulting in more specific VOC profiles. In addition, the developed μ-CTE/TD/GC-MS method allowed a more accurate classification of the black tea samples than the TD/GC-MS system alone. © 2025 Society of Chemical Industry.

Recalibrating Olfactory Neuroscience to the Range of Naturally Occurring Odor Concentrations

Sensory systems enable organisms to detect and respond to environmental signals relevant for their survival and reproduction. A crucial aspect of any sensory signal is its intensity; understanding how sensory signals guide behavior requires probing sensory system function across the range of stimulus intensities naturally experienced by an organism. In olfaction, defining the range of natural odorant concentrations is difficult. Odors are complex mixtures of airborne chemicals emitting from a source in an irregular pattern that varies across time and space, necessitating specialized methods to obtain an accurate measurement of concentration. Perhaps as a result, experimentalists often choose stimulus concentrations based on empirical considerations rather than with respect to ecological or behavioral context. Here, we attempt to determine naturally relevant concentration ranges for olfactory stimuli by reviewing and integrating data from diverse disciplines. We compare odorant concentrations used in experimental studies in rodents and insects with those reported in different settings including ambient natural environments, the headspace of natural sources, and within the sources themselves. We also compare these values to psychophysical measurements of odorant detection threshold in rodents, where thresholds have been extensively measured. Odorant concentrations in natural regimes rarely exceed a few parts per billion, while most experimental studies investigating olfactory coding and behavior exceed these concentrations by several orders of magnitude. We discuss the implications of this mismatch and the importance of testing odorants in their natural concentration range for understanding neural mechanisms underlying olfactory sensation and odor-guided behaviors.

Effects of Different Kinds of Fruit Juice on Flavor Quality and Hypoglycemic Activity of Black Tea

At present, the heavy bitter taste, poor flavor quality and low functional activity of summer and autumn tea are the bottleneck problems restricting the low utilization rate of summer and autumn tea resources. The research and development of new products of fruit-flavored black tea is conducive to expanding the utilization of summer and autumn tea resources. Different kinds of fruit juice were added during the fermentation and processing of classic black tea, such as bananas, apples, fragrant pear and Sydney pear, in this study. The effects of fruit juice on the flavor quality and amylase inhibitory activity of fruity black tea were researched. The sensory quality, flavor chemicals and α-amylase inhibitory activity were evaluated. The results showed that the sensory evaluation scores of black tea treated with fruit juice were significantly higher than those of black tea treated without fruit juice, especially the crown pear juice. The amylase inhibition rate of black tea treated with fruit juice was significantly higher than the control treated without fruit juice (p < 0.05). The sensory evaluation scores, polyphenol oxidase activity, water extract content, soluble sugar content, free amino acid content, theaflavin content, thearubigin content and inhibition rate of amylase activity of black tea treated with pear juice were significantly higher than those of the apple and banana juices (p < 0.05), especially crown pear juice. Tea polyphenol content and theaflavin content of black tea treated with added pear juice were significantly lower (p < 0.05) than the black tea control treated with added apple juice and banana juice, especially crown pear juice. The fruity black tea treated with crown pear juice had a redder broth, more pronounced sweet fruit aroma, sweet and mellow taste and reduced astringency. Therefore, the black tea treated with crown pear juice was preferred. The research hopes to provide a theoretical basis for the research of black tea quality control and the research of summer and autumn tea resources utilization technology.

Odor-active aroma compounds in traditional fermented dairy products: The case of mabisi in supporting food and nutrition security in Zambia

Aroma is a key sensory attribute that determines consumer preference and acceptability of foods. The aroma of fermented dairy products comprises the volatile organic compounds (VOCs) produced by the activity of fermenting microbes and the compounds originally present in unfermented raw milk. A unique combination of specific compounds detectable by human olfactory senses creates the distinct odor profile of fermented products. This study investigated the influence of different production methods on the VOCs responsible for the odor-active compounds, and the microbial communities present in mabisi, a traditional Zambian fermented dairy product. The VOCs and microbial community composition of four mabisi variants were investigated using GC-O-MS and PTR-QiTOF-MS techniques, and 16S rRNA amplicon sequencing, respectively. A panel of three assessors identified the odor-active compounds from the GC-O-MS, and the compound's quantitative aspects were obtained by the PTR-QiTOF-MS. Twelve volatile compounds were identified as odor-active compounds during the GC-O-MS analysis. The most prominent were ketones and esters, which imparted a buttery and fruity aroma, respectively. The PTR-QiTOF-MS run identified and quantified a total of 390 m/z peaks, 55 of which were tentatively identified. 16S rRNA amplicon sequencing revealed a diverse microbial community, with Lactococcus species dominating. While the VOC profiles showed significant variation in functionality among the variants, minor differences were observed in microbial composition. The study confirms that high compound concentration does not necessarily correlate with compound odor activity. Our findings offer insights into the significance of aromas and microbial ecology to support optimization strategies for upscaling traditional fermented products.

Different smoking processes with the special fuel rods: Impart a smoky aroma to Souchong black tea

The smoky scent is the most distinctive feature for Souchong black tea. To reduce the dependence on pinewood in the smoking process of Souchong black tea, it is crucial to find an effective alternative smoking material. Five black tea samples were prepared via using specially designed fuel rods as the smoking material in this study. Sensory analysis showed that DS (smoking at the drying stage) had the most favorable aroma, featuring a pleasant smoky aroma with floral and fruity notes. 69 volatile compounds were detected in five tested samples. Key volatiles such as β-caryophyllene, nerolidol, guaiacol, and α-terpineol, known for their woody or smoky aroma, were prominent in both DS and TS (the traditional Lapsang Souchong process) samples (OAV > 1, VIP > 1 and P < 0.05). However, DS exhibited significantly lower concentration of these volatiles than TS, giving it a more pleasant aroma. Additionally, phenylethyl alcohol and α-farnesene were characteristic volatiles in FS (smoking at the fermentation stage) and DS, imparting a sweet, mildly smoky aroma. Therefore, using these specialized fuel rods to smoking process at drying stage is an optimal method for processing Souchong black tea. These findings provide a theoretical foundation for stabilizing Souchong black tea quality, promoting green and low-carbon tea production methods.

Comparison of Untargeted and Markers Analysis of Volatile Organic Compounds with SIFT-MS and SPME-GC-MS to Assess Tea Traceability

Tea is one of the most consumed beverages in the world and presents a great aromatic diversity depending on the origin of the production and the transformation process. Volatile organic compounds (VOCs) greatly contribute to the sensory perception of tea and are excellent markers for traceability and quality. In this work, we analyzed the volatile organic compounds (VOCs) emitted by twenty-six perfectly traced samples of tea with two analytical techniques and two data treatment strategies. First, we performed headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) as the most widely used reference method for sanitary and quality controls of food. Next, we analyzed the samples with selected-ion flow-tube mass spectrometry (SIFT-MS), an emerging method for direct analysis of food products and aroma. We compared the performances of both techniques to trace the origin and the transformation processes. We selected the forty-eight most relevant markers with HS-SPME-GC-MS and evaluated their concentrations with a flame ionization detector (FID) on the same instrument. This set of markers permitted separation of the origins of samples but did not allow the samples to be differentiated based on the color. The same set of markers was measured with SIFT-MS instrument without success for either origin separation or color differentiation. Finally, a post-processing treatment of raw data signals with an untargeted approach was applied to the GC-MS and SIFT-MS dataset. This strategy allowed a good discrimination of origin and color with both instruments. Advantages and drawbacks of volatile profiles with both instruments were discussed for the traceability and quality assessment of food.

Determination of Geographical Origin of Southern Shaanxi Congou Black Teas Using Sensory Analysis Combined with Gas Chromatography-Ion Mobility Spectrometry

Southern Shaanxi is one of China's high-quality congou black tea production areas. However, the differences in geography, cultivation, and management techniques and production processes lead to uneven qualities of southern Shaanxi congou black tea in different production areas. This study used sensory analysis combined with gas chromatography-ion mobility spectrometry (GC-IMS) to determine southern Shaanxi congou black teas' geographical origin and volatile fingerprints to prevent economic losses caused by fraudulent labeling. A total of 61 volatile compounds were identified and quantified by GC-IMS. Three main aroma types were found by sensory analysis coupled with significant difference analysis, and a clear correlation between volatile compounds, aroma type, and geographical origin was found by sensory and gallery plot analysis. The black tea with a green/grassy-roast aroma type was mainly distributed in production areas with an altitude of 400-800 m and 1-pentanol, cyclohexanone, 1-penten-3-one, 2-heptanone, dihydroactinidiolide and butyrolactone were the key aroma markers. The black teas produced in production areas with an altitude of 800-1000 m mainly presented strong honey and caramel-like aromas, and sotolone, furaneol, and phenylacetaldehyde played an important role. These results will be helpful for discriminating black tea from different tea production areas in southern Shaanxi.

Long-range infrared absorption spectroscopy and fast mass spectrometry for rapid online measurements of volatile organic compounds from black tea fermentation

Fermentation is the key process to determine the quality of black tea. Traditional physical and chemical analyses are time consuming, it cannot meet the needs of online monitoring. The existing rapid testing techniques cannot determine the specific volatile organic compounds (VOCs) produced at different stages of fermentation, resulting in poor model transferability; therefore, the current degree of black tea fermentation mainly relies on the sensory judgment of tea makers. This study used proton transfer reaction mass spectrometry (PTR-MS) and fourier transform infrared spectroscopy (FTIR) combined with different injection methods to collect VOCs of the samples, the rule of change of specific VOCs was clarified, and the extreme learning machine (ELM) model was established after principal component analysis (PCA), the prediction accuracy reached 95% and 100%, respectively. Finally, different application scenarios of the two technologies in the actual production of black tea are discussed based on their respective advantages.

The behavioral sensitivity of mice to acyclic, monocyclic, and bicyclic monoterpenes

Monoterpenes are a large class of naturally occurring fragrant molecules. These chemicals are commonly used in olfactory studies to survey neural activity and probe the behavioral limits of odor discrimination. Monoterpenes (typically in the form of essential oils) have been used for centuries for therapeutic purposes and have pivotal roles in various biological and medical applications. Despite their importance for multiple lines of research using rodent models and the role of the olfactory system in detecting these volatile chemicals, the murine sensitivity to monoterpenes remains mostly unexplored. We assayed the ability of C57BL/6J mice to detect nine different monoterpenes (the acyclic monoterpenes: geraniol, citral, and linalool; the monocyclic monoterpenes: r-limonene, s-limonene, and γ-terpinene; and the bicyclic monoterpenes: eucalyptol, α-pinene, and β-pinene) using a head-fixed Go / No-Go operant conditioning assay. We found that mice can reliably detect monoterpene concentrations in the low parts per billion (ppb) range. Specifically, mice were most sensitive to geraniol (threshold: 0.7 ppb) and least sensitive to γ-terpinene (threshold: 18.1 ppb). These estimations of sensitivity serve to set the lower limit of relevant monoterpene concentrations for functional experiments in mice. To define an upper limit, we estimated the maximum concentrations that a mouse may experience in nature by collating published headspace analyses of monoterpene concentrations emitted from natural sources. We found that natural monoterpenes concentrations typically ranged from ~1 to 1000 ppb. It is our hope that this dataset will help researchers use appropriate monoterpene concentrations for functional studies and provide context for the vapor-phase delivery of these chemicals in studies investigating their biological activity in mice.

Manufacturing process differences give Keemun black teas their distinctive aromas

Traditional Keemun black tea is also known as Congou black tea (CF). Over the last three decades, three other types of Keemun black tea (Jinzhen, JZ; Maofeng, MF; Xiangluo, XL) made by different processing have been introduced into the tea market. Total CF volatile concentrations ranged from 1666.3 to 2185.7 μg/L, followed by XL (1193.5-1916.1 μg/L), JZ (1058.9-1811.0 μg/L), and MF (987.5-1518.0 μg/L) tea infusions. A total of 79 volatiles in tea infusions was identified by two methods, among which fourteen with OAVs > 1 were identified and OAVs proportion of volatiles with flowery, fruity, or sweet notes to those with other notes differed in four Keemun black teas (CF = 6.58:1, MF = 5.16:1, JZ = 4.04:1, XL = 5.11:1). Phenylethyl alcohol oxidation resulted in phenylacetaldehyde formation which is the characteristic odorant in Keemun black tea. We clearly show that changes in tea processing gives the distinctive aroma to different Keemun black teas.

Online monitoring of higher alcohols and esters throughout beer fermentation by commercial Saccharomyces cerevisiae and Saccharomyces pastorianus yeast

Higher alcohols and esters are among the predominant classes of volatile organic compounds (VOCs) that influence the quality of beer. The concentrations of these compounds are determined through a specific yeast strain selection and fermentation conditions. The effect of yeast strains on the formation of higher alcohols and esters throughout fermentations (at 20°C) was investigated. Flavour-relevant esters (ethyl acetate, isoamyl acetate, ethyl hexanoate and ethyl octanoate) and higher alcohols (isoamyl alcohol, isobutyl alcohol and phenylethyl alcohol) were monitored throughout the fermentation using proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) coupled with an automated sampling system for continuous measurements. Compound identification was confirmed by analysis of samples using gas chromatography-mass spectrometry (GC-MS). Results demonstrated the specific time points where variation in higher alcohol and ester generation between yeast strains occurred. In particular, the concentrations of isoamyl acetate, ethyl octanoate and isoamyl alcohol between yeast strains were significantly different over the first 2 days of fermentation; whereas, after Day 3, no significant differences were observed. The two Saccharomyces pastorianus strains produced comparable concentrations of the key higher alcohols and esters. However, the key higher alcohol and ester concentrations varied greatly between the two S. cerevisiae strains. The use of PTR-ToF-MS to rapidly measure multiple yeast strains provides new insights on fermentation for brewers to modify the sensory profile and optimise quality.

Authenticating teas using multielement signatures, strontium isotope ratios, and volatile compound profiling

High value food products are subject to adulterations and frauds. This study aimed to combine, in our knowledge for the first time, inorganic chemical tracers (multi-elements and Sr isotopy) with volatile organic compound (VOCs) to discriminate the geographic origin, the varieties and transformation processes to authenticate 26 tea samples. By measuring Sr isotope ratio using the multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), 6 out of 11 regions were successfully discriminated. The combination with the ICP-MS inorganic pattern allowed to discriminate 4 more regions with a significance level of 0.05. VOCs fingerprints, obtained with selected ion flow tube mass spectrometer (SIFT-MS), were not correlated with origin but with the cultivar and transformation processes. Green, oolong, and dark teas were clearly differentiated, with hexanal and hexanol contributing to the discrimination of oxidation levels. With this multi-instrumental approach, it is possible to certify the geographical origin and the tea conformity.

Detection of volatile organic compounds in adulterated tea using Fourier transform infrared spectroscopy and Proton-transfer-reaction mass spectrometry

Aroma is a key factor used to evaluate tea quality. Illegal traders usually add essence to expired or substandard tea to improve its aroma so as to gain more profit. Traditional physical and chemical testing methods are time-consuming and costly. Furthermore, rapid detection techniques, such as near-infrared spectroscopy and machine vision, can only be used to detect adulterated powdered solid essences in tea. In this study, proton-transfer reaction mass spectrometry (PTR-MS) and Fourier-transform infrared spectroscopy (FTIR) were employed to detect volatile organic compounds (VOCs) in samples, and rapid detection of different tea adulterated liquid essence was achieved. The prediction accuracies of PTR-MS and FTIR reached over 0.941 and 0.957, respectively, and the minimum detection limits were lower than the actual used values in both. In this study, the different application scenarios of the two technologies are discussed based on their performance characteristics.

Identification of aroma-active compounds responsible for the floral and sweet odors of Congou black teas using gas chromatography-mass spectrometry/olfactometry, odor activity value, and chemometrics

BACKGROUND

Floral and sweet odors are two typical characteristic aromas of Congou black tea, but their aroma-active compounds are still unclear. Characterizing the key aroma-active compounds can provide a theoretical foundation for the practical aroma quality evaluation of Congou black tea and directional processing technology of high-quality black tea with floral or sweet odors. Gas chromatography-olfactometry (GC-O) combined with odor activity value (OAV) is often used to screen key aroma-active substances, but the interaction between aroma components and their impact on the overall sensory quality is ignored. Therefore, in this study, OAV combined with variable importance in projection (VIP) and Spearman correlation analysis (SCA) were used to characterize the aroma-active components of Congou black teas with floral and sweet odors.

RESULTS

Eighty-five volatiles were identified in these samples using gas chromatography-mass spectrometry (GC-MS). Twenty-three compounds were identified as potential markers for the floral and sweet odors of Congou black teas from orthogonal partial least squares discriminant analysis (OPLS-DA). Eighteen compounds were selected as candidate aroma compounds based on GC-O analysis and OAV calculations. In addition, 26 compounds were screened as crucial aroma compounds based on SCA. Finally, 19 compounds were evaluated as key aroma compounds by the comprehensive evaluation of VIP, OAV, and SCA. Terpenoids are the main active compounds that contribute to the floral odor of Congou black tea, whereas aldehydes are the key compounds for the sweet odor.

CONCLUSION

The proposed method can effectively screen the aroma-active compounds and can be used for comprehensive quality control of products. © 2022 Society of Chemical Industry.

Measuring volatile emissions from moss gametophytes: A review of methodologies and new applications

Mosses inhabit nearly all terrestrial ecosystems and engage in important interactions with nitrogen-fixing microbes, sperm-dispersing arthropods, and other plants. It is hypothesized that these interactions could be mediated by biogenic volatile organic compounds (BVOCs). Moss BVOCs may play fundamental roles in influencing local ecologies, such as biosphere-atmosphere-hydrosphere communications, physiological and evolutionary dynamics, plant-microbe interactions, and gametophyte stress physiology. Further progress in quantifying the composition, magnitude, and variability of moss BVOC emissions, and their response to environmental drivers and metabolic requirements, is limited by methodological and analytical challenges. We review several sampling techniques with various analytical approaches and describe best practices in generating moss gametophyte BVOC measures. We emphasize the importance of characterizing the composition and magnitude of moss BVOC emissions across a variety of species to better inform and stimulate important cross-disciplinary studies. We conclude by highlighting how current methods could be employed, as well as best practices for choosing methodologies.

Identification of the age of white tea using proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) coupled with multivariate analysis

RATIONALE

In recent years, white tea has become increasingly popular. Some merchants confuse the age of white tea and sell poor-quality products for profit. Therefore, it is necessary to provide technical support for product authentication and valorization in white tea of different marked ages.

METHODS

Volatile organic compounds (VOCs) were detected by proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) and identified as volatile fingerprints. PTR-TOF-MS combined with multivariate analysis was found to identify white tea of four different marked ages (1, 3, 5, and 8 years) for authentication. Principal component analysis (PCA) and orthogonal partial least-squares discriminant analysis (OPLS-DA) were used as classification models to identify key volatile metabolites.

RESULTS

The OPLS-DA model achieved the best results (96.67%, 96.67%, 96.67%, and 96.67% in the training set and 96.00%, 96.00%, 100%, and 100% in the prediction set for 1-year, 3-year, 5-year, and 8-year tea samples, respectively), showing that PTR-TOF-MS with the OPLS-DA model could successfully be used in the identification of white tea with different marked ages. Out of the 60 identified VOCs, 26 volatile materials were closely correlated with tea age and were used as markers to discriminate white tea of different ages.

CONCLUSIONS

PTR-TOF-MS coupled with multivariate analysis could be applied for quality evaluation of tea products of different ages and provided a feasible technical support for product authentication and valorization in white tea of different marked ages.

Recent techniques for the authentication of the geographical origin of tea leaves from camellia sinensis: A review

Tea is one of the most important beverages worldwide, is produced in several distinct geographical regions, and is traded on the global market. The ability to determine the geographical origin of tea products helps to ensure authenticity and traceability. This paper reviews the recent research on authentication of tea using a combination of instrumental and chemometric methods. To determine the production region of a tea sample, instrumental methods based on analyzing isotope and mineral element contents are suitable because they are less affected by tea variety and processing methods. Chemometric analysis has proven to be a valuable method to identify tea. Principal component analysis (PCA) and linear discriminant analysis (LDA) are the most preferred methods for processing large amounts of data obtained through instrumental component analysis.

Online Monitoring the Key Intermediates and Volatile Compounds Evolved from Green Tea Roasting by Synchrotron Radiation Photoionization Mass Spectrometry

Online monitoring of the volatile compounds during the tea roasting process is crucial to find the optimum roasting conditions and improve the quality of green tea. In this work, synchrotron radiation photoionization mass spectrometry (SR-PIMS) was utilized to online monitor the evolved gaseous compounds during the tea roasting process. By virtue of "soft" ionization and fast data acquisition characteristics of SR-PIMS, dozens of aroma compounds including alcohols, aldehydes, furans, and nitrogen- and sulfur-containing species were detected and identified in real time. Moreover, 5-hydroxymethylfurfural (5-HMF), the key intermediate of Maillard reactions, was found with high sensitivity. Evolution processes of all the products could be observed via the time- and temperature-resolved profiles in N₂ and the air. Dehydration was found to be the first step during roasting. Oxygen in the air was found to accelerate the formation rate of various stable species and intermediates in the course of the thermal treatment of fresh green tea. The formation mechanisms of evolved compounds such as three sulfur-containing compounds, i.e., dimethyl sulfide, hydrogen sulfide, and methanethiol, could be proposed according to the step-by-step formation process. The time-resolved results were demonstrated to be applicable in the evaluation of different roasting processes by statistical analysis. The optimum tea roasting temperature and duration are proposed to be around 200 °C and 1000 s.

Identification of the volatile profiles of 22 traditional and newly bred maize varieties and their porridges by PTR-QiTOF-MS and HS-SPME GC-MS

BACKGROUND

Low adoption of maize varieties bred to address the nutritional needs of the growing African population limits their impact. Aroma is essential in consumer preference, but has hitherto hardly been studied. We analysed the volatile organic compounds of flours and porridges of 22 maize varieties belonging to four nutritionally distinct groups, namely provitamin A maize, quality protein maize, yellow and white maize.

RESULTS

Proton-transfer-reaction quadrupole ion time-of-flight mass spectrometry (PTR-QiTOF-MS) analysis generated 524 mass peaks ranging from 16.007 to 448.089 m/z. Principal component analysis separated the varieties belonging to the four groups. With headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME GC-MS), 48 volatile compounds were identified in maize flour and 21 in maize porridge, including hexane, nonane, pentanoic acid, 1-octen-3-ol, 1-hexanol, hexanal, nonanal, 2-pentylfuran and 2-heptanone. Volatile compounds such as 1,2,4-trimethyl benzene, associated with thermal degradation of carotenoids, increased in the porridge of yellow and provitamin A maize.

CONCLUSION

The results indicate that PTR-QiTOF-MS and HS-SPME GC-MS combined with multivariate analysis are instrumental to study the volatile aroma compounds of different maize varieties.

Absolute Quantitative Volatile Measurement from Fresh Tea Leaves and the Derived Teas Revealed Contributions of Postharvest Synthesis of Endogenous Volatiles for the Aroma Quality of Made Teas

Characteristic aroma is a well-appreciated feature contributing to tea quality. Although extensive studies have been made to investigate aroma biosynthesis and gene expressions during tea making processes, it remains unclear whether the endogenous volatile biosynthesis during postharvest tea processing contributes to the aroma quality of made tea. To critically evaluate this question, we used the same batch of fresh tea leaves and produced three different types of tea with different degrees of fermentation (green tea, oolong tea, and black tea). Total volatiles were extracted by solvent-assisted-flavor evaporation, then quantified by gas chromatography-flame ionization detector combined with response factor correction for quantitative measurement. Compared with fresh tea leaves, the volatile profiles of the made teas were dramatically altered, with significant loss for the majority of endogenous volatiles and simultaneous gain for non-endogenous volatiles. By calculation of odor-activity values, the potential volatiles contributing to the aroma characteristics of each tea type were identified. Our data suggest that postharvest synthesis of endogenous volatiles did not contribute to the aroma quality of made tea.

Rapid and direct identification of the origin of white tea with proton transfer reaction time-of-flight mass spectrometry

RATIONALE

White tea has become very popular in recent years, but there has been no scientific identification of white tea from different origins. For product authentication and valorization, every kind of white tea must be marked with an indication of its origin.

METHODS

Volatile profiles of white tea leaf samples from their main origins in China (Fuding City, Zhenghe City and Jianyang City) were analyzed using proton transfer reaction time-of-flight mass spectrometry (PTR-TOFMS). Tentative identifications of the volatile organic compounds (VOCs) were obtained by PTR-TOFMS of the headspace. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were performed to evaluate the differences among the various origins.

RESULTS

Teas from different origins were shown to have characteristic VOCs and profiles. Thus, white teas from different origins could be separated by characterizing the volatile emissions from the dry tea leaves. The ability of the two classification models to use the volatile fingerprints in origin discrimination was investigated.

CONCLUSIONS

Two classification models (PCA and OPLS-DA) were applied to the PTR-TOFMS data obtained from the VOCs of various white teas. The classification models were shown to be useful in identifying the origin of white tea samples, providing a reference for white tea identification.

Differentiating Westlake Longjing tea from the first- and second-grade producing regions using ultra high performance liquid chromatography with quadrupole time-of-flight mass spectrometry-based untargeted metabolomics in combination with chemometrics

There are numerous articles published for geographical discrimination of tea. However, few research works focused on the authentication and traceability of Westlake Longjing green tea from the first- and second-grade producing regions because the tea trees are planted in a limited growing zone with identical cultivate condition. In this work, a comprehensive analytical strategy was proposed by ultrahigh performance liquid chromatography-quadrupole time-of-flight mass spectrometry-based untargeted metabolomics coupled with chemometrics. The automatic untargeted data analysis strategy was introduced to screen metabolites that expressed significantly among different regions. Chromatographic features of metabolites can be automatically and efficiently extracted and registered. Meanwhile, those that were valuable for geographical origin discrimination were screened based on statistical analysis and contents in samples. Metabolite identification was performed based on high-resolution mass values and tandem mass spectra of screened peaks. Twenty metabolites were identified, based on which the two-way encoding partial least squares discrimination analysis was built for geographical origin prediction. Monte Caro simulation results indicated that prediction accuracy was up to 99%. Our strategy can be applicable for practical applications in the quality control of Westlake Longjing green tea.

From Extra Virgin Olive Oil to Refined Products: Intensity and Balance Shifts of the Volatile Compounds versus Odor

To explore relationships between the volatile organic compounds (VOCs) of different grades of olive oils (OOs) (extra virgin olive oil (EVOO), refined olive oil (ROO), and pomace olive oil (POO)) and odor quality, VOCs were measured in the headspace of the oils by proton transfer reaction quadrupole ion guide time-of-flight mass spectrometry. The concentrations of most VOCs differed significantly between the grades (EVOO > ROO > POO), whereas the abundance of m/z 47.012 (formic acid), m/z 49.016 (fragments), m/z 49.027 (fragments), and m/z 115.111 (heptanal/heptanone) increased in that order. Although the refined oils had considerably lower VOC abundance, the extent of the decline varied with the VOCs. This results in differences in VOCs proportions. The high VOC abundance in the EVOO headspace in comparison to ROO and POO results in a richer and more complex odor. The identified C5–C6 compounds are expected to contribute mainly to the green odor notes, while the identified C1–C4 and C7–C15 are mainly responsible for odor defects of OOs. Current results reveal that processing strongly affects both the quantitative and relative abundance of the VOCs and, therefore, the odor quality of the various grades of OOs.

Real-Time Volatilomics: A Novel Approach for Analyzing Biological Samples

The use of the 'omics techniques in environmental research has become common-place. The most widely implemented of these include metabolomics, proteomics, genomics, and transcriptomics. In recent years, a similar approach has also been taken with the analysis of volatiles from biological samples, giving rise to the so-called 'volatilomics' in plant analysis. Developments in direct infusion mass spectrometry (DI-MS) techniques have made it possible to monitor the changes in the composition of volatile flux from parts of plants, single specimens, and entire ecosystems in real-time. The application of these techniques enables a unique insight into the dynamic metabolic processes that occur in plants. Here, we provide an overview of the use of DI-MS in real-time volatilomics research involving plants.

Application of apigeninidin-rich red sorghum biocolorant in a fermented food improves product quality

BACKGROUND

The 'clean label' trend is pushing the food industry to replace synthetic colorants with plant-based colorants. However, technological efficacy and undesirable side effects restrict the use of plant-based colorants in industrial applications. This research studied the production of fermented maize dough coloured by apigeninidin-rich red sorghum biocolorant, as practised for centuries in West Africa, as a model to assess the impact of the biocolorant on nutritional and sensorial quality of foods.

RESULTS

A 3-day fermentation of a dyed maize dough (containing 327 µg g-1 dry matter of apigeninidin) by Pichia kudriavzevii and Lactobacillus fermentum led to a degradation of 69% of the apigeninidin content, causing a clearly visible colour difference (ΔE*00 17.4). The antioxidant activity of fermented dyed dough (DD) increased by 51% compared to fermented non-dyed dough (NDD). However, the phytate dephosphorylation and volatile organic compound concentrations were lower in DD than in NDD. This suggests a lower mineral solubility and change in the sensory quality of fermented DD.

CONCLUSION

Apigeninidin extract from sorghum leaf sheaths proved to be a bioactive red biocolorant with potential in fermented foods. The formation of new antioxidant compounds needs further investigation, as does the impact on the development of volatile compounds. © 2018 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Characterization of the volatile components in green tea by IRAE-HS-SPME/GC-MS combined with multivariate analysis

In the present work, a novel infrared-assisted extraction coupled to headspace solid-phase microextraction (IRAE-HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS) was developed for rapid determination of the volatile components in green tea. The extraction parameters such as fiber type, sample amount, infrared power, extraction time, and infrared lamp distance were optimized by orthogonal experimental design. Under optimum conditions, a total of 82 volatile compounds in 21 green tea samples from different geographical origins were identified. Compared with classical water-bath heating, the proposed technique has remarkable advantages of considerably reducing the analytical time and high efficiency. In addition, an effective classification of green teas based on their volatile profiles was achieved by partial least square-discriminant analysis (PLS-DA) and hierarchical clustering analysis (HCA). Furthermore, the application of a dual criterion based on the variable importance in the projection (VIP) values of the PLS-DA models and on the category from one-way univariate analysis (ANOVA) allowed the identification of 12 potential volatile markers, which were considered to make the most important contribution to the discrimination of the samples. The results suggest that IRAE-HS-SPME/GC-MS technique combined with multivariate analysis offers a valuable tool to assess geographical traceability of different tea varieties.

Ozone-induced foliar damage and release of stress volatiles is highly dependent on stomatal openness and priming by low-level ozone exposure in Phaseolus vulgaris

Acute ozone exposure triggers major emissions of volatile organic compounds (VOCs), but quantitatively, it is unclear how different ozone doses alter the start and the total amount of these emissions, and the induction rate of different stress volatiles. It is also unclear whether priming (i.e. pre-exposure to lower O3 concentrations) can modify the magnitude and kinetics of volatile emissions. We investigated photosynthetic characteristics and VOC emissions in Phaseolus vulgaris following acute ozone exposure (600 nmol mol-1 for 30 min) under illumination and in darkness and after priming with 200 nmol mol-1 O3 for 30 min. Methanol and lipoxygenase (LOX) pathway product emissions were induced rapidly, followed by moderate emissions of methyl salicylate (MeSA). Stomatal conductance prior to acute exposure was lower in darkness and after low O3 priming than in light and without priming. After low O3 priming, no MeSA and lower LOX emissions were detected under acute exposure. Overall, maximum emission rates and the total amount of emitted LOX products and methanol were quantitatively correlated with total stomatal ozone uptake. These results indicate that different stress volatiles scale differently with ozone dose and highlight the key role of stomatal conductance in controlling ozone uptake, leaf injury and volatile release.

Identification of Chinese Herbal Medicines with Electronic Nose Technology: Applications and Challenges

This paper provides a review of the most recent works in machine olfaction as applied to the identification of Chinese Herbal Medicines (CHMs). Due to the wide variety of CHMs, the complexity of growing sources and the diverse specifications of herb components, the quality control of CHMs is a challenging issue. Much research has demonstrated that an electronic nose (E-nose) as an advanced machine olfaction system, can overcome this challenge through identification of the complex odors of CHMs. E-nose technology, with better usability, high sensitivity, real-time detection and non-destructive features has shown better performance in comparison with other analytical techniques such as gas chromatography-mass spectrometry (GC-MS). Although there has been immense development of E-nose techniques in other applications, there are limited reports on the application of E-noses for the quality control of CHMs. The aim of current study is to review practical implementation and advantages of E-noses for robust and effective odor identification of CHMs. It covers the use of E-nose technology to study the effects of growing regions, identification methods, production procedures and storage time on CHMs. Moreover, the challenges and applications of E-nose for CHM identification are investigated. Based on the advancement in E-nose technology, odor may become a new quantitative index for quality control of CHMs and drug discovery. It was also found that more research could be done in the area of odor standardization and odor reproduction for remote sensing.