Influence of fixation methods on the chestnut-like aroma of green tea and dynamics of key aroma substances

Effect of Blue Light Intensity During Spreading on the Aroma of Green Tea

Spreading is the key process for ensuring green tea quality. However, the effect of blue light intensity conditions on the formation of green tea aroma and the evolution of key volatile compounds has not been assessed to date. Four tea samples treated with different light conditions (blue light intensities) were used to investigate the effect of spreading treatment on changes in the composition and content of volatile compounds. Volatile compounds in green tea samples were detected using headspace-solid phase microextraction and gas chromatography-mass spectrometry under different light conditions. Orthogonal partial least squares discriminant analysis (OPLS-DA) and relative odor activity value (rOAV) analyses were then applied to clarify the best blue light condition for forming aroma and associated compounds. The 116 volatile compounds were detected in the green tea samples, of which alcohols were the most abundant. The findings demonstrated that MBL (middle-intensity blue light; 150 μmol/(m2∙s)) treatment was the most effective condition for developing an intense and persistent fruity and floral scent compared to HBL (high-intensity blue light; 300 μmol/(m2∙s)) and LBL (low-intensity blue light; 75 μmol/(m2∙s)). This study underscores how blue light intensity conditions shape green tea aromas and offers operational insights. It also provides a theoretical basis for controlling light conditions in the process of green tea spreading.

Study of Laurie tea processor black tea mixing fermentation using the simplex centroid design method

BACKGROUND

Broken black tea (BBT) is the most consumed black tea in the world. Laurie tea processor black tea (LTP-BT) is one of the most important categories of BBT. In this study, the fresh leaves of three tea plant cultivars including Golden Peony tea, Yunnandaye, and Fuding Dabai were blended to process LTP-BT using the simplex centroid design. Using gas chromatography-mass spectrometry and high-performance liquid chromatography, the differences in volatile and non-volatile components of LTP-BT under different formulations were analyzed.

RESULTS

A total of 88 volatile compounds were detected, among which 16 aroma compounds, including benzyl alcohol, linalool, and methyl salicylate, could be identified as key common aroma substances in BBT. Following evaluation of the model, Golden Peony 16.7%, Fuding Dabai 16.7%, and Yunnan Daye 67.8% were the best proportions in mixed fermentation of LTP-BT. The LTP-BT produced in this ratio had a high and lasting aroma, strong and mellow taste, and bright and red soup color.

CONCLUSION

Our study showed that mixed fermentation is feasible for the manufacturing process of LTP-BT, and the simplex centroid design would be a reliable guide for cultivar formulation, providing customers with an alterable flavor and consumption feature. © 2024 Society of Chemical Industry.

Effects of fermented tea by Aspergillus cristatus on the characteristic aroma and non-volatile components of Jiang-flavor baijiu

BACKGROUND

Fu Brick tea (FBT) extract has been demonstrated to lower blood lipids, protect liver, and prevent obesity. Despite these benefits, there are no products on the market that combine FBT with other foods or beverages.

RESULT

In this study, we developed a novel product by combining FBT with high-alcohol Jiang-flavor baijiu, resulting in FBT-baijiu. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis revealed that FBT-baijiu contains health-promoting alkaloids, including eurocristatine (13.60 ± 0.13 mg/L), (-)-neoechinulin A (10.26 ± 0.09 mg/L), neoechinulin D (7.89 ± 0.05 mg/L), variecolorin G (6.94 ± 0.05 mg/L), and echinulin (25.46 ± 0.27 mg/L), which are known to be present in FBT. The aroma compounds of the FBT-baijiu and the base baijiu were analyzed using comprehensive gas chromatography-olfactometry-mass spectrometry (GC-O-MS) technology. The major volatile compounds of two baijiu samples were identified using relative odor activity values (r-OAVs) analysis. The FBT-baijiu showed a significant reduction in ester content, but a remarkable enhancement in aromatic properties. The findings show that combining FBT with baijiu not only offers functional components but also enhances the flavor profile.

CONCLUSION

This study highlights the potential of utilizing FBT as a functional food ingredient or additive, paving the way for the development of new health-promoting products. © 2024 Society of Chemical Industry.

Dynamic changes in chemical components, volatile profile and antioxidant properties of Xanthoceras sorbifolium leaf tea during manufacturing process

In order to elucidate the dynamic changes of quality characteristics in Xanthoceras sorbifolium leaf tea (XLT), this work investigated the chemical components, volatile profile, and antioxidant properties at key stages of fixation, shaping, and drying. The process of fixation and drying emerged as critical stages that affected the chemical components and taste of XLT. Total polyphenols, reducing sugars and chlorophyll were the differential compounds, which decreased by 29.1 %, 63.3 % and 69.5 % during processing, respectively. Threonine, glycine, arginine, reducing sugar, caffeine, catechin (C), and epicatechin gallate (ECG) were primary taste characteristic compounds. A total of 95 volatile organic components (VOCs) and 24 key odorants with relative odor activity value (ROAV) > 1.0 were identified in XLT, ethyl 2-methylbutanoate-D, dimethyl disulfide, and ethyl isobutyrate (ROAV = 100) were the central contributors to volatiles profile. Moreover, tea manufacturing enhanced the antioxidant potency composite (APC) by 1.1 %, primarily due to its high water extract content.

Effects of Roasting Process on Sensory Qualities, Color, Physicochemical Components, and Identification of Key Aroma Compounds in Hubei Strip-Shaped Green Tea

BACKGROUND

Roasting conditions significantly influence the sensory profile of Hubei strip-shaped green tea (HSSGT).

METHODS

This study examined the effects of roast processing on the sensory attributes, color qualities, physicochemical properties, and key aroma compounds of HSSGT. Sensory evaluation, color qualities determination, principal component analysis of physicochemical components (PCA), HS-SPME (headspace solid-phase microextraction) coupled with GC-MS (gas chromatography-mass spectrometry), relative odor activity value (ROAV), gas chromatography-olfactometry (GC-O), and absolute quantification analysis were employed to identify the critical difference in compounds that influence HSSGT desirability.

RESULTS

The results indicated that HSSGT roasted at 110 °C for 14 min achieved the highest sensory scores, superior physicochemical qualities, and an enhanced aroma index, which was attributed to shifting the proportion of chestnut to floral volatile compounds. Additionally, sensory-guided ROAV, GC-O, and absolute quantification revealed that linalool, octanal, nonanal, and hexanal were the most significant volatile compounds. The variations in these four critical compounds throughout the roasting process were further elucidated, showing that the ideal roasting conditions heightened floral aromas while diminishing the presence of less desirable green odors. These findings offer technical guidance and theoretical support for producing HSSGT with a more desirable balance of chestnut and floral aroma characteristics.

A robust deep learning model for predicting green tea moisture content during fixation using near-infrared spectroscopy: Integration of multi-scale feature fusion and attention mechanisms

Fixation is a critical step in green tea processing, and the moisture content of the leaves after fixation is a key indicator of the fixation quality. Near-infrared spectroscopy (NIRS)-based moisture detection technology is often applied in the tea processing industry. However, temperature fluctuations during processing can cause changes in the NIRS curves, which in turn affect the accuracy of moisture prediction models based on the spectral data. To address this challenge, NIRS data were collected from samples at various stages of fixation and at different temperatures, and a novel deep learning network (DiSENet) was proposed, which integrates multi-scale feature fusion and attention mechanisms. Using a global modeling approach, the proposed method achieved a coefficient of determination (RP2) of 0.781 for moisture content prediction, with a root mean square error (RMSEP) of 1.720 % and a residual predictive deviation (RPD) of 2.148. On the dataset constructed for this study, DiSENet demonstrated superior predictive accuracy compared to the spectral correction methods of external parameter orthogonalization (EPO) and generalized least squares weighting (GLSW), as well as traditional global modeling methods such as partial least squares regression (PLSR) and support vector regression (SVR). This approach effectively corrects spectral interferences caused by temperature variations, thereby enhancing the accuracy of moisture content prediction. Thus, it offers a reliable solution for real-time, non-destructive moisture detection during tea processing.

The aroma formation from fresh tea leaves of Longjing 43 to finished Enshi Yulu tea at an industrial scale

BACKGROUND

Enshi Yulu tea (ESYL) is the most representative of steamed green tea in China, but its aroma formation in processing is unclear. Thus, the ESYL volatiles during the whole industrial processing were investigated using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry.

RESULTS

A total of 134 volatiles were identified. Among these, 31 differential volatiles [P < 0.05 and variable importance in projection (VIP) > 1] and 25 key volatiles [relative odor activity value (rOAV) and/or the ratio of each rOAV to the maximum rOAV (ROAV) > 1.0] were screened out, wherein β-ionone and nonanal were the most key odorants. Besides, the sensory evaluation combined with multivariate statistical analysis of volatiles pinpointed spreading, fixation, first drying, and second drying as the key processing steps that have a pronounced influence on the aroma quality of ESYL. Furthermore, the oxidative degradation of unsaturated fatty acids, synthesis of monoterpenes, and degradation of carotenoids were the main metabolic pathway for the formation of key odorants.

CONCLUSION

The study provides comprehensive insights into the volatile characteristics during the industrial processing of ESYL and promote our understanding of the aroma formation in steamed green teas. © 2024 Society of Chemical Industry.

Analysis of the Changes in Volatile Components During the Processing of Enshi Yulu Tea

Volatile constituents are critical to the flavor of tea, but the changes in Enshi Yulu tea during the processing have not been clearly understood. Using headspace solid phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME/GC-MS) techniques, we analyze the aroma components of Enshi Yulu tea and changes in them during the processing stages. In total, 242 volatile compounds were identified. From fresh leaves to the shaping process in tea production, there are significant decreases in overall aroma substances, followed by increases after drying. Linalool is the dominant aroma component in Enshi Yulu tea, with a proportion of 12.35%, followed by compounds such as geraniol (7.41%), 2,6-dimethyl-5-heptene (6.93%), phenylmethanol (5.98%), isobutyl acetate (4.16%), hexan-1-ol (3.95%), 2-phenylacetaldehyde (3.80%), and oct-1-ene-3-ol (3.34%). The number of differential volatile components varied by production stage, with 20 up- and 139 down-regulated after steaming, 24 down-regulated after rolling, 60 up- and 51 down-regulated after shaping, and 68 up- and 13 down-regulated after drying. Most variation in expression occurred because of steaming, and the least during the rolling stage. PLS-DA analysis revealed significant differences in aroma components throughout processing and the identification of 100 compounds with higher relative contents, with five distinct change trends. Phenylmethanol, phenylacetaldehyde, (2E)-non-2-enal, oct-1-ene-3-ol, and cis-3-hexenyl hexanoate could exert a profound influence on the overall aroma quality of Enshi Yulu tea during processing. The results offer a scientific foundation and valuable insights for understanding the volatile composition of Enshi Yulu tea and its changes during the processing.

Icewine fingerprint involved in latitude under climate change

Aroma plays a crucial role in determining icewine quality and influencing the profit of growers, but the influence of climate change on icewine sustainable production and the diversity of aroma volatiles in icewine among different regions are unknown. Here, we employed aroma volatiles of 8 Vidal icewines from 2 typical premium production regions (Liaoning in China and Ontario in Canada) and an emerging low-latitude mountainous area (Yunnan in China) to project future diversity and sustainability. We found that Ontario and Yunnan's icewines were characterized with intense apricot or peach and tropical fruit aromas, which was consistent with the excellent grade icewine around the world based on 225 icewine aroma datasets from 5 countries. Icewine from Liaoning was abundant with honey flavor. Moreover, projections suggested a northward trend of 3.5° N and 6° N in Ontario during near future (2021-2050) and far future (2070-2099) periods, respectively. However, Liaoning province might have more challenges for premium icewine production under the worst climate warming scenario. Notably, the lower latitude and higher altitude region, Yunnan province, would sustainable provide special premium icewine with a northward expansion of icewine production region to 28.5° N under climate change. The findings provide theoretical support in relieving climate change challenges to premium icewine availability and stability.

Widely targeted metabolomics and SPME-GC-MS analysis revealed the quality characteristics of non-volatile/volatile compounds in Zheng'an Bai tea

Background

As albino tea under the geographical protection of agricultural products, Zheng'an Bai tea is not only rich in amino acids, polyphenols and other beneficial components for the human body, but also its leaf color will turn green as the temperature gradually rises, thus causing changes in the quality characteristics of tea leaves. However, these changing characteristics have not yet been revealed.

Methods

In-depth quality analysis was carried out on the fresh leaves of Zheng'an Bai tea at four different developmental stages and four samples from the processing stage through extensive targeted metabolomics and SPME-GC-MS analysis.

Results

In this study, a total of 573 non-volatile metabolites were detected from the fresh leaves and processing samples of Zheng'an Bai tea, mainly including 96 flavonoids, 75 amino acids, 56 sugars and alcohols, 48 terpenoids, 46 organic acids, 44 alkaloids, and 39 polyphenols and their derivatives. In fresh leaves, the most significant differential metabolites (VIP > 1, p < 0.05) among different samples mainly include substances such as ethyl gallate, theaflavin, isovitexin and linalool, while the main differential metabolites of samples in the processing stage include alkaloids, polyphenols and flavonoids such as zarzissine, methyl L-Pyroglutamate, theaflavin 3,3'-digallate, euscaphic acid and ethyl gallate. Overall, substances such as sugars and alcohols, alkaloids and polyphenols show the greatest differences between fresh leaves and the processing process. Meanwhile, 97 kinds of volatile metabolites were detected in these samples, most of which had a higher content in the fresh leaves. Moderate spreading is conducive to the release of the aroma of tea leaves, but fixation causes a sharp decrease in the content of most volatile metabolites. Ultimately, 9 volatile substances including geraniol, linalool, nerolidol, jasmone, octanal, 1-Nonanal, heptaldehyde, methyl salicylate and 1-Octen-3-ol were identified as the key aroma components (OAV >1) of Zheng'an Bai tea.

Conclusion

In conclusion, this study has for the first time comprehensively revealed the quality change characteristics of fresh leaves at different developmental stages and during the processing of Zheng'an Bai tea, and provided a foundation for further process improvement.

Dynamic changes in the aroma profiles and volatiles of Enshi Yulu tea throughout its industrial processing

Although Enshi Yulu tea (ESYL) possesses a distinctive fragrance, there is a scarcity of studies focusing on its primary volatiles or aroma genesis. This study aims to elucidate the dynamics in the profiles of aromas and volatiles through aroma profiling analysis and headspace solid-phase microextraction/gas chromatography-mass spectrometry. A total of 10 aroma attributes and 128 volatiles were identified in ESYL, with geraniol and linalool exhibiting the highest levels, and alcohols constituting the predominant proportion. Besides, a relative odor activity value (ROAV) based molecular aroma wheel was constructed, revealing 12 key odorants with ROAVs >1, wherein linalool, β-ionone, and nonanal ranked highest. Notably, steaming and final drying emerged as critical steps for ESYL aroma development, while the non-enzymatic degradation of fatty acids likely contributed to the formation of its fresh aroma. These findings significantly enhance our comprehension of ESYL aroma formation.

Investigation of non-volatile metabolite variations during round green tea processing and effect of pan-frying degree using untargeted metabolomics and objective quantification

Round green tea (RGT) presents unique properties and is widely distributed in China, and during processing, it undergoes dynamic changes in non-volatile metabolites (NVMs), which are poorly understood. Utilizing UHPLC-Q-Exactive/MS analysis, this study comprehensively characterized 216 NVMs during RGT processing and identified fixation and pan-frying as key processes influencing NVMs. Additionally, 23 key differential NVMs were screened, with amino acid and flavonoid metabolism highlighted as key metabolic pathways for RGT taste and color quality. The impact of pan-frying degree on shape, color, and taste was also explored. Moderate pan-frying led to optimal results, including a tight and round shape, green and bright color, mellow and umami taste, and reduced astringent and bitter taste NVMs, including epigallocatechin gallate, procyanidin B2, myricetin 3-O-galactoside, quinic acid, strictinin, phenylalanine, and theobromine. This study addresses the NVM research gap in RGT processing, thus providing a technical foundation for the precision-oriented processing of high-quality tea.

Revealing the differences in aroma of black tea under different drying methods based on GC-MS, GC-O

Drying greatly affects the aroma of black tea. In this study, the differences in aroma of black tea under hot-air drying (HD), sun drying (SD), and pan-fired drying (PD) were investigated through quantitative descriptive analysis. Headspace solid-phase microextraction and solvent assisted flavor evaporation combined with gas chromatography-mass spectrometry and gas chromatography-olfactory were used to analyze the overall aroma profile of black tea. Aroma extract dilution analysis and odor activity values revealed that 15 aroma-active compounds led to differences in aroma, namely linalool, geraniol, phenylethyl alcohol, phenylacetaldehyde, (Z) -linalool oxide (furanoid), β-damascenone, dimethyl sulfide, methional, 2-methylbutanal, 3-methylbutanal, methyl salicylate, β-myrcene, hexanal, 1-octen-3-ol, and heptanal. Among them, geraniol, linalool, and methional significantly enhanced the floral and roasty aroma of HD, while hexanal enhanced the green aroma of SD. Finally, our results were validated through aroma recombination and addition experiments. This study provides a theoretical basis for improving the aroma of black tea.

Dynamic changes and interaction between different aroma types during low-temperature roasting of bud green tea

As an important process for enhancing aroma of Wuyi rock tea, roasting has gradually been applied to the processing of bud green tea (BGT). However, there is a lack of comprehensive research on the impact of roasting on BGT aroma. This research provides a detailed analysis of the changes in aroma perception and compounds during the low-temperature roasting process (105°C, 90 minutes) of BGT. First, the changes in aroma perception were studied using quantitative descriptive analysis (QDA). The aroma perception of BGT transformed from fresh to chestnut like. Next, headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) analysis was conducted to characterize the volatile compounds during roasting. A total of 313 volatile compounds were identified, among which 72 showed significant differences. Compounds such as linalool, benzyl alcohol, ionone, and ethyl salicylate (floral aroma) and 2,6-dimethylpyrazine, 2,3-dimethylpyrazine, 2-acetylpyrrole, and 3-furfural (caramel-like aroma) were confirmed to be involved in the formation of the chestnut-like aroma during roasting process. In addition, representative aroma compounds with different characteristics were selected based on monomolecular olfactory results to simulate sensory-level aroma interactions. The results showed that fresh and tender aromas exhibited mutual enhancement at low concentrations, while sweet and chestnut-like aromas showed mutual enhancement at all concentrations.

Extensive ICP-MS and HPLC-QQQ detections reveal the content characteristics of main metallic elements and polyphenols in the representative commercial tea on the market

The content of polyphenols and metal elements in tea has an important impact on the choice of consumers. In this study, we conducted a comparative analysis of ten elements including Fe, Mg, Al, Zn, Cu, Mn, Ni, Cr, Pb, and As in 122 representative tea samples from 20 provinces. The results showed that the difference of metal content among six tea categories was greater than that among provinces, and the overall metal content of black tea was relatively higher. The contents of all elements from high to low were: Mg > Mn > Al > Fe > Zn > Cu > Ni > Cr > Pb > As. The contents of Ni, Fe, Al, Zn and Mn showed significant differences among multiple types of tea categories. While the detection rates of Pb and As were 10.7 and 24.6%, respectively. The contents of all elements were in line with the national limit standards. Meanwhile, the relative contents of theanine, caffeine and a total of 53 polyphenolic compounds in 122 tea samples were detected. The analysis showed that the content of these compounds differed least between green and yellow tea, and the largest difference between black tea and oolong tea. This study provides important support for consumers to choose tea rationally.

Effects of processing methods on the aroma of Poria cocos and its changing regulations during processing

Poria cocos is a natural source of fungal food raw materials. Processing method is a key effecting the aroma of Poria cocos. In this study, the aroma compounds of Poria cocos products processed using sweating-low-temperature drying (SW-LD), sweating-high-temperature drying (SW-HD), steaming-low-temperature drying (ST-LD), and steaming-high-temperature drying (ST-HD) were compared by headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS), and the changes in aroma compounds of Poria cocos products during processing were analyzed. GC-MS analysis showed SW-HD product had highest content of aroma compounds. Aroma activity value (OAV) analysis indicated that 9 aroma compounds contributed to the overall aroma of Poria cocos. Among 9 compounds of Poria cocos, 1-octen-3-ol, hexanal, nonanal, octanal, trans-2-octenal, and heptanal contributed to mushroom, refreshing, sweet and fatty characters. In addition, the aroma compound changes during the processing were analyzed, revealing that steaming and sweating were the key processes affecting the aroma of Poria cocos products. The findings of this study provide valuable theoretical guidance for the development of Poria cocos processing technology.

The Light-Intensity-Affected Aroma Components of Green Tea during Leaf Spreading

Leaf spreading is a key processing step that affects the aroma formation of green tea. The effects of a single-light wavelength on the aroma and taste of tea have been extensively studied. Less attention has been paid to the effect of different complex light intensities on the formation of green tea's volatile aroma during leaf spreading. The current study was designed to evaluate how leaf spreading under different complex light intensities relates to the quality of green tea. Using headspace solid-phase micro-extraction and gas chromatography-mass spectrometry (HS-SPME/GC-MS), volatile flavor compounds in green tea were analyzed during leaf spreading in five different light conditions. Multivariate statistical analysis and odor activity values (OAVs) were used to classify these samples and identify key odors. Eight distinct groups, including ninety volatile compounds, were detected. The most prevalent volatile compounds found in green tea samples were hydrocarbons and alcohols, which accounted for 29% and 22% of the total volatile compounds, respectively. Fourteen volatile compounds (OAV > 1) were identified as key active differential odorants. The chestnut-like aroma in green tea was mostly derived from 3-methyl-butanal and linalool, which were significantly accumulated in medium-intensity light (ML).

Comprehensive Analysis of the Yield and Leaf Quality of Fresh Tea (Camellia sinensis cv. Jin Xuan) under Different Nitrogen Fertilization Levels

Reasonable application of nitrogen fertilizer can improve the yield and quality of tea. This study used Jin Xuan as the tested variety and applied nitrogen fertilizer at rates of 0 kg/ha (N0), 150 kg/ha (N150), 300 kg/ha (N300), and 450 kg/ha (N450) in the summer and autumn seasons to analyze the effects of nitrogen application on the quality components and gene expression of tea leaves. The results showed that the N150 treatment significantly increased total polyphenols (TP), total catechins (TC), and caffeine contents, with the most significant increase observed in the content of six monomers of catechins (EGCG, ECG, EGC, GCG, GC, and EC) in the summer. The N300 treatment significantly increased TP and AA contents in the autumn while decreasing TC content. Additionally, the N300 treatment significantly increased caffeine and theanine contents in the autumn. Notably, the N300 treatment significantly increased both summer and autumn tea yields. Multivariate statistical analysis showed that TPs, AAs, TCs, EGC, and caffeine were key factors affecting the quality of Jin Xuan. Furthermore, the N150 treatment upregulated the expression of the phenylalanine ammonia-lyase (PAL) gene, which may increase the accumulation of catechins. In conclusion, it is recommended to apply 150 kg/ha of nitrogen fertilizer in the summer and 300 kg/ha of nitrogen fertilizer in the autumn. This recommendation provides a theoretical basis for improving the quality and yield of tea leaves in summer and autumn.

Combined multi-omics approach to analyze the flavor characteristics and formation mechanism of gabaron green tea

Gabaron green tea (GAGT) has unique flavor and health benefits through the special anaerobic treatment. However, how this composite processing affects the aroma formation of GAGT and the regulatory mechanism was rarely reported. This study used nontargeted metabolomics and molecular sensory science to overlay screen differential metabolites and key aroma contributors. The potential regulatory mechanism of anaerobic treatment on the aroma formation of GAGT was investigated by transcriptomics and correlation analyses. Five volatiles: benzeneacetaldehyde, nonanal, geraniol, linalool, and linalool oxide III, were screened as target metabolites. Through the transcriptional-level differential genes screening and analysis, some CsERF transcription factors in the ethylene signaling pathway were proposed might participate the response to the anaerobic treatment. They might regulate the expression of related genes in the metabolic pathway of the target metabolites thus affecting the GAGT flavor. The findings of this study provide novel information on the flavor and its formation of GAGT.

The enhancement of flowery-like aroma in green tea under optimized processing conditions by sensory-directed flavor analysis

Flowery-like aroma are positive contributors to green tea. Here, the optimal processing conditions for green tea with flowery-like aroma were designed using spreading time, fixation time and drying temperature as three factors designed by response surface methodology (RSM), and the response value of aroma sensory evaluation score. The volatiles in batches of tea samples were analyzed by GC-MS. The optimal quality was obtained with a flowery-like aroma by RSM under a spreading time of 8.97 h, fixation time of 162.3 s, and drying temperature of 103.32 °C. GC-O and odor activity values further revealed floral-like volatiles, including decanal, linalool oxide, β-lonone, geraniol, (Z)-jasmone, linalool, nonanal, and benzeneacetaldehyde. The recombination of these floral volatiles confirmed the consistency with the floral green tea. Furthermore, the extending spreading duration (8-10 h), reducing fixation duration (160-190 s), and increasing drying temperature (100-115 °C) promote their accumulation in green tea. This study provides new perspectives for the precise enhancement of floral odorants for green tea.

Study on flavor quality formation in green and yellow tea processing by means of UPLC-MS approach

Yellow tea (YT) has an additional process of yellowing before or after rolling than green tea (GT), making YT sweeter. We analyzed the variations of composition and taste throughout the withering, fixing and rolling steps using UPLC-MS/MS and sensory evaluation, and investigated the influence of various yellowing times on flavor profile of YT. 532 non-volatile metabolites were identified. Withering and fixing were the important processes to form the taste quality of GT. Withering, fixing and yellowing were important processes to form flavor profile of YT. Withering mainly regulated bitterness and astringency, and fixing mainly regulated bitterness, astringency and sweetness of YT and GT. Yellowing mainly regulated sweetness of YT. Trans-4-hydroxy-L-proline and glutathione reduced form as the key characteristic components of YT, increased significantly during yellowing mainly through Arginine and proline metabolism and ABC transporters. The paper offers a systematic insight into intrinsic mechanisms of flavor formation in YT and GT.

Effects of processing technology on tea quality analyzed using high-resolution mass spectrometry-based metabolomics

Fixation is a crucial step in green tea processing that can impact quality. In this study, we explored the differences in the chemical components of steamed and fried green teas made from the same batch of fresh tea leaves using different fixing methods. Results showed that concentrations of sucrose and free amino acids were significantly higher in steamed green tea. Abundances of 12 compounds including purine nucleoside, pyrimidine nucleoside derivatives, and catechins were higher in fried green tea, while 34 compounds such as amino acids and their derivatives, benzofurans and flavonoids were higher in steamed green tea. Thus, steaming retained more compounds associated with sweet and fresh tastes, such as free amino acids, while frying produced more compounds with bitter tastes, such as catechin. This might explain why steamed green tea is mellower than fried tea.

GC-MS Combined with Proteomic Analysis of Volatile Compounds and Formation Mechanisms in Green Teas with Different Aroma Types

Aroma is one of the key factors for evaluating the quality of green tea. A tender aroma (NX) and floral-like aroma (HX) are two types of high-quality aroma of green tea. In this work, the different aroma types of baked green tea were classified by sensory evaluation. Then, seven tea samples with a typical tender or floral-like aroma were selected for further volatile component analysis by GC-MS. A total of 43 aroma compounds were identified in two different aroma types of baked green tea samples. The PCA showed that linalool, geraniol, 3-hexenyl butyrate, and 3-hexenyl hexanoate were the major volatiles contributing to the HX. On the other hand, most of the alcohol volatiles, such as 1-octanol, 1-octen-3-ol, 1-dodecanol, 1-hexadecanol, phenylethyl alcohol, benzyl alcohol, aldehydes and some hydrocarbons contributed more to the NX. In addition, the chemical composition analysis showed that the content of free amino acids was higher in NX green tea samples, while the content of catechins was relatively higher in HX tea samples. A proteomic analysis revealed that most of the enzymes involved in VPBs pathways, such as phenylalanine ammonialyase, peroxidase, and shikimate-O-hydroxycinnamoyl transferase, were more abundant in NX than in HX tea samples. These results laid a foundation for the aroma formation mechanism of different aroma types of baked green tea and provided some theoretical guidance for the breeding of specific aroma varieties.

Metabolite Profiling Reveals the Dynamic Changes in Non-Volatiles and Volatiles during the Enzymatic-Catalyzed Processing of Aijiao Oolong Tea

The enzymatic reaction stage (ECS) of oolong tea processing plays an important role in the formation of the flavor quality of the oolong tea. To investigate the dynamic changes in the volatile and non-volatile components in the leaves of oolong tea during the ECS, metabolomic studies were carried out using the leaf samples collected at different stages of the ECS of Aijiao oolong tea. Out of the identified 306 non-volatile metabolites and 85 volatile metabolites, 159 non-volatile metabolites and 42 volatile metabolites were screened out as key differential metabolites for dynamic changes during the ECS. A multivariate statistical analysis on the key differential metabolites showed that the accumulations of most metabolites exhibited dynamic changes, while some amino acids, nucleosides, and organic acids accumulated significantly after turning-over treatment. The evolution characteristics of 27 key precursors or transformed VOCs during the ECS of Aijiao oolong tea were clarified, and it was found that the synthesis of aroma substances was mainly concentrated in lipids as precursors and glycosides as precursor pathways. The results revealed the dynamic changes in the flavor metabolites in the ECS during the processing of Aijiao oolong tea, which provided valuable information for the formation of the characteristic flavor of Aijiao oolong tea.

Research of Processing Technology of Longjing Tea with 'Baiye 1' Based on Non-Targeted Aroma Metabolomics

Longjing tea is favored by consumers due to its refreshing and delicate aroma, as well as its fresh and sweet flavor. In order to study the processing technology of Longjing tea with 'Baiye 1' tea varieties, solid phase microextraction and gas chromatography-mass spectrometry were used to analyze the volatile components of Longjing tea in different process stages. The results revealed the identification of 275 aroma metabolites in the processing samples of Longjing tea. The sensory evaluation and principal component analysis revealed that the leaves of fresh (XY) and spreading (TF) were different from the leaves of first panning (YQ), second panning (EQ), final panning (HG), and fragrance enhancing (TX). The relative contents of geraniol (1199.95 and 1134.51), linalool (745.93 and 793.98), methyl salicylate (485.22 and 314.67), phenylethyl alcohol (280.14 and 393.98), 2-methylfuran (872.28 and 517.96), 2-butenal (56.01 and 154.60), and 2-hexenal (46.22 and 42.24), refreshing and floral substances in the XY and TF stages, were higher than other stages. The aroma contents of 2-methylfuran, furfural, 2-methyl-1-penten-3-one, 3-hexen-2-one, dodecane, hexanoyl hexanoate, 2,5-dimethyl-pyrazine, and methyl-pyrazine were found to be significantly positively correlated with the intensity of chestnut aroma. In conclusion, this study contributes to a better understanding of the composition and formation mechanism of chestnut-like aroma and provides new insights into the processing technology to improve the quality of albino green tea.

Insights into the effects of fixation methods on the sensory quality of straight-shaped green tea and dynamic changes of key taste metabolites by widely targeted metabolomic analysis

Fresh leaves of Echa 1 were fixed by roller, steam/hot air and light-wave, and the effects of the three fixation methods on the chemical characteristics of straight-shaped green teas (GTs) were studied by widely targeted metabolomic analysis. 1001 non-volatile substances was identified, from which 97 differential metabolites were selected by the criteria of variable importance in projection (VIP) > 1, p < 0.05, and |log2(fold change)| > 1. Correlation analysis indicated that 14 taste-active metabolites were the major contributors to the taste differences between differently processed GTs. High-temperature fixation induces protein oxidation or degradation, γ-glutamyl peptide transpeptidation, degradation of flavonoid glycosides and epimerization of cis-catechins, resulting in the accumulation of amino acids, peptides, flavonoids and trans-catechins, which have flavor characteristics such as umami, sweetness, kokumi, bitterness and astringency, thereby affecting the overall taste of GTs. These findings provided a scientific basis for the directional processing technology of high-quality green tea.

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

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

Insights into momentous aroma dominating the characteristic flavor of jasmine tea

Jasmine tea is loved by most people who drink flower tea owing to its unique aroma, and it is known as the top of flower teas. In our study, the quantitative evaluation of the quality of jasmine tea and detection of aroma components were carried out. First, the flavor quality of 92 kinds of jasmine tea was evaluated using multiple sub-factor quality evaluation methods. According to the evaluation results, jasmine tea was divided into three types: "fresh and lovely" (FL), "heavy and thick" (HT), and "fresh and heavy" (FH). Gas chromatography-mass spectrometry (GC-MS) was used to detect the aroma components of the three types of jasmine tea samples. α-Farnesene, cis-3-hexenyl benzoate, acid phenylmethyl ester, linalool, methyl anthranilate, and indole were the main substances that constituted the basic aroma quality characteristics of jasmine tea. Compared to the FL type, the HT and FH types were weaker in the diversification of the characteristic aroma and accumulation of green, herb, sweet, and roast aroma substances. Green and herb aromas play crucial roles in the fresh and persistent qualities of the three types of jasmine tea, which are the key quality factors research focus of jasmine tea.

Characterization of key volatile compounds in jasmine tea infusion with different amount of flowers

The quality of jasmine tea is related to the volatiles of its infusion. In this study, the volatiles of jasmine tea infusion were extracted under the optimal conditions with a 50/30 μm DVB/CAR/PDMS fiber, tea/water ratio of 1:25 and extraction time of 5 min. A total of 204 volatiles were analyzed by comprehensive two-dimensional gas chromatography-quadrupole time-of-flight mass spectrometry (GC × GC-Q-TOF-MS). Twenty-five compounds were identified as the key volatile compounds by fold change (FC), orthogonal partial least squares discriminant analysis (OPLS-DA), and two-way orthogonal partial least squares analysis (O2PLS). Then optimal amount of flowers (80%-120%) was obtained by the equation describing key volatiles and quality of jasmine tea infusion. And 80% amount of flowers was more appropriate considering the production cost and more pleasant taste. This study laid a foundation for the extraction and research of volatiles of tea infusion and guided the reasonable amount of flowers to produce jasmine tea.

Effects of electromagnetic roller-hot-air-steam triple-coupled fixation on reducing the bitterness and astringency and improving the flavor quality of green tea

Despite the importance of fixation in determining green tea quality, its role in reducing the bitter and astringent taste of this beverage remains largely unknown. Herein, an electromagnetic roller-hot-air-steam triple-coupled fixation (ERHSF) device was developed, and its operating parameters were optimized (steam volume: 20 kg/h; hot-air temperature: 90 °C; hot-air blower speed: 1200 r/min). Compared with conventional fixation treated samples, the ratio of tea polyphenols to free amino acids and ester-catechins to simple-catechins in ERHSF-treated samples was reduced by 11.0% and 3.2%, reducing bitterness and astringency of green tea; amino acids, soluble sugars, and chlorophyll contents were significantly increased, enhancing the freshness, sweetness, and greenness; the color indexes, such as L/L* value of brightness and -a/-a* value of greenness, were also improved, and ERHSF-treated samples had the highest sensory scores. These results provided theoretical support and technical guidance for precise quality improvement of summer-autumn green tea.

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

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

Decoding the Chemical Signatures and Sensory Profiles of Enshi Yulu: Insights from Diverse Tea Cultivars

Enshi Yulu, a renowned Chinese steamed green tea, is highly valued for its unique sensory attributes. To enhance our comprehensive understanding of the metabolic variation induced by steaming fixation, we investigated the overall chemical profiles and organoleptic quality of Enshi Yulu from different tea cultivars (Longjing 43, Xiapu Chunbolv, and Zhongcha 108). The relationships between sensory traits and non-volatiles/volatiles were evaluated. A total of 58 volatiles and 18 non-volatiles were identified as characteristic compounds for discriminating among the three tea cultivars, and the majority were correlated with sensory attributes. The "mellow" taste was associated with L-aspartic acid, L-asparagine, L-tyrosine, L-valine, EGC, EC, and ECG, while gallic acid and theobromine contributed to the "astringent" taste. "Kokumi" contributors were identified as L-methionine, L-lysine, and GCG. Enshi Yulu displayed a "pure" and "clean and refreshing" aroma associated with similar volatiles like benzyl alcohol, δ-cadinene, and muurolol. The composition of volatile compounds related to the "chestnut" flavor was complex, including aromatic heterocycles, acids, ketones, terpenes, and terpene derivatives. The key contributors to the "fresh" flavor were identified as linalool oxides. This study provides valuable insights into the sensory-related chemical profiles of Enshi Yulu, offering essential information for flavor and quality identification of Enshi Yulu.

Analysis of Volatile Components in Dried Fruits and Branch Exudates of Schisandra chinensis with Different Fruit Colors Using GC-IMS Technology

To investigate the volatile components of Schisandra chinensis (Turcz.) Bail (commonly known as northern Schisandra) of different colors and to explore their similarities and differences, to identify the main flavor substances in the volatile components of the branch exudates of northern schisandra, and finally to establish a fingerprint map of the volatile components of the dried fruits and branch exudates of northern Schisandra of different colors, we used GC-IMS technology to analyze the volatile components of the dried fruits and branch exudates of three different colors of northern Schisandra and established a fingerprint spectra. The results showed that a total of 60 different volatile chemical components were identified in the branch exudates and dried fruits of Schisandra. The components of germplasm resources with different fruit colors were significantly different. The ion mobility spectrum and OPLS-DA results showed that white and yellow fruits were more similar compared to red fruits. The volatile components in dried fruits were significantly higher than those in branch exudates. After VIP (variable importance in projection) screening, 41 key volatile substances in dried fruits and 30 key volatile substances in branch exudates were obtained. After screening by odor activity value (OAV), there were 24 volatile components greater than 1 in both dried fruits and branch exudates. The most important contributing volatile substance was 3-methyl-butanal, and the most important contributing volatile substance in white fruit was (E)-2-hexenal.

Effects of processing methods on quality, antioxidant capacity, and cytotoxicity of Ginkgo biloba leaf tea product

BACKGROUND

Ginkgo biloba leaves contain beneficial flavonoids, bilobalide (BB), and ginkgolides. However, the toxic ginkgolic acid (GA) limit its application. In this study, various traditional processing methods were used to prepare G. biloba leaf tea (GBLT), including white tea, black tea, dark tea, green tea, and freeze-dried as control, followed by investigations of their effects on quality, antioxidant capacity, bioactive components, and cytotoxicity of the tea products.

RESULTS

Results showed that different processing methods significantly impact the tea products' quality indexes and the principal component analysis (PCA) and hierarchical cluster analysis (HCA) corroborated it. White tea had the highest total sugar (TS) and GA content and the most potent cytotoxicity on HepG2 cells. However, TS and GA content and the cytotoxicity of GBLT markedly decreased during fermentation and fixation. Moreover, white tea possessed higher total phenolic content (TPC), total flavonoid content (TFC), and more vigorous antioxidant activities than green tea, black tea, and dark tea. Terpene trilactones value was stable, but different catechins contents fluctuated according to the manufacturing process of different GBLTs. Among the four GBLTs, dark tea combining fixation and fermentation had the lowest GA content and cytotoxicity, less bioactive components reduction, appropriate quality, and stronger flavor.

CONCLUSION

These findings demonstrate that fixation and fermentation help reduce GAs during the manufacturing of GBLT. However, their ability to retain bioactive substances needs further optimization in future studies. © 2023 Society of Chemical Industry.

Study on taste quality formation and leaf conducting tissue changes in six types of tea during their manufacturing processes

This study fristly investigated the taste quality formation and leaf conducting tissue changes in six types of Chinese tea (green, black, oolong, yellow, white, and dark) made from Mingke No.1 variety. Non-targeted metabolomics showed the vital manufacturing processes (green tea-de-enzyming, black tea-fermenting, oolong tea-turning-over, yellow tea-yellowing, white tea-withering, and dark tea-pile-fermenting) were highly related to their unique taste formation, due to different fermentation degree in these processes. After drying, the retained phenolics, theanine, caffeine, and other substances significantly impacted each tea taste quality formation. Meanwhile, the tea leaf conducting tissue structure was significantly influenced by high processing temperature, and the change of its inner diameter was related to moisture loss during tea processing, as indicated by its significant different Raman characteristic peaks (mainly cellulose and lignin) in each key process. This study provides a reference for process optimization to improve tea quality.

Effects of Sun Withering Degree on Black Tea Quality Revealed via Non-Targeted Metabolomics

In this study, the effects of different sun withering degrees (75% (CK), 69% (S69), 66% (S66), 63% (S63), and 60% (S60) water content in the withered leaves) on black tea sensory quality were investigated by means of sensory evaluation plus metabolomics analysis. Sensory evaluation results showed higher sensory quality scores for the black tea in S69-S66, due to better freshness, sweeter taste, and a sweet and even floral and fruity aroma. Additionally, 65 non-volatile components were identified using Ultra Performance Liquid Chromatography-Quadrupole-Time of Flight-Mass Spectrometry (UPLC-Q-TOF/MS). Among them, the content increase of amino acids and theaflavins was found to promote the freshness and sweetness of black tea. The aroma of tea was analyzed using combined Solvent Assisted Flavor Evaporation-Gas Chromatography-Mass Spectrometry (SAFE-GC-MS) and Headspace-Solid Phase Micro Extract-Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS), and 180 volatiles were identified, including 38 variable importance in projection (VIP) > 1 (p < 0.05) and 25 Odor Activity Value (OAV) > 1 volatiles. Statistical analysis revealed 11 volatiles as potential major aroma differential metabolites in black tea with a different sun withering degree, such as volatile terpenoids (linalool, geraniol, (E)-citral, and β-myrcene), amino-acid-derived volatiles (benzeneethanol, benzeneacetaldehyde, and methyl salicylate), carotenoid-derived volatiles (jasmone and β-damascenone), and fatty-acid-derived volatiles ((Z)-3-hexen-1-ol and (E)-2-hexenal). Among them, volatile terpenoids and amino acid derived volatiles mainly contributed to the floral and fruity aroma quality of sun-withered black tea.

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

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

A comprehensive review of polyphenol oxidase in tea (Camellia sinensis): Physiological characteristics, oxidation manufacturing, and biosynthesis of functional constituents

Polyphenol oxidase (PPO) is a metalloenzyme with a type III copper core that is abundant in nature. As one of the most essential enzymes in the tea plant (Camellia sinensis), the further regulation of PPO is critical for enhancing defensive responses, cultivating high-quality germplasm resources of tea plants, and producing tea products that are both functional and sensory qualities. Due to their physiological and pharmacological values, the constituents from the oxidative polymerization of PPO in tea manufacturing may serve as functional foods to prevent and treat chronic non-communicable diseases. However, current knowledge of the utilization of PPO in the tea industry is only available from scattered sources, and a more comprehensive study is required to reveal the relationship between PPO and tea obviously. A more comprehensive review of the role of PPO in tea was reported for the first time, as its classification, catalytic mechanism, and utilization in modulating tea flavors, compositions, and nutrition, along with the relationships between PPO-mediated enzymatic reactions and the formation of functional constituents in tea, and the techniques for the modification and application of PPO based on modern enzymology and synthetic biology are summarized and suggested in this article.

Analyzing the influence of withering degree on the dynamic changes in non-volatile metabolites and sensory quality of Longjing green tea by non-targeted metabolomics

Withering is an important processing stage in green tea, which contributes to the tea flavor quality. The aim of this work was to comprehensively investigate the changes of chemical features and flavor attributes in Longjing green teas produced with five different withering degrees (moisture content of 75.05, 72.53, 70.07, 68.00, and 64.78%, w.b.). Combined with human sensory evaluation, electronic tongue and chromatic differences analysis, an assessment of the relationship between the withering degree and the sensory quality of Longjing tea was obtained. By using a non-targeted metabolomics approach, 69 significantly differential metabolites were screened. As the withering degree increased, most free amino acids and catechin dimers were increased, largely attributed to the hydrolysis of proteins and catechin oxidative polymerization, respectively. The contents of organic acids as well as phenolic acids and derivatives were reduced. Interestingly, flavone C-glycosides decreased overall while flavonol O-glycosides increased. The correlation analysis revealed that metabolites such as theasinensin F, theasinensin B, theaflavin, theaflavin-3,3′-gallate, theaflavin-3′-gallate, malic acid, succinic acid, quinic acid, theanine glucoside and galloylglucose had a greater influence on the taste and color of tea infusion (|r| &gt; 0.6, p &lt; 0.05). Overall, an appropriate withering degree at a moisture content of around 70% is more favorable to enhance the Longjing tea quality. These results may enhance the understanding of green tea flavor chemistry associated with withering and provide a theoretical basis for green tea processing.

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

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

Effects of leaf-spreading on the volatile aroma components of green tea under red light of different intensities

Spreading is an indispensable process in the aroma formation of green tea. The application of exogenous red-light spreading in tea processing has been verified to significantly improve the aroma of green tea, and endow tea with freshness, sweet flavor, and mellow taste. However, there were no previous studies investigating the effects of spreading with different red-light intensities on the aroma components of green tea. The aim of the present study was to evaluate the effect of the relationship between the aroma component and spreading with different red-light intensities (300 μmol∙m^-2∙s^-1, 150 μmol∙m^-2∙s^-1 and 75 μmol∙m^-2∙s^-1). As a result, a total of ninety-one volatile components were identified in this study. The orthogonal partial least squares discriminant analysis (OPLS-DA) model clearly distinguished the volatile components of green tea between different red-light intensities and obtained thirty-three differential volatile compounds. Combined with odor activity value (OAV > 1) analysis revealed that eleven volatile components were the key volatile compounds of green tea under different light conditions. Among them, 3-methyl-butanal, (E)-nerolidol, and linalool were the sources of chestnut-like aroma in green tea and were significantly accumulated under medium (MRL) and low intensity (LRL) red light. The results of the present study provided a theoretical basis that could guide green tea processing with red-light intensities to increase the aroma quality components of green tea.

Characterization of volatile organic compounds with anti-atherosclerosis effects in Allium macrostemon Bge. and Allium chinense G. Don by head space solid phase microextraction coupled with gas chromatography tandem mass spectrometry

Introduction

Allium macrostemon Bge. (AMB) and Allium chinense G. Don (ACGD) are both edible Allium vegetables and named officinal Xiebai (or Allii Macrostemonis Bulbus) in East Asia. Their medicinal qualities involve in lipid lowering and anti-atherosclerosis effects. And steroidal saponins, nitrogenous compounds and sulfur compounds are like the beneficial components responsible for medicinal functions. Sulfur compounds are the recognized main components both in the volatile oils of AMB and ACGD. Besides, few researches were reported about their holistic chemical profiles of volatile organic compounds (VOCs) and pharmacodynamic effects.

Methods

In this study, we first investigated the lipid-lowering and anti-atherosclerotic effects of volatile oils derived from AMB and ACGD in ApoE ^-/- mice with high fat and high cholesterol diets.

Results

The results showed the volatile oils of AMB and ACGD both could markedly reduce serum levels of TG, TC, and LDL-C (p < 0.05), and had no alterations of HDL-C, ALT, and AST levels (p > 0.05). Pathological results displayed they both could obviously improve the morphology of cardiomyocytes and the degree of myocardial fibrosis in model mice. Meanwhile, oil red O staining results also proved they could apparently decrease the lesion areas of plaques in the aortic intima (p < 0.05). Furthermore, head space solid phase microextraction coupled with gas chromatography tandem mass spectrometry combined with metabolomics analysis was performed to characterize the VOCs profiles of AMB and ACGD, and screen their differential VOCs. A total of 121 and 115 VOCs were identified or tentatively characterized in the volatile oils of AMB and ACGD, respectively. Relative-quantification results also confirmed sulfur compounds, aldehydes, and heterocyclic compounds accounted for about 85.6% in AMB bulbs, while approximately 86.6% in ACGD bulbs were attributed to sulfur compounds, ketones, and heterocyclic compounds. Multivariate statistical analysis showed 62 differentially expressed VOCs were observed between AMB and ACGD, of which 17 sulfur compounds were found to be closely associated with the garlic flavor and efficacy.

Discussion

Taken together, this study was the first analysis of holistic chemical profiles and anti-atherosclerosis effects of AMB and ACGD volatile oils, and would benefit the understanding of effective components in AMB and ACGD.

Effect of thermal process on the key aroma components of green tea with chestnut-like aroma

BACKGROUND

Chestnut-like aroma is one of the unique qualities of Chinese green tea and has become an important factor influencing consumer decisions. However, the chemical formation mechanism of chestnut-like aroma during green tea processing remains unclear. In this study, the dynamic changes of key components contributing to chestnut-like aroma and their precursors were analyzed in fresh leaves, fixation leaves, first baking tea leaves, and green tea.

RESULTS

The thermal process had an important effect on volatile components in tea leaves, causing a significant decrease of alcohols and esters and a significant increase of ketones, acids, phenols, and sulfur compounds. Furthermore, 31 volatiles were identified as the key odorants responsible for chestnut-like aroma of green tea, including dimethyl sulfide, methyl isobutenyl ketone, 2-methylbutanal, 2,4-dimethylstyrene, d-limonene, methyl 2-methylvalerate, linalool, decanal, longifolene, phenylethyl alcohol, l-α-terpineol, jasmone, and so on. And the majority of these odorants were only formed in the drying stage. Additionally, isoleucine, theanine, methionine, and glucose were found to be involved in the formation of chestnut-like aroma of green tea.

CONCLUSION

The drying process played a vital important role in the formation of chestnut-like aroma of green tea. © 2022 Society of Chemical Industry.

The New Insight into the Effects of Different Fixing Technology on Flavor and Bioactivities of Orange Dark Tea

Peach leaf orange dark tea (ODT) is a fruity tea made by removing the pulp from peach leaf orange and placing dry Qingzhuan tea into the husk, followed by fixing them together and drying. Since the quality of traditional outdoor sunlight fixing (SL) is affected by weather instability, this study explored the feasibility of two new fixing methods, including hot air fixing (HA) and steam fixing (ST). Results showed that fixing method had a great impact on ODT shape, aroma, and taste. Compared with SL and ST, HA endowed ODT with higher fruit aroma, mellow taste, better coordination, and higher sensory evaluation score. Physical-chemical composition analysis showed that SL-fixed orange peel was higher than HA- or ST-fixed peel in the content of polyphenols, flavonoids, soluble protein, hesperidin and limonin, while HA has a higher content of volatile substances and contains more alcohols, aldehydes and ketones, and acid and esters than ST and SL. Activity analysis showed that HA was superior to ST or SL in comprehensive antioxidant activity and inhibitory activity against α-glucosidase. Comprehensive results demonstrated that HA has better performance in improving ODT quality and can replace the traditional SL method in production.

Effects of Maturity and Processing on the Volatile Components, Phytochemical Profiles and Antioxidant Activity of Lotus (Nelumbo nucifera) Leaf

In this study, fresh lotus leaves at two maturity stages were processed to tea products by different methods (white-tea process, green-tea process and black-tea process). The volatile compounds, phytochemical profiles and antioxidant activities of lotus-leaf tea were investigated. A total of 81 volatile components were identified with HS-GC-IMS. The mature lotus-leaf tea showed more volatile compounds than the tender lotus-leaf tea. The lotus leaf treated with the white-tea process had more aroma components than other processing methods. In addition, six types of phenolic compounds, including luteolin, catechin, quercetin, orientin, hyperoside and rutin were identified in the lotus-leaf tea. The mature leaves treated with the green-tea process had the highest levels of TPC (49.97 mg gallic acid/g tea) and TFC (73.43 mg rutin/g tea). The aqueous extract of lotus-leaf tea showed positive scavenging capacities of DPPH and ABTS radicals, and ferric ion reducing power, whereas tender lotus leaf treated with the green-tea process exhibited the strongest antioxidant activity. What is more, the antioxidant activities had a significant positive correlation with the levels of TPC and TFC in lotus-leaf tea. Our results provide a theoretical basis for the manufacture of lotus-leaf-tea products with desirable flavor and health benefits.

The Effects of Fixation Methods on the Composition and Activity of Sea Buckthorn (Hippophae rhamnoides L.) Leaf Tea

Fixation is the key step to improve the quality of sea buckthorn leaf tea. Composition and activity are important indexes to evaluate the quality of sea buckthorn leaf tea. Comparing the effects of fixation methods on components and activities provides a theoretical basis for the contemporary, controllable, and continuous production of sea buckthorn leaf tea. The effects of six different fixed methods, pan-firing fixed (PF), steaming fixed (SF), boiling water fixed (BF), hot air fixed (HF), microwave fixed (MWF), and infrared fixed (IRF) for sea buckthorn leaf tea in terms of α-glucosidase inhibitory activity, lipase inhibitory ability, and the antioxidant capacity were studied. The total flavonoids (TF) content, total soluble phenolics (TP) content, water-soluble carbohydrate (WSC) content, the inhibitory activity of α-glucosidase, lipase inhibitory ability, and the antioxidant capacity of fixed sea buckthorn leaf tea were significantly higher ( $p\le 0.05$ ) compared with sea buckthorn leaf. IRF and MWF samples had higher ( $p\le 0.05$ ) contents of TF (92.48 mg RE/g and 79.20 mg RE/g), TP (115.37 mg GA/g and 135.18 mg GA/g) and WSC (4.24% and 4.39%). The DPPH radical scavenging activity of the SF sample was the strongest one, followed by the MWF sample and IRF sample ( $p\le 0.05$ ). The hydroxyl radical scavenging ability and reducing power of IRF were the strongest one, followed by the MWF sample ( $p\le 0.05$ ). The IRF sample had the strongest α-glucosidase inhibitory activity ( $p\le 0.05$ ), and the MWF sample had the strongest lipase inhibitory ability while samples contained the same amount of total polyphenols ( $p\le 0.05$ ). Principal component analysis results showed that the IRF sample, MWF sample, and SF sample had higher comprehensive principal component values. MWF takes less time than IRF, which operated at 2,450 MHz (full power of 700 W) for 2 min. Therefore, MWF was the most suitable fixation method for sea buckthorn leaf tea. Practical Applications. Leaf tea is the main product of sea buckthorn leaf. However, at present, the quality of sea buckthorn leaf tea in the market is uneven, the processing methods are diverse, and there is no certain quality standard. This paper provides some data support and theoretical support for the production, processing, and purchase of sea buckthorn leaf tea.

Effect of fixation methods and various clones of Camellia sinensis var. sinensis (L) properties and antioxidant activity of Indonesian green tea

Fixation is essential in green tea processing to inactivate the polyphenol oxidase enzyme. In Indonesia, green tea is made from the Assam variety and produced using the panning method. Few studies are reported on green tea made from Indonesian clones of the Sinensis variety. This study aims to identify chemical characteristics, antioxidant activity, and sensory evaluation of green tea from local clones of the Sinensis variety (GMBS 2, GMBS 4, and GMBS 5) with different fixation methods (panning and steaming). The results show that the caffeine content of green tea products ranged from 2.51-2.59% and 2.67-2.74% for panning and steaming methods. The panning method produced green tea with higher total polyphenol and flavonoid content than the steaming method. Green tea with the panning method has an IC50 value of 14.45; 14.41; and 17.41 mg/L for GMBS 2, GMBS 4, and GMBS 5, respectively. The panning method resulted in a smaller IC50 value than the steaming method for GMBS 2 and GMBS 4 clones. The steaming method produced green tea with a higher taste, aroma, and total score than those the panning method. However, different fixation methods did not significantly affect the appearance, liquor color, and leaf infusion. In conclusion, different fixation methods on GMBS 2, GMB 4, and GMB 5 produced green tea products that met the Indonesian National Standard 3945:2016. Further research is needed to determine the role of the plucking period/season and the characteristics of volatile compounds of green tea from GMBS clones with different fixation methods.