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Anxi Tieguanyin belongs to the oolong tea category and is one of the top ten most famous teas in China. In this study, hyperspectral imaging (HSI) technology was combined with chemometric methods to achieve the rapid determination of free amino acid and tea polyphenol contents in Tieguanyin tea. Here, the spectral data of Tieguanyin tea samples of four quality grades were obtained via visible near-infrared hyperspectroscopy in the range of 400–1000 nm, and the free amino acid and tea polyphenol contents of the samples were detected. First derivative (1D), normalization (Nor), and Savitzky–Golay (SG) smoothing were utilized to preprocess the original spectrum. The characteristic wavelengths were extracted via principal component analysis (PCA), competitive adaptive reweighted sampling (CARS), and the successive projection algorithm (SPA). The contents of free amino acid and tea polyphenol in Tieguanyin tea were predicted by the back propagation (BP) neural network, partial least squares regression (PLSR), random forest (RF), and support vector machine (SVM). The results revealed that the free amino acid content of the clear-flavoured Tieguanyin was greater than that of the strong-flavoured type, that the tea polyphenol content of the strong-flavoured Tieguanyin was greater than that of the clear-flavoured type, and that the content of the first-grade product was greater than that of the second-grade product. The 1D preprocessing improved the resolution and sensitivity of the spectra. When using CARS, the number of wavelengths for free amino acids and tea polyphenols was reduced to 50 and 70, respectively. The combination of 1D and CARS is conducive to improving the accuracy of late modelling. The 1D-CARS-RF model had the highest accuracy in predicting the free amino acid (RP2 = 0.940, RMSEP = 0.032, and RPD = 4.446) and tea polyphenol contents (RP2 = 0.938, RMSEP = 0.334, and RPD = 4.474). The use of hyperspectral imaging combined with multiple algorithms can be used to achieve the fast and non-destructive prediction of free amino acid and tea polyphenol contents in Tieguanyin tea. [ABSTRACT FROM AUTHOR]

To explore the effects of fresh leaves harvested at different picking periods on aroma quality and chemical characteristics of oolong tea, morning leaves and evening leaves of Tieguanyin were selected as materials and turned into morning tea and evening tea according to the traditional technology. The volatile components of fresh leaves and oolong tea were analyzed by the method of gas chromatography-mass spectrometer (GC-MS), in order to compare their differences between morning oolong tea and evening oolong tea. The results showed that total volatile components of evening tea were 28.3% less than that of morning tea. The content and proportion of alcohol compounds were superior, especially isophytol and trans-nerolidol. The characteristics of volatile components in fresh leaves were different from that in oolong tea. The rate of alcohol compounds was close to that of acid compounds in fresh leaves, while in oolong teas the difference was large. Two kinds of fresh leaves had 56 identical components, that were 4 more than the two kinds of oolong tea. However, among 42 common components of fresh leaves and oolong tea, palmitic acid, dihydroactinidiolide, trans-nerolidol and isophytol were obviously affected by the manufacture technology, and their variation amplitudes were large. It can be seen that the distribution characteristics of volatile compounds of evening leaves and morning ones were different, and the aroma quality of evening tea was better than that of morning tea, especially the refreshing aroma.

Anxi Tieguanyin belongs to the oolong tea category and is one of the top ten most famous teas in China. In this study, hyperspectral imaging (HSI) technology was combined with chemometric methods to achieve the rapid determination of free amino acid and tea polyphenol contents in Tieguanyin tea. Here, the spectral data of Tieguanyin tea samples of four quality grades were obtained via visible near-infrared hyperspectroscopy in the range of 400–1000 nm, and the free amino acid and tea polyphenol contents of the samples were detected. First derivative (1D), normalization (Nor), and Savitzky–Golay (SG) smoothing were utilized to preprocess the original spectrum. The characteristic wavelengths were extracted via principal component analysis (PCA), competitive adaptive reweighted sampling (CARS), and the successive projection algorithm (SPA). The contents of free amino acid and tea polyphenol in Tieguanyin tea were predicted by the back propagation (BP) neural network, partial least squares regression (PLSR), random forest (RF), and support vector machine (SVM). The results revealed that the free amino acid content of the clear-flavoured Tieguanyin was greater than that of the strong-flavoured type, that the tea polyphenol content of the strong-flavoured Tieguanyin was greater than that of the clear-flavoured type, and that the content of the first-grade product was greater than that of the second-grade product. The 1D preprocessing improved the resolution and sensitivity of the spectra. When using CARS, the number of wavelengths for free amino acids and tea polyphenols was reduced to 50 and 70, respectively. The combination of 1D and CARS is conducive to improving the accuracy of late modelling. The 1D-CARS-RF model had the highest accuracy in predicting the free amino acid (RP2 = 0.940, RMSEP = 0.032, and RPD = 4.446) and tea polyphenol contents (RP2 = 0.938, RMSEP = 0.334, and RPD = 4.474). The use of hyperspectral imaging combined with multiple algorithms can be used to achieve the fast and non-destructive prediction of free amino acid and tea polyphenol contents in Tieguanyin tea.

In order to investigate the effect of wrapping-rolling on the quality of Tieguanyin oolong tea, non-volatile and volatile metabolites in rolled tea leaves before and after repeated wrapping-twisting for up to three times were analyzed by widely targeted metabolomics based on headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results showed that a total of 973 non-volatile metabolites belonging to 12 categories were identified, including 468 differential metabolites. The total amount of non-volatile metabolites showed a decreasing trend during the wrapping-twisting process. Particularly, the decrease in the content of differential metabolites such as flavonol glycosides and phenolic acids contributed to the reduction in bitterness and astringency during the wrapping-twisting process. The content of differential lipids increased, which provided favorable conditions for the conversion of volatile fatty acids during the subsequent drying process. A total of 47 volatile components belonging to six categories were identified. During the wrapping-twisting process, the contents of β-red myrcene, heptanal, (E)-2-hexenyl hexanoate and cis-3-hexenyl isobutyrate, responsible for fatty or grassy aroma, decreased, while the contents of methyl jasmonate, benzyl benzoate, geranyl acetone and 3,7-dimethyl-1,5,7-octatrien-3-ol, contributing to floral or fruity aroma, increased. It was noteworthy that the odor activity value (OAV) of the major aroma components in Tieguanyin oolong tea, such as linalool, jasmonolactone, cis-jasmonone, α-farnesene and basilene, were still greater than 1 at the end of the wrapping-twisting process although their contents decreased during this process. It could be seen that the wrapping-twisting process was beneficial to purify the quality of Tieguanyin tea, and provided it with a more mellow taste and more obvious floral and fruit aromas. This study provides new insights into the metabolite changes and the flavor formation of oolong tea during the wrapping-twisting process.

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The effects of different processing procedures on the aroma and quality components of Anxi Tieguanyin were studied, to provide a certain scientific basis for improving further development of Tieguanyin. In this study, Tieguanyin was processed according to the production process of Anxi Tieguanyin. The changes of aroma components, tea polyphenols, caffeine, free amino acids, flavonoids, tea pigments and other important internal components of Tieguanyin were investigated. Significant differences of the component contents were observed in different processing stages. The content of tea polyphenols and caffeine showed an overall downward trend. The content of tea polyphenols and caffeine were decreased by 68.52% and 47.74% during the entire processing process, while the content of amino acids and flavonoids showed an overall upward trend. The amino acids content during the entire processing process was increased by 59.67% and the flavonoids content was increased by 1.62 times. The content of tea pigments showed no obvious changes. Among them, the Shaqing process had the greatest impact on the color and fragrance components of Tieguanyin during the processing. After the Shaqing process, the content of tea polyphenols was decreased by 40.66%, and the content of flavonoids significantly was increased to 6.93 mg/g, which was the key processing node. In addition, Shaiqing, Yaoqing and Liangqing were also important processes that affected the aroma and quality of Tieguanyin. This article provided scientific basis for the quality improvement and process optimization of Anxi Tieguanyin.

Lanthanum can affect the growth and development of the tea plant. Tieguanyin (TGY) and Shuixian (SX) cultivars of Camellia sinensis were selected to explore the mechanism underlying the accumulation of lanthanum (tea plants' most accumulated rare earth element) through proteomics. Roots and fresh leaves of TGY and SX with low- and high-accumulation potential for lanthanum, respectively, were studied; 845 differentially expressed proteins (DEPs) were identified. Gene ontology analysis showed that DEPs were involved in redox processes and related to molecular functions. Kyoto Encyclopedia of Genes and Genomes metabolic pathway analysis showed that DEPs were associated with glutathione (GSH) and α-linolenic acid metabolism, plant pathogen interaction, and oxidative phosphorylation. Thirty-seven proteins in the GSH metabolism pathway showed significant differences, wherein 18 GSH S-transferases showed differential expression patterns in the root system. Compared with the control, expression ratios of GST (TEA004130.1) and GST (TEA032216.1) in TGY leaves were 6.84 and 4.06, respectively, after lanthanum treatment; these were significantly higher than those in SX leaves. The LOX2.1 (TEA011765.1) and LOX2.1 (TEA011776.1) expression ratios in the α-linolenic acid metabolic pathway were 2.44 and 6.43, respectively, in TGY roots, which were significantly higher than those in SX roots. The synthesis of specific substances induces lanthanum-associated defense responses in TGY, which is of great significance for plant yield stability. [ABSTRACT FROM AUTHOR]

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

Previously, we found that three types of Tieguanyin tea (Tgy-Q, Tgy-N and Tgy-C) extracts could alleviate Alzheimer's disease (AD) in a mouse model among which Tgy-C was more effective. In this study, APP/PS1 transgenic mice were used to investigate the metabolomic changes in the feces of mice treated with Tieguanyin tea extracts. Results showed that the profile of fecal metabolites was obviously changed in AD mice. Metabolomics analysis found the effects of Tgy-C, especially its decreasing effect on the fecal metabolites in AD mice—132 of the 155 differential metabolites were decreased. KEGG enrichment revealed that differential metabolites could participate in functional pathways including protein digestion and absorption, biosynthesis of amino acids and ABC transporters. Further comparisons of the metabolites between groups showed that although Tgy-N and Tgy-Q exerted a decreasing effect on the fecal metabolites, Tgy-C was more effective. Moreover, correlation analysis found that the levels of the fecal metabolites were highly correlated with the contents of functional components in tea extracts. Finally, 16S rDNA sequencing presented that Tieguanyin extracts modified the gut microbiota by targeting diverse bacteria. In this study, we investigated the differences of three types of Tieguanyin tea extracts on the fecal metabolites as well as the bacterial community of the gut microbiota in AD mice. The identified differential metabolites and the changed intestinal bacteria might provide potential diagnostic biomarkers for the occurrence and progression of AD. [ABSTRACT FROM AUTHOR]

The color and taste of tea infusion play crucial roles in assessing tea quality. While color can be easily quantified, taste perception is subjective in nature. Can the color of tea infusion directly reflect its taste? In this study, spectroscopy and metabolomics techniques combined with machine learning algorithms, were used to identify the key compounds that responsible for both color and taste in Qingxiang Tieguanyin (QXTGY) tea infusion. The results showed strong correlations between almost all of 46 differential compounds and the taste profile of the tea infusion. Notably, quercetin 3- O -glucosyl rutinoside, rutin, and quercetin 3- O -glucoside were found to establish a connection between the color and taste of QXTGY tea infusion. Specifically, within a certain range, these compounds promoted a darker color (deepening the yellowness) in the tea infusion while simultaneously reducing its umami and brisk taste. This indicates that the color of tea infusion can reflect its taste to some extent. Furthermore, quercetin 3- O -glucosyl rutinoside had the most significant impact on the color of the tea infusion. The findings of this study offer an alternative objective approach to evaluate the taste of tea infusion by objectively determining its color. • Machine learning algorithm was applied in this study. • Three compounds established a connection between the color and taste of tea infusion. • Quercetin 3- O -glucosyl rutinoside had the most significant impact on the color of tea infusion. [ABSTRACT FROM AUTHOR]

Previously, we found that three types of Tieguanyin tea (Tgy-Q, Tgy-N and Tgy-C) extracts could alleviate Alzheimer’s disease (AD) in a mouse model among which Tgy-C was more effective. In this study, APP/PS1 transgenic mice were used to investigate the metabolomic changes in the feces of mice treated with Tieguanyin tea extracts. Results showed that the profile of fecal metabolites was obviously changed in AD mice. Metabolomics analysis found the effects of Tgy-C, especially its decreasing effect on the fecal metabolites in AD mice—132 of the 155 differential metabolites were decreased. KEGG enrichment revealed that differential metabolites could participate in functional pathways including protein digestion and absorption, biosynthesis of amino acids and ABC transporters. Further comparisons of the metabolites between groups showed that although Tgy-N and Tgy-Q exerted a decreasing effect on the fecal metabolites, Tgy-C was more effective. Moreover, correlation analysis found that the levels of the fecal metabolites were highly correlated with the contents of functional components in tea extracts. Finally, 16S rDNA sequencing presented that Tieguanyin extracts modified the gut microbiota by targeting diverse bacteria. In this study, we investigated the differences of three types of Tieguanyin tea extracts on the fecal metabolites as well as the bacterial community of the gut microbiota in AD mice. The identified differential metabolites and the changed intestinal bacteria might provide potential diagnostic biomarkers for the occurrence and progression of AD.

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

Tieguanyin tea is a typical representative of oolong tea in China, and is famous for its orchid-like aroma. Fatty acids are one of the important precursors for aroma production. However, fatty acid contents and compositions in Tieguanyin largely remain undefined. In this study, we quantified the fatty acid composition in Tieguanyin and its offspring by gas chromatography–flame ionization detector, and compared the effects of growth sites and harvest time on the leaf fatty acid composition. The results showed that total fatty acid contents in Tieguanyin fresh leaves were higher than its offspring. Growth sites had significant impacts on fatty acid contents. Tieguanyin grown in Anxi County showed higher total fatty acid contents, and higher ratio of total unsaturated fatty acids to total saturated fatty acids. The fresh leaves in the morning showed higher total fatty acid contents compared to samples harvested in the afternoon or evening, suggesting a dynamic fatty acid degradation during day period. During tea processing, unsaturated fatty acids including linolenic acid, linoleic acid and oleic acid (18:1Δ9c) decreased 13.1%, 13.2% and 84.2%, respectively. The ratio of unsaturated fatty acids to saturated fatty acids still was above 300%. We found that Tieguanyin was a typical 18:3 plant, and the higher ratio of unsaturated fatty acids to saturated fatty acids of Tieguanyin grown in Anxi County may contribute to its characteristics aroma. [ABSTRACT FROM AUTHOR]

Aged Tieguanyin has a unique, long-lasting aged aroma. However, a lack of research has hindered further improvements in its quality. This study analyzed the compounds contributing to the aroma of Tieguanyin at different aging times and correlated the results with microorganisms to explore the underlying aging mechanism, using headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME/GC-MS) and MiSeq methods. A total of 85 volatile compounds were identified. The volatiles in tea aged for over 11 years were stable, similar, and significantly different from those of unaged tea. The 13 upregulated discriminatory volatiles in the late aging period were speculated to be the characteristic compounds constituting the aged aroma: 2-heptanone, 2-nonanone, 6,10-Dimethylundecan-2-one, dehydro-β-ionone, β-ionone epoxide, (−)-α-terpineol, 1-octen-3-ol, linalool oxide (II), propanoic acid, butanoic acid, 5-hydroxymethylfurfural, safranal, and caffeine. These compounds are mainly produced through the enzymatic degradation pathway of carotenoids, glycosides hydrolysis, and lipids oxidation. Based on Spearman's correlation analysis, bacteria and fungi had strong interactions with aged aroma compounds. Specifically, Sphingomonas , Acinetobacter , Halomonas , Trichosporon , Aspergillus , and Cyberlindnera were the core functional microorganisms of aged Tieguanyin. These genera had the potential to promote the formation of aged aroma through the accumulation of metabolic precursors. • The volatile components of aged Tieguanyin were determined. • The aged aroma compounds are mainly produced by carotenoids, glycosides, and lipids degradation. • Seven years is a special stage in the aging process of Tieguanyin. • Six core functional microorganisms have strong positive correlations with the aged aroma compounds. [ABSTRACT FROM AUTHOR]