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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.

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.

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.