Mechanisms and quality variations of non-volatile and volatile metabolites in black tea from various ages of tea trees: Insights from metabolomics analysis

Abstract

The sensory quality of black tea (BT) influenced by various factors, among which tree age is particularly significant. People prefer BT produced by fresh leaves from old tea trees, yet the correlation between tree age and tea quality has not been thoroughly investigated. In this study, we analyzed the quality of BT from young trees (H-JYH) and old trees (H-OJYH) using e-tongue technology and sensory evaluation. Our findings revealed that H-OJYH had stronger sweetness and sourness, richer flavor, and diminished bitter-astringency compared to H-JYH. 1231 non-volatile metabolites and 504 volatile metabolites were discovered by ultra-performance liquid chromatography (UPLC) and gas chromatography-mass spectrometry (GC-MS). L-tartaric acid and trans-citridic acid were found to contribute to increase acidity, and 7,8-dihydroxy-6-methoxycoumarin and d-fructose 6-phosphate were associated with enhanced sweetness in H-OJYH. Additionally, lower levels of octyl gallate and vanillic acid in H-OJYH contributed to the diminished bitter-astringency. β-ionone, 2-phenylethanol and phenylacetaldehyde merged as characteristic compounds of older tree BT with stronger floral and sweet aroma. Our study serves as a guideline to explore the relationship between tree age and tea quality.

Keywords: Age; Aroma, characteristics; Black tea; Flavor.

Fig. 1

Quality analysis of black teas from old tree and new tree. (A) Traditional sensory evaluation results; (B) Electronic tongue results.

Fig. 2

Overview of all non-volatile metabolites of black teas from old tree and new tree. (A) Principal component analysis (PCA) plot; (B) The plot of variance explained by each principal component; (C) Heatmap for correlation analysis; (D) Clustering heat map; (E) Classification chart for all non-volatile metabolites; (F) Trends of the all non-volatile metabolites change in different tree ages. Note: PC1 denotes the first principal component, PC2 denotes the second principal component, PC3 denotes the third principal component, and the percentage denotes the explanation rate of that principal component for the dataset. Each point in the plot denotes a sample, and samples from the same group are represented using the same color.

Fig. 3

Overview of all volatile metabolites of black teas from old tree and new tree. (A) Principal component analysis (PCA) plot; (B) The plot of variance explained by each principal component; (C) Heatmap for correlation analysis; (D) Clustering heat map; (E) Classification chart for all volatile metabolites; (F) Trends of the all volatile metabolites change in different tree ages. Note: PC1 denotes the first principal component, PC2 denotes the second principal component, PC3 denotes the third principal component, and the percentage denotes the explanation rate of that principal component for the dataset. Each point in the plot denotes a sample, and samples from the same group are represented using the same color.

Fig. 4

Differential analysis of non-volatile metabolites between old tree black tea and new tree black tea, including (A) Volcano maps and (B) K-Means plot.

Fig. 5

Differential analysis of volatile metabolites between old tree black tea and new tree black tea. (A) Pie chart of the categories of volatile different metabolites; (B) Volcano maps; (C) Fold Change of volatile differential metabolites within top 10; (D) VIP value map of volatile differential metabolites within top 10.