Distinct Changes in Metabolic Profile and Sensory Quality with Different Varieties of Chrysanthemum (Juhua) Tea Measured by LC-MS-Based Untargeted Metabolomics and Electronic Tongue

Abstract

Chrysanthemum tea, a typical health tea with the same origin as medicine and food, is famous for its unique health benefits and flavor. The taste and sensory quality of chrysanthemum (Juhua) tea are mainly determined by secondary metabolites. Therefore, the present research adopted untargeted metabolomics combined with an electronic tongue system to analyze the correlation between the metabolite profiles and taste characteristics of different varieties of chrysanthemum tea. The results of sensory evaluation showed that there were significant differences in the sensory qualities of five different varieties of chrysanthemum tea, especially bitterness and astringency. The results of principal component analysis (PCA) indicated that there were significant metabolic differences among the five chrysanthemum teas. A total of 1775 metabolites were identified by using untargeted metabolomics based on UPLC-Q-TOF/MS analysis. According to the variable importance in projection (VIP) values of the orthogonal projections to latent structures discriminant analysis (OPLS-DA), 143 VIP metabolites were found to be responsible for metabolic changes between Huangju and Jinsi Huangju tea; among them, 13 metabolites were identified as the key metabolites of the differences in sensory quality between them. Kaempferol, luteolin, genistein, and some quinic acid derivatives were correlated with the "astringency" attributes. In contrast, l-(-)-3 phenyllactic acid and L-malic acid were found to be responsible for the "bitterness" and "umami" attributes in chrysanthemum tea. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed that the flavonoid and flavonol biosynthesis pathways had important effects on the sensory quality of chrysanthemum tea. These findings provide the theoretical basis for understanding the characteristic metabolites that contribute to the distinctive sensory qualities of chrysanthemum tea.

Keywords: LC-MS; chrysanthemum (Juhua); electronic tongue; metabolomics; sensory quality; tea.

Figure 1

Appearance and origin of five different species of chrysanthemum. Notes: (J) JinshihuangJu; (X) HuangJu; (H) HanbaiJu; (B) BaoJu; (G) GongJu; (F) diagram of the source of five different varieties of chrysanthemum tea.

Figure 2

The proportions of the various metabolites in chrysanthemum tea samples. Notes: Different color blocks represent items belonging to different chemical classifications, and the percentage represents the items belonging to each chemical classification. The number of metabolites is given as a percentage of all identified metabolites. Metabolites that have no chemical classification are defined as undefined.

Figure 3

Multivariate analysis of chrysanthemum tea samples: (A) The 3D PCA of five different species of chrysanthemum. (B) The PLS-DA plot (X vs. J), R2X = 0.751, R2Y = 0.994, Q2 = 0.979. (C) The OPLS-DA score plot (X vs. J), R2X = 0.753, R2Y = 0.994, Q2 = 0.987. (D) Permutation plot of OPLS-DA, R2 = (0.0, 0.5555), Q2 = (0.0, − 0.6665). Notes: (J) JinshihuangJu; (X) HuangJu; (H) HanbaiJu; (B) BaoJu; (G) GongJu.

Figure 4

Multiple analysis of significant differences in metabolite expression between X and J samples (VIP > 1, p < 0.01): (A) In positive ion mode. (B) In negative ion mode. Notes: the x-coordinate represents the log2 FC value of the differential metabolite, that is, the logarithmic value of the differential multiple of the differential metabolite is taken as the base 2, and the ordinate axis represents significant differential metabolites. The red indicates upregulated differential metabolites, while green indicates downregulated differential metabolites.

Figure 5

Identifying the core metabolites: (A) The KEGG enrichment pathway bubble map between X and J samples. (B) The flavone and flavonol biosynthesis pathways. (C) Heatmap analysis of critical metabolites in the flavone and flavonol biosynthesis pathways. (D) Associations between taste characteristics and metabolite data. Note: (A) Each bubble in the figure represents a metabolic pathway (the top 20 with the highest significance were selected according to p-value). The horizontal coordinate where the bubble is located and the bubble size represent the influence factor size of the path in the topology analysis, and the larger the size, the larger the influence factor. The vertical coordinate where the bubble is located and the bubble color represent the p-value of enrichment analysis (take the negative common logarithm, i.e., −log10 p-value); the darker the color, the smaller the p-value, and the more significant the enrichment degree; the enrichment factor represents the proportion of the number of differential metabolites in this pathway in the total number of annotated metabolites in this pathway. (B) The small circular nodes in the metabolic pathway diagram represent metabolites; the metabolites labeled in red are the significantly upregulated differential metabolites detected in the experiment (VIP > 1, p < 0.05, fold change > 1), while the metabolites labeled in blue are the significantly downregulated differential metabolites detected experimentally (VIP > 1, p < 0.05, fold change > 1). The depth of the color indicates the degree of downward adjustment.