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Figure 1. 

Manufacturing processes of Orthodox Keemun black tea (Keemun congou black tea).

Figure 2. 

Sensory evaluation and main taste compounds in the four Keemun black teas.

Figure 3. 

Nonvolatile profiles of the four Keemun black teas detected by LC-MS/MS.

Figure 4. 

Identification of differential nonvolatiles between four Keemun black tea types. (a) Principal component analysis (PCA); (b) hierarchical clustering analysis; (c) and (d) orthogonal partial least squares discriminant analysis (OPLS-DA) and differential metabolites between MF and JZ teas; (e) and (f) OPLS-DA analysis and differential metabolites between MF and CG teas.

Figure 5. 

Thermal treatments of MF black tea samples. (a) PCA; (b) differential nonvolatiles (VIP ≥ 1).

Figure 6. 

Metabolite profiles of bud (BT), leaf (LT), and stem (ST) black tea. (a) Concentration proportion of nonvolatile and volatile compounds in BT, LT and ST; (b) nonvolatiles with a high concentration in BT; (c) nonvolatiles with a high concentration in BT and LT; (d) nonvolatiles with a high concentration in LT an ST.