## 2 Results and Discussion
### Taste-Active Compounds' and Quality Markers' Accurate Quantitative Profiling by LC-UV/DAD  
Tea infusions were then profiled by LC-UV/DAD to quantitatively map non-volatiles responsible for taste and trigeminal perception and for quality features [8; 29]. The analytical method was optimized and verified for the accurate quantification of 19 informative chemicals in a single analytical run. Analytics are listed in Table 3, together with the taste threshold (TT) and average amounts (mg/L) from three replicate infusions for each sample. The analytical method's figures of merit, including precision and accuracy, are discussed in the Experimental section and detailed in Supplementary Table S1 (ST1). Principal Component Analysis was applied to the data matrix (quantitative results) of non-volatiles to evaluate the presence of natural clusters within selected samples. Figure 3a shows the score plot of the first and the second principal components (F1-F2 plane); of note, the variance explained by the first two components is quite high and similar to that resulting from key aroma patterns shown in Figure 1a (58.55% F1, 20.10% F2, for a total variance of 78.65%). Moreover, sample clusters based on taste and quality marker distribution are similar to those shown in Figure 1a generated by volatile patterns. Darjeeling Testa \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Compound Name** & **TT (\(\mu\)g/L)** & **Ceylon** & **Assam** & **Azores** & **Darjeeling** & **Darjeeling** & **Kenya** & **Yunnan** \\ \hline Epigallocatechin \({}^{\text{Q}}\) (EGC) & 159 & 72.38 & 29.24 & 16.09 & 25.27 & 71.08 & 38.62 & 16.61 \\ Catechin \({}^{\text{Q}}\) (C) & 119 & 10.87 & 8.05 & 4.42 & 7.22 & 13.03 & 11.54 & 9.76 \\ Epicatechin \({}^{\text{Q}}\) (EC) & 270 & 41.97 & 19.07 & 12.99 & 14.16 & 25.80 & 24.90 & 19.84 \\ Epigallocatechingallate \({}^{\text{T}\text{Q}}\) (EGCG) & 87.0 & 85.35 & 24.09 & 11.88 & 63.52 & 177.23 & 27.18 & 11.23 \\ Galluccheningallate \({}^{\text{Q}}\) (GCG) & 179 & 8.64 & 5.49 & 2.84 & 3.16 & 4.73 & 3.54 & 5.44 \\ Epicatechingallate \({}^{\text{Q}}\) (ECG) & 115 & 41.40 & 21.90 & 7.92 & 29.68 & 39.79 & 20.31 & 18.80 \\ Catechingallate \({}^{\text{Q}}\) (CG) & 239 & 5.37 & 5.18 & 3.07 & 5.03 & 3.93 & 3.59 & 2.76 \\ Theaflavin \({}^{\text{Q}}\) (TF) & 9.00 & 7.55 & 4.39 & 2.92 & 2.25 & 2.16 & 4.50 & 2.33 \\ Theaflavin-3-gallate \({}^{\text{Q}}\) (TF3) & 10.7 & 8.81 & 7.77 & 3.70 & 3.17 & 2.89 & 5.90 & 3.65 \\ Theaflavin-3-’gallate \({}^{\text{Q}}\) (TF3) & 10.7 & 5.28 & 6.64 & 3.76 & 3.47 & \textgreater{}LOQ & 4.92 & 3.67 \\ Theaflavin-3,3’-gallate \({}^{\text{Q}}\) (TF3-3) & 11.3 & 6.38 & 7.96 & \textgreater{}LOQ & 3.40 & \textgreater{}LOQ & 4.77 & 3.59 \\ Myricetin-3-o-galactoside \({}^{\text{T}}\) (M-3-o-gal) & 1.3 & 2.39 & \textgreater{}LOQ & 0.28 & 0.42 & 0.32 & 1.51 & \textgreater{}LOQ \\ Myricetin-3-o-glucoside \({}^{\text{T}}\) (M-3-o-glucose) & 1.0 & 4.10 & 0.24 & 0.37 & 0.85 & 1.02 & 1.33 & \textgreater{}LOQ \\ Quercetin-3-o-rutinoside \({}^{\text{T}}\) (Rutin) & 0.0009 & 19.58 & 6.68 & 6.39 & 5.16 & 6.34 & 9.55 & 7.63 \\ Quercetin-3-o-galactoside \({}^{\text{T}}\) (Q-3-o-gal) & 0.20 & 4.31 & 2.62 & 1.60 & 1.90 & 2.39 & 4.01 & 1.82 \\ Quercetin-3-o-glucose \({}^{\text{T}}\) (Q-3-o-glucose) & 0.30 & 9.42 & 3.93 & 1.01 & 0.77 & 1.12 & 5.53 & 2.68 \\ Kaempfer-3-o-rutinoside \({}^{\text{T}}\) (K-3-o-rut) & 0.15 & 8.31 & 3.11 & 4.56 & 1.98 & 3.83 & 6.89 & 3.91 \\ Kaempfer-3-o-glucose \({}^{\text{T}}\) (K-3-o-glucose) & 0.30 & 4.19 & 1.32 & 1.07 & 0.62 & 1.24 & 3.50 & 1.43 \\ Caffe \({}^{\text{T}}\) & 97.1 & 250.50 & 290.30 & 143.70 & 241.52 & 265.88 & 263.36 & 228.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Quantitative results on key taste compounds (\({}^{\text{T}}\)) and quality markers (\({}^{\text{Q}}\)) of selected infusions. Amounts are expressed in mg/L and obtained by external calibration technique with LC-UV/DAD analysis. Results are provided as mean of three infusions and two analytical replicates. Taste threshold (TT) is expressed in \(\mu\)g/L [23; 38].