*3.4. Principal Component Analysis*

The PCA was carried out to clarify the relationship between the different growth stages of amaranth aerial parts and the evaluated variables. The data set obtained for 16 phenolic compounds, five antioxidant assays, and TPC with respect to seven growth stages was subjected to PCA. The results are presented in Figure 4. The first two principal components (PC1 and PC2) significantly explained most of the variations–87.08% of the total variance. The clustering of growth stages with three separate groups: 1–vegetative stages (early, medium, and late vegetative), 2–shooting and budding stages, and 3–early flowering and grain fill stages was obtained as shown in plot A (Figure 4). The variables that were differentiating distribution of each growth stage were depicted in plot B (Figure 4). The early, medium, and late vegetative stages were associated with the most antioxidant assays: TEAC, FRAP, PCL-ACL, and Fe2<sup>+</sup> chelating ability. The TPC and content of some hydroxycinnamic acid derivatives (compounds **1**–**5**, **7**, **10**–**12**, **14**, and **16**) also affected this group of stages. In turn, the third group of growth stages (early flowering and grain fill) was clearly related to content of flavonols and three remaining hydroxycinnamic acid derivatives (compounds **6**, **8**, and **9**). The DPPH assay was negatively correlated with other antioxidant activity assays because the EC50 values were used in PCA. In the plot, the DPPH assay influenced the distribution of shooting and budding stages due to their low DPPH• scavenging activity with high EC50 values.

**Figure 4.** Principal component analysis (PCA) plots of the data set of variables: Total phenolic content (TPC), individual phenolic compound (**1**–**16**), and antioxidant assays obtained for amaranth in different growth stages. EV, early vegetative; MV, medium vegetative; LV, late vegetative; S, shooting; B, budding; EF, early flowering; GF, grain fill; TEAC, Trolox equivalent antioxidant capacity; FRAP, ferric-reducing antioxidant power; PCL-ACL, antioxidant capacity in photochemiluminescence assay; CHEL, Fe2<sup>+</sup> chelating ability. (**A**): Distribution of growth stages, (**B**): Distribution of variables.
