## 3 Results and Discussions  
### Total Phenolic Content (TPC)  
Polyphenols are among the major secondary metabolites in medicinal and dietary plants known to possess important biological activities particularly antioxidant abilities [12]. Therefore, the assessment of TPC in the studied extracts is very important. Table 1 summarizes the TPC in the _Centaurea_ extracts. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Plants**} & \multirow{2}{*}{**Extracts**} & **TPC** & **DPPH** & **RP EC50** \\  & & **(mg GAE/g)** & **IC50 (mg/mL)** & **(mg/mL)** \\ \hline \multirow{8}{*}{**Centaurea**} & Hexane (H) & 18.34a \(\pm\) 0.31 & 0.49a \(\pm\) 0.01 & 6.28a \(\pm\) 0.77 \\  & Chloroform (C) & 43.06b \(\pm\) 0.16 & 0.58a \(\pm\) 0.02 & 12.36b \(\pm\) 0.41 \\  & Methanol (M) & 61.12c \(\pm\) 0.60 & 0.59a \(\pm\) 0.01 & 8.77c \(\pm\) 0.16 \\  & Ethanol (ultrasonic) (UE) & 42.73b \(\pm\) 0.36 & 0.94a \(\pm\) 0.01 & 5.15a \(\pm\) 0.09 \\  & supercritical (I) (SFE(I)) & 4.79d \(\pm\) 0.15 & 30.93b \(\pm\) 1.24 & 65.17d \(\pm\) 2.93 \\  & supercritical (II) (SFE(II)) & 13.17e \(\pm\) 0.05 & 21.22c \(\pm\) 0.50 & 22.44e \(\pm\) 1.12 \\  & essential oil (EO) & 12.64e \(\pm\) 0.20 & 45.10c \(\pm\) 0.27 & 24.32e \(\pm\) 0.46 \\ \hline \multirow{8}{*}{**Centaurea sicula L.**} & Hexane (H) & 8.32a \(\pm\) 0.50 & 25.20a \(\pm\) 1.55 & 21.50a \(\pm\) 0.33 \\  & Chloroform (C) & 28.25b \(\pm\) 0.72 & 1.96b \(\pm\) 0.05 & 7.62b \(\pm\) 0.15 \\  & Methanol (M) & 23.27c \(\pm\) 0.077 & 2.94b \(\pm\) 0.02 & 20.55a \(\pm\) 0.76 \\  & Ethanol (ultrasonic) (UE) & 24.56d \(\pm\) 0.05 & 2.00b \(\pm\) 0.10 & 11.75c \(\pm\) 0.58 \\  & supercritical (I) (SFE(I)) & 8.75a \(\pm\) 0.87 & 28.01c \(\pm\) 1.08 & 22.98d \(\pm\) 0.59 \\  & supercritical (II) (SFE(II)) & 12.29e \(\pm\) 0.21 & 22.25d \(\pm\) 0.62 & 24.30e \(\pm\) 0.90 \\  & essential oil (EO) & 9.28f \(\pm\) 0.27 & 28.36d \(\pm\) 2.01 & 25.05f \(\pm\) 0.68 \\ \hline \hline \end{tabular}  
* Means in the same column followed by different letters at superscript are significantly different (\(p<0.05\)).  
\end{table} 
Table 1: Total phenolic, 2,2-Diphenyl-1-picrylhydrazyl hydrate (DPPH) radical scavenging activities and ferric reducing power of _Centaurea kroumirensis_ (Coss.) and _Centaurea sicula_ L. subsp _sicula_ extracts. Values are expressed as means \(\pm\) SD (\(n=3\)). Analysis of variance (ONE-way ANOVA) was used for comparisons. The values ranged from 61.11 to 4.79 mg GAE/g and from 28.25 to 8.32 mg GAE/g for _C. kroumiensis_ and _C. sicula_, respectively. Polar methanol (M), ethanol (ultrasonic) (UE), and moderately polar chloroform (C) extracts presented the highest concentration of polyphenols for both studied plants, as shown in Figure 1.  
According to the species (Figure 1), the highest polyphenol contents was recorded in _C. kroumiensis_. This plant exhibited 61.117 \(\pm\) 0.599 mg GAE/g in M extract. The C and UE extracts contained similar levels of polyphenolic contents (43.06 \(\pm\) 0.158 and 42.729 \(\pm\) 0.357 mg GAE/g, respectively), which point out that solvent and extraction techniques greatly influence the polyphenolic content of the plant extracts. These findings are in agreement with the previous studies, which reported higher concentrations in polyphenics in the extract that was obtained with methanol and ethanol [21; 31; 32]. However, the essential oil (EO) and supercritical SFE(I-II) extracts that were obtained without co-solvent had the lowest TPC for both _Centaurea_ species. The obtained results are predictable, since there is a positive correlation between the polarity of extraction solvents and TPC [25; 29]. As far as our literature review could ascertain, the _C. kroumiensis_ methanolic extract showed a TPC higher than the one of some other studied _Centaurea_ species. The methanolic extract of _C. drabifolia_ subsp. _detonsa_ exhibited TPC = 40.454 mg GAE/g [33]. [PERSON] et al. [11] reported that the methanolic extract of _C. pulchella_, _C. drabifolia_ subsp. _drabifolia_ and _C.