## 2 Results and Discussion
### Biological Activity  
#### 2.5.1 Antioxidant Activity  
Plants produce a broad spectrum of bioactive compounds, like phenolic acids, flavonoids, and anthocyanins; they contain one or more hydroxyl groups that are attached to either a phenyl ring or classes such as carotenoids. These compounds are important because they may impact several functions in humans, given that they act as antioxidants [41]. Phenolic compounds are unique oxygen radical scavengers because the electron reduction potential of phenolic radicals is lower than that of oxygen radicals, and they are usually less reactive than oxygen radicals [8; 41].  
Table 2 shows the results from the antioxidant assays of bee pollen samples. Accordingly, the highest DPPH\({}^{\bullet}\) radical scavenging activity was reached in the BP7 sample, with EC\({}_{50}\): 0.07 \(\pm\) 0.00 mg/mL, followed by BP2 (0.15 \(\pm\) 0.00 mg/mL) and BP6 (0.20 \(\pm\) 0.02 mg/mL). In the ABTS\({}^{\bullet+}\) test, the highest value was recorded in BP4, at 1.59 \(\pm\) 0.15 mM Trolox/mg, followed by BP6, BP7, and BP2, at similar values. BP1 and BP5 samples were the lowest performers in both DPPH\({}^{\bullet}\) and ABTS\({}^{\bullet+}\) tests. It seems that samples with higher values for total phenolic and flavonoid compounds tend to show higher DPPH\({}^{\bullet}\) and ABTS\({}^{\bullet+}\) radical scavenging activity. This trend was evaluated via correlation analysis, and as is evident in Table 5, the total phenolic compounds were moderately correlated with DPPH\({}^{\bullet}\)/ABTS\({}^{\bullet+}\) (r = 0.589/0.543), confirming the observation made in numerous other studies concerning bee pollen samples of various plant origins [10; 16; 25]. The moderate correlation with the antiradical assays can be related to other compounds present in bee pollen composition, as well as antioxidant activity, such as carotenoids [42].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Assay** & **r** & **Significance Level (_p_ Value)** \\ \hline TPC–DPPH\({}^{\bullet}\) & 0.589 & 0.164 \\ TPC–ABTS\({}^{\bullet+}\) & 0.543 & 0.208 \\ TPC–Reducing power & 0.071 & 0.879 \\ TPC–DPPH\({}^{\bullet}\) & 0.247 & 0.593 \\ TPC–ABTS\({}^{\bullet+}\) & 0.106 & 0.822 \\ TPC–Reducing power & 0.216 & 0.642 \\ \hline \hline \end{tabular} Twenty–one paired average samples from each test were used in the comparison. r value represents Pearson’s linear correlation value. The level of significance was expressed as \(p\) \(<\) 0.05.  
\end{table}
Table 5: Correlation analysis between total phenolic compounds and antioxidant capacity.  
The reducing power test was recorded in a range varying between a minimum of 0.02 \(\pm\) 0.01 mg GAE/g (BP1 and BP4) and maximum of 0.09 \(\pm\) 0.0 mg GAE/g (BP3) (Table 2). Surprisingly, the BP3 sample exhibited the highest reducing power activity, even though both the total phenolic/flavonoid and LC-MS results revealed that it exhibited a moderate total bioactive compound, as compared with the other samples. This was likely because of the diversity of the compounds in BP3's composition, rather than its total bioactive compounds. As previously shown by [PERSON] et al. [43], higher antioxidant activity may depend on the position of the functional group in the phenolic structure; the authors demonstrated that the H atoms of the attached hydroxyl groups (\(o\)-diphenyl), at different locations of the rings (A, B, and C), as well as the double bonds of the benzene ring, and the double bond of the oxo functional group (\(\sim\)C=O), of some flavonoids provide compounds with a higher antioxidant capacity. Overall, considering the results of the different assays which predict antioxidant activity, the monofloral bee pollen samples from _Ligustrum/Olea_ sp., _Rubus_ sp., and _Castanaea_ sp. exhibited better results.