## 3 Results and Discussion
### Quantification of Flavonoids, Total Phenolic Content and Antioxidant Activity  
Notably, our results revealed the dominance of rutin (31.17 ug/mL) compared to the other flavonoids, followed by luteolin (14.46 ug/mL), isorhamentin hexoside-pentoside (2.68 ug/mL), quercetin hexoside (2.33 ug/mL), kaempfer hexoside-pentoside (0.609 ug/mL), catechin (1.73 ug/mL), quercetin (0.082 ug/mL) and naringenin (0.024 ug/mL). The estimated value of the total phenolic content of the extract expressed as mg of GAE per g of dry material was 120.56 \(\pm\) 2.25 GAE/g. The antioxidant activity of the extract was evaluated by DPPH and ABTS assays and the results were expressed as IC\({}_{50}\) values. _S. aspera_ aerial parts exhibited a notable antioxidant activity which corresponds to 13.9 \(\pm\) 1.91 ug/mL for the DPPH method and 6.27 \(\pm\) 1.7 ug/mL for the ABTS method. Various studies dealing with total phenolic content and the antioxidant activity of several _Smilax_ spp. have been published in the last decades. Underground plant organs, i.e., roots and rhizomes, have been intensively studied [16], while the antioxidant activity of leaves and stems of certain species has also been examined [16; 27; 28]. All studied species have shown a notable antioxidant activity which in some cases was comparable to that of strong synthetic scavengers and was strongly correlated to their phenolic content [29; 30]. In our study, _S. aspera_ exhibited a high phenolic content and significant antioxidant activity. By comparing the calculated IC\({}_{50}\) values to known antioxidants [trolox (the IC\({}_{50}\) value corresponds to 4.53 \(\pm\) 1.89 ug/mL for the DPPH assay and to 2.66 \(\pm\) 0.90 ug/mL for the ABTS assay) and caffe acid (the IC\({}_{50}\) value is equal to 2.36 \(\pm\) 0.61 ug/mL and 1.72 \(\pm\) 1.29 ug/mL for DPPH and ABTS assay, respectively)], it is concluded that the plant under study can be classified among those with potent antioxidant capacity. Only a few studies have investigated the antioxidant activity of _S. aspera_. The study of [31], evaluated the non-polarfraction of the leaves, in terms oftocopherol content. Furthermore, [32], examined the antioxidant activity of leaves and fruits from _S. aspera_ from different regions with the FRAP assay. The calculated antioxidant activity regarding leaves ranges from 62.97 to 64.57 mmol Fe\({}^{+2}\)/kg while for the fruits of the plant, this value is from 64.51 to 66.31 mmol Fe\({}^{+2}\)/kg. Both studies concluded that _S. aspera_ is a good source of antioxidants. Our results confirm the previous findings and add novel knowledge to the field of natural antioxidants. Phenolic compounds belong to a class of chemicals consisting of one or more hydroxyl groups (-OH), bonded to an aromatic ring. Therefore, they can donate an electron or a hydrogen atom to a free radical, interrupting in this way the free radical chain reaction. As a result, there is a strong correlation between the total phenolic content of a plant and its antioxidant activity [33]. Indeed, in our study, the estimated values of the total phenolic content and the antioxidant capacity of _S. aspera_ leaves and stems confirmed this statement. Although phenolic compounds are endowed with many pharmacological properties, they are mostly known for their radical scavenging activity. As numerous diseases are strongly correlated with high concentrations of free radicals in cells and tissues, phenolic compounds may play a beneficial key role in the prevention of different pathological conditions. However, there is a strong rationale between flavonoid structure and their antioxidant activity. In the study of [34], it is reported that the antioxidant activity of a flavonoid increases when a hydroxyl group is attached to the position C-3 of the C ring, simultaneously to the presence of a 2,3 double bond conjugated to a 4-keto function at the same ring. In addition, the authors also demonstrated that the ortho 3'-4'-dihydroxy moiety at the B ring is important as it enhances the antioxidant capacity of a flavonoid.