## 4 Discussion
As for the stem extracts, this pattern of behavior does not always occur for the hydroalcoholic solvent, but the amount of flavonoids seems to have a greater influence on the antioxidant activity of the Touriga Nacional and Touriga Franca varieties. [PERSON] et al. [40] collected results from several studies on the antioxidant activity of stem extracts from various grape varieties, namely Touriga Nacional, Touriga Franca, Tina Roriz, and Viosinho, among others. Using the FRAP method, Touriga Nacional and Tina Roriz presented values of 257.8 and 235.3 mg TE/g of dry extract, correspondingly, while Viosinho and Touriga Franca exhibited 24 and 30 mM TE/100 g of dry extract, respectively. Since the extraction and quantification conditions are different from those of our study, it is not possible to compare the results. In the case of antioxidant activity, there is no specific analytical method widely used for its evaluation. However, there are several studies determining the antioxidant activity of extracts from stems and seeds of different red grape varieties, such as Pinot Noir, Negro Amaro, Castelao, and Tinto Cao, among others [38; 39; 40; 48]. [PERSON] et al. [39] evaluated the antioxidant activity of extracts from Pinot Noir grape seeds using the DPPH method, using a 70% aqueous ethanol solution as an extracting solvent, and obtained 579.33 \(\pm\) 4.15 \(\upmu\)M TE/g of dry extract. According to [PERSON] et al. [38] the antioxidant activity of extracts from seeds of several varieties was evaluated using a mixture of methanol/water/acetic acid (80:20:5) as an extracting solvent, using the DPPH and FRAP methods. For the DPPH test, for example, the Pinot Noir variety had values of 16,925 \(\pm\) 189 \(\upmu\)mol TE/100 g of dry extract, and Negro Amaro presented values of 7265 \(\pm\) 95 \(\upmu\)mol TE/100 g of dry extract. For the FRAP test, the Pinot Noir variety presents values of 21,492 \(\pm\) 47 \(\upmu\)mol Fe\({}^{2+}\)/100 g of dry extract, and the Negro Amaro of 9447 \(\pm\) 49 \(\upmu\)mol Fe\({}^{2+}\)/100 g of dry extract. The values obtained by the FRAP method are higher than those of the DPPH, which is generally also verified in our study for seeds and stems. This was already expected since DPPH is a colorimetric method subject to various interferences. Fungi and bacteria are responsible for most infections and the mortality associated with them [49; 50], namely because of antimicrobial resistance [49; 51; 52; 53; 54; 55; 56; 57]. The antimicrobial activity of parts of the vine has already been described in several scientific papers [17; 18; 26; 33; 44]. Some parts of the grapevine, such as grape seeds, grapes, and pomace, have been identified as having antifungal activity against yeasts and filamentous fungi, and the mechanisms of action described were diverse, such as altering ergosterol synthesis, interfering with fungal enzyme activity, reducing fungal cell adherence, or inducing fungus apoptosis [17]. For bacteria, the interference of compounds from grapes with Gram-positive and Gram-negative strains was also referred to [18], and one of the mechanisms of action already reported for seeds, pomace, steams, or leaves, among others, was the interference with bacterial biofilms [58]. In our work, and for all the varieties tested, the hydroalcoholic extract of the grains was the only one that showed antimicrobial activity, while the others showed no activity at the maximum concentration of 200 \(\upmu\)g/mL. However, when tested at the same concentration, none of the stalk extracts showed antimicrobial activity. According to our results, ethanol is the solvent that allows the extraction of the greatest content of phenolic compounds and flavonoids. However, the extract that showed the best activity was hydroalcoholic. Furthermore, the phenolic and flavonoid contents were lower in seeds than in stems. It seems, based on our results, that the antimicrobial activity does not seem to depend on the total phenolic or flavonoid content of the extract.