## 3 Results and Discussion
### Phenolic Compounds, Flavonoids and Antioxidant Activity of the Red Propolis Extracts
It should be noted that the variations in the final concentrations of phenolic compounds may be correlated to differences in the extraction process, as well as the seasonality and geographic origin of the samples [66, 70, 71]. Concerning the differences identified for the flavonoids and antioxidant activity (DPPH), an increase of up to 7% in the flavonoid concentration and a reduction of 23% in the IC\({}_{50}\) were observed in the antioxidant action evaluates, when comparing the samples obtained with the application of ultrasound and the control (Figure 1). Therefore, the  
Figure 1: Analysis of the total content of phenolic compounds, flavonoids and the antioxidant activity (IC\({}_{50}\)) of red propolis extracts obtained in different conditions. Values presenting the same letter in the same analysis do not show significant differences (\(p\) > 0.05) in [PERSON]’s test at 95% confidence. Samples E:UT and E:25\(-\)30 presented values lower than the quantification limit for kaempfer. Average of analyses obtained from triplicates (\(n\) = 3). inclusion of ultrasound pretreatment was effective for finding red propolis extracts with higher antioxidant activities when considering the lower IC\({}_{50}\) values determined here. The extracts obtained under the same temperature conditions, regardless of their duration of ultrasound exposure, did not present significant differences in regard to the flavonoid content, showing that prolonged exposures do not contribute to an increased yield of these compounds. At a temperature of 25 \({}^{\circ}\)C (the same temperature used to obtain the control extract), it was observed that the application of ultrasound did not significantly contribute to an increased total flavonoid content in the extracts. Thus, the increase in the extraction of these compounds may be associated to the application of low temperatures associated with the use of adequate solvents, given the sensitivity of these compounds to high temperatures [72]. The flavonoid content is important information that should be obtained for propolis extracts because it is a quality control parameter within the regulations of countries such as Brazil, Argentina and Switzerland [68]. Flavonoid values lower than the ones in this work were determined by [PERSON] et al. [73] and [PERSON] et al. [38] for red propolis extracts treated with ultrasound that were collected from the same geographic region (0.31 \(\pm\) 0.01 and 31.48 \(\pm\) 0.50 mgQE.g\({}^{-1}\), respectively). Regarding the antioxidant activity, all the extracts obtained at 25 \({}^{\circ}\)C (samples E:25\(-\)10, E:25\(-\)20 and E:25\(-\)30), regardless of the duration of the ultrasound pretreatment, presented the lowest IC\({}_{50}\) values and, consequently, the highest antioxidant activities, given that the lower the effective concentration is, the lower the quantity of extract requisite to oxidize 50% of the DPPH\({}^{\bullet}\) radicals available in the reaction (Figure 1) [74]. These results indicate that the higher the concentration of flavonoid presence in the extracts is, the higher the antioxidant activity of the evaluated sample (as represented by a lower IC\({}_{50}\)), suggesting that these compounds are answerable for the antioxidant activity of propolis [75; 76; 77]. [PERSON] et al. [78] evaluated the red propolis extracts obtained from ethanolic extraction (native to northeastern Brazil) and reported higher IC\({}_{50}\) values (44 to 90 mg\(\cdot\)mL\({}^{-1}\)). Exposure to ultrasound may help to improve the release of intracellular compounds because the cells are easier to rupture, increasing the quantitative availability of these compounds [79]. As mentioned, the variation in the total content of antioxidant compounds obtained when compared with the results from other studies may be related to the geographic origin, seasonality, or extraction method.