## 3 Results and Discussion
### Antioxidants and antioxidant activity
#### 3.3.3 Antioxidant Activity  
In this study, the ABTS\({}^{\bullet+}\) free radical scavenging activity was applied to measure antioxidant activity of methanolic extracts obtained from the dried _Stevia_ leaves. The antioxidant activity determined was 152.4, 163.7, 160.3 \(\upmu\)mol Trolox/g for plants from Polish, Paraguayan and Brazilian plantations, respectively. The dried leaves originated from Polish crops differed significantly from those derived from two other plantations (\(p\leq 0.05\)) (Table 3).  
Differences between high antioxidant activity in Paraguayan and Brazilian _Stevia_ and, at the same time, lower content of polyphenic compounds and vitamin C, compared to Polish _Stevia_, can be explain by higher content of other antioxidants that were not measured, for example, essential oils (sesquiterpen-\(\delta\)-caryophyllene, \(\delta\)-farnesene, humulene, candiene, meridolol and monoterpenes--linalool, terpinen-4-ol, terpineol), chlorofil, xanfofils and others [9; 10; 11; 12; 13; 14].  
According to the literature, the antioxidant activity of the aqueous, methanolic and ethanolic extracts of _S. rebaudiana_ leaves is examined by means of the FRAP (ferrum reducing antioxidant power) and the DPPH\({}^{\bullet}\) (1,1-diphenyl-2-picrylhydrazyl) radical scavenging assays. The scavenging of the DPPH\({}^{\bullet}\) free radical, reported in the _Stevia_ leaf extracts are 68.7, 56.8 and 39.8% for water, methanol and ethanol solvents, respectively, at a 600 \(\upmu\)g/mL sample dilution [59; 60]. In turn, the degree of DDPH\({}^{\bullet}\) free radical scavenging measured by [PERSON] at al. [61] and [PERSON] [62] in water, methanol and ethanol extracts from _S. rebaudiana_ leaves were 64.3, 52.5, and 62.8%, respectively, at a sample dilution of 100 \(\upmu\)g/mL. When analyzed by the FRAP method, the extracts showed similar antioxidant activity [14; 59]. On the other hand, [PERSON] et al. [58], who used water-methanol extract, noted the highest degree (96.9%) of free radical scavenging.  
The values of the antioxidant activity of _S. rebaudiana_, which the aforementioned authors determined by other methods, differ from those obtained in this study. This may result from both the advantages of the method used and its disadvantages. For example, the method with the ABTS\({}^{\bullet+}\) reagent is one of the most precise, because it allows for the measurement of the total antioxidant activity of all antioxidants, both lipophilic and hydrophilic. The value obtained, expressed by the rate of radical reduction (change in color), depends both on the antioxidant concentration in the sample and its power. On the other hand, the DPPH method allows for only the determination of hydrophilic antioxidants [63].  
As shown in this study and in the publications cited, the composition of _S. rebaudiana_ ranges widely. Cultivation environmental factors such as temperature, sunlight exposure, soil composition and pH, fertilization, planting density, growth phase and plant physiology strongly affect chemical composition. Additionally, drying method and storage conditions can modify bioactive compounds content [5; 64].