## 2 Results and Discussion
### Antioxidant Activity  
In recent years, the interest from food industries in natural antioxidants has increased, due to several studies have shown possible adverse effects that may be related to the consumption of synthetic antioxidants [43; 44]. On the other hand, regular consumption of antioxidants is associated with a reduced risk of chronic diseases and the natural ones could replace synthetic antioxidants in foodstuffs [45]. Different plant materials are known to be a natural source of antioxidants, such as herbs, seeds, fruits, vegetables and also their by-products. The interest in these natural antioxidants is not only due to their biological value but also to their economic impact, as most of them may be extracted from food by-products and under-exploited plant parts or species. In order to evaluate the total antioxidant activity of the extracts, three different methods were used, due to the absence of a unique methodology able to reflect the total antioxidant activity of a complex matrix, since the antioxidant activity of food and ingredients is determined by a mixture of different phenolic compounds with different action mechanisms [46]. ABTS and/or DPPH are among the most popular colourimetric methods to evaluate foods' total antioxidant activity. However, ABTS applies to both hydrophilic and lipophilic antioxidants, whereas DPPH applies to hydrophobic [47]. ORAC method has been reported by different authors as a more relevant antioxidant method because it engages a biological radical (peroxyl) source and is a very high sensitivity, mainly used to measure the activity of hydrophilic antioxidants compounds [48]. The antioxidant activity values of BE apple extracts, measured by the three different methods (ORAC, ABTS, DPPH) are shown in Figure 1. The values ranged from 6.74 \(\pm\) 0.42 to 17.26 \(\pm\) 0.50 TE/g DE, from 1.73 \(\pm\) 0.07 to 4.42 \(\pm\) 0.11 AAE/g DE, and from 2.69 \(\pm\) 0.26 to 5.11 \(\pm\) 0.13 mg TE/g DE, respectively for ORAC, ABTS and DPPH. On the ORAC assay, the BE apple extracts obtained by CET showed the highest antioxidant activity (17.26 \(\pm\) 0.50 mg TE/g DE) (\(p\) < 0.05), followed by MAE (14.80 \(\pm\) 0.70 mg TE/g DE) (\(p\) < 0.05). The BE apple extracts obtained by CE (7.44 \(\pm\) 0.41 mg TE/g DM) and UAE (6.74 \(\pm\) 0.42 mg TE/g DE) showed the lower values, without significant differences (\(p\) > 0.05). The ORAC values showed a high positive correlation with the previous values of TPC (R\({}^{2}\) = 0.9886), and the ORAC values were much higher than the values of DPPH and ABTS. This kind of differences in values determined by the different methods was previously reported in our work that aims to develop natural antioxidant extracts from cherries [15] and probably arise from the different chemical structures of used radicals and the distinct mechanisms involved during each methodology. In ABTS and DPPH method, it was evaluated the Single-electron transfer (SET) capacity, and in the ORAC assay the hydrogen atom transfer (HAT) capacity [49]. Moreover, [PERSON] et al. [2] also reported high positive correlation between ORAC and TPC values (R\({}^{2}\) = 0.834) in BE apple extract obtained with 80% acetone/water. Concerning the ABTS results, the BE apple extracts obtained by CET presented higher antioxidant activity (4.42 \(\pm\) 0.11 mg AAE/g DE) (\(p\) < 0.05), followed by MAE (3.92 \(\pm\) 0.25 mg AAE/g DE) (\(p\) < 0.05), and the lowest values were attributed to UAE (2.12 \(\pm\) 0.21 mg AAE/g DE) and CE (1.73 \(\pm\) 0.07 mg AAE/g DE) (\(p\) > 0.05). Likewise,  
Figure 1: Antioxidant activity of different Bravo de Esmolfe apple extracts by ORAC method (expressed as mg TE/g DE), ABTS method (expressed as mg AAE/g DE) and DPPH method (expressed as mg TE/g DE). Different letters (a, b, c, d) mean significant differences between extraction techniques in each antioxidant assay (same color in the graph), determined by [PERSON]’s post-hoc test (\(p\) < 0.05).