## 2 Results and Discussion
### Antioxidant Components and Antioxidant Activity Assays
#### 2.2.2 Antioxidant Activity Assays  
Total polyphenol contents in UJ and PEFJ samples were determined by the Folin-Ciocalteu reagent (FCR) colorimetric assay, which is based on an electron-transfer (ET) reaction. Indeed, as in other ET-based assays (i.e., the frequently used DPPH assay), it gives an overview of the antioxidant activity exerted by all the antioxidant compounds, which operate through the transfer of an electron [43]. Figure 5 shows its value at T0, immediately after the process. As a result of the PEF process, total polyphenol content was noted to be preserved and even enhanced (UJ: 858.04 \(\pm\) 5.27 mg gallic acid equivalent (GAE)/L; PEFJ: 867.77 \(\pm\) 0.63 mg GAE/L). In previous studies, comparable values were reported with respect to total phenolic contents for untreated and PEF-treated orange juice [16]. Similarly, the application of PEF treatment (40 kV/cm, 130 \(\upmu\)s) to an orange juice-milk beverage caused a 9% increase in total phenolics [44]. These results are also in accordance with what was reported by [19], who reported that the radical scavenging capacity, determined by DPPH, remained constant after PEF treatment (35 KV/cm, total treatment time equal to 1000 \(\upmu\)s) in orange juice samples. To the best of our knowledge, this is the first study reporting ORAC unit values for PEF-treated blood orange juice. The ORAC assay is based on a hydrogen atom transfer (HAT) reaction mechanism and measures the antioxidant scavenging activity against peroxyl radicals induced by AAPH radicals. Therefore, differently from the FCR assay, it is mainly correlated with those compounds that exert their antioxidant activity based on the transfer of a hydrogen atom. In the evaluation of the antioxidant activity of a food sample, it is essential to include at least one assay based on an ET reaction mechanism and one based on an HAT mechanism. Our results highlighted that ORAC unit values were significantly (\(p\leq\) 0.05) improved after PEF treatment. UJ had ORAC units equal to 3079.20 \(\pm\) 57.21, while PEFJ at T0 recorded 3398.87 \(\pm\) 31.71 ORAC units. This could be attributable to the fact that the electroporation phenomenon and the correlated increased permeabilization of the juice cells enhance the release of intracellular metabolites, thereby increasing mass transfer of antioxidant compounds out of the cells [16]. The trends recorded for total polyphenols and ORAC units during 20 days of refrigerated storage are reported in Table 3. As the refrigerated storage proceeded, total polyphenol content showed a gradual decline starting from 15 days, with the lowest values, equal to 836.16 \(\pm\) 0.80 mg GAE/L, being recorded after 20 days at the end of the refrigerated storage period. Our results are in accordance with what was previously reported by other authors [16], who showed that, during the shelf-life of PEF-treated orange juice, total polyphenol content decreased with the storage period. Regarding ORAC units, the retention of the antioxidant activity of PEFJ was recorded during the whole refrigerated storage period, as ORAC units were preserved and maintained until the end of the 20-day storage period. Indeed, PEFJ after 20 days still showed 3735 \(\pm\) 23.06 \(\upmu\)mol TE/100 mL as ORAC units, highlighting that the contribution of the bioactive components of the juice  
Figure 5: Total polyphenol content (**A**) and ORAC units (**B**) in UJ (untreated juice) and PEFJ (PEF-treated juice) immediately after the process (T0). Data are expressed as means of three analytical replicates \(\pm\) standard errors. Means’ significant differences are expressed by different letters: \(p\leq\) 0.05; \(n\) = 3. * GAE: Gallic acid equivalents. to the overall antioxidant capacity of the PEFJ was conserved. As previously reported, the relationship between the antioxidant activity and bioactive compounds depends on several factors, including the chemical structure of individual components, their synergistic interaction, and the specific conditions applied in different assays [43].