## 2 Results and Discussion
### Antioxidant Components and Antioxidant Activity Assays
#### 2.2.1 Antioxidant Components
Means significant differences are expressed by different letters: \(p\leq\) 0.05; \(n\) = 3.  
never be below 60 mg/day [35]. Therefore, a retention of ascorbic acid after the industrial stabilization of freshly squeezed citrus juice is highly welcome and recommended. The herein proposed PEF process guaranteed a full retention of ascorbic acid content, as its value was equal to 62.92 \(\pm\) 4.82 mg/100 mL in PEF) at T0, immediately after the process. Several previous studies have reported very promising results for the PEF technology regarding the retention of ascorbic acid. Preservation of ascorbic acid in orange juice was reported by other authors [36] after low-energy PEF processing with 80 KV/cm and 0.333 Hz. Additionally, other authors [37] reported that PEF processing did not significantly change the concentration of ascorbic acid, which was equal to 55 mg/100 mL in both freshly squeezed orange juice and PEF-treated (40 KV/cm, 2.6 pulse duration time, and 97 ms total PEF treatment time) orange juice. [PERSON] et al. [14] reported 93% ascorbic acid retention after a PEF treatment of 35 KV/cm for 1000 us with bipolar pulses of 4 us. It is widely known that ascorbic acid is vulnerable to enzyme-catalyzed oxidation, specifically ascorbate oxidase and peroxidase [38]; therefore, it may be hypothesized that the applied PEF treatment partially deactivated some of the enzymes responsible for ascorbic acid loss [14]. Furthermore, it must be stressed that very intense PEF settings have been reported to have negative effects on the vitamin C contents. Indeed, [PERSON] et al. [39] reported that vitamin C values decreased with longer times and stronger fields (5-40 KV/cm, 30-340 us). Additionally, ref. [18] reported that the increased intensity of the PEF enhanced ascorbic acid degradation. Ascorbic acid is a heat-sensitive nutrient, and it is highly recommended to prevent the onset of high temperatures during citrus juice stabilization in order to avoid thermal damage. The application of high intensity fields is associated with the significant increase in the juice temperature during PEF processing, and this is probably the cause of the degradation of ascorbic acid that occurred while operating under stronger fields. As mentioned before, our PEF process conditions prevent thermal damage to the nutritional quality of blood orange juice, thereby ensuring the preservation of its high nutritional value. Total anthocyanin content significantly (\(p\leq 0.01\)) increased after our PEF process, changing from 52.35 \(\pm\) 0.04 mg cyanidin-3-glucoside equivalents (CGE)/L to 55.59 \(\pm\) 0.11 mg CGE/L (Figure 4). The anthocyanin content of blood orange juice is a very relevant quality characteristic that influences consumer acceptance. Indeed, the presence of anthocyanins is responsible for the brilliant red color of blood orange juice, along with being associated with a higher antioxidant efficiency of the juice [4]. In a previous study [40], it was demonstrated that fruit juice beverages treated in a low electric field (20 kV/cm) recorded higher total anthocyanin contents with respect to the untreated control samples, while higher electric  
Figure 4: Ascorbic acid (**A**) and total anthocyanin (**B**) contents in UJ (untreated juice) and PEJ (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: \(p\leq\) 0.01; \(n\) = 3.  
fields (40 kV/cm) led to anthocyanin degradation. The authors concluded that, at lower PEF conditions, the electroporation may enhance the extractability of anthocyanins from fruit cells and that the application of higher electric fields was detrimental due to the thermal damage induced in the beverage. In order to prevent degradation of bioactives, if higher PEF conditions have to be applied, they promoted the addition of antioxidant ingredients (i.e., stevia sweetener), thereby protecting the bioactive compounds of the juice from degradation.