## 3 Results
### Optical Properties of Red Pickly Pear Juice
Changes in antioxidant activity are mainly due to bioactive compound alterations of the fruit such as polyphenols, ascorbic acid, carotenoids, and pigments, among others, that  
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Treatment**}} & \multicolumn{6}{c}{**\(\Delta\)E: Compared to Untreated juice**} \\ \cline{2-9}  & \multicolumn{3}{c}{**pH 3.6**} & \multicolumn{3}{c}{**pH 7**} & \\ \cline{2-9}  & **Day 0** & **Day 5** & **Day 10** & **Day 20** & **Day 0** & **Day 5** & **Day 10** & **Day 20** \\ \hline Untreated juice (Control) & N/A & N/A & N/A & N/A & N/A & N/A & N/A & N/A \\ U-C (9.87 mJ/cm\({}^{2}\)) & 2.0 \(\pm\) 0.5\({}^{\circ}\) & 2.4 \(\pm\) 0.0\({}^{\circ}\) & 2.04 \(\pm\) 0.3\({}^{\circ}\) & 3.19 \(\pm\) 0.1 \({}^{\circ}\) & 3.6 \(\pm\) 0.2 \({}^{\circ}\) & 6.6 \(\pm\) 0.1 \({}^{\circ}\) & 11.8 \(\pm\) 0.0\({}^{\circ}\) & 23.1 \(\pm\) 0.6 \({}^{\circ}\) \\ U-C (15.13 mJ/cm\({}^{2}\)) & 2.8 \(\pm\) 0.0\({}^{\circ}\) & 2.6 \(\pm\) 0.1\({}^{\circ}\) & 2.03 \(\pm\) 0.0\({}^{\circ}\) & 3.09 \(\pm\) 0.2 \({}^{\circ}\) & 3.6 \(\pm\) 0.1\({}^{\circ}\) & 6.6 \(\pm\) 0.1 \({}^{\circ}\) & 12.3 \(\pm\) 0.0\({}^{\circ}\) & 20.0 \(\pm\) 0.2 \({}^{\circ}\) \\ U-C (31.78 mJ/cm\({}^{2}\)) & 3.4 \(\pm\) 0.6\({}^{\circ}\) & 3.4 \(\pm\) 0.1\({}^{\circ}\) & 2.79 \(\pm\) 0.0\({}^{\circ}\) & 3.19 \(\pm\) 0.1\({}^{\circ}\) & 4.0 \(\pm\) 0.2\({}^{\circ}\) & 7.3 \(\pm\) 0.1\({}^{\circ}\) & 10.7 \(\pm\) 0.0\({}^{\circ}\) & 21.7 \(\pm\) 0.3 \({}^{\circ}\) \\ HTST (80 \({}^{\circ}\)C) & 6.4 \(\pm\) 0.1\({}^{\circ}\) & 1.7 \(\pm\) 0.2\({}^{\circ}\) & 1.80 \(\pm\) 0.1\({}^{\circ}\) & 3.19 \(\pm\) 0.2\({}^{\circ}\) & N/A & N/A & N/A & N/A \\ UHT (130 \({}^{\circ}\)C) & N/A & N/A & N/A & N/A & 37.4 \(\pm\) 1.7\({}^{\circ}\) & 35.6 \(\pm\) 0.0\({}^{\circ}\) & 29.5 \(\pm\) 1.7\({}^{\circ}\) & 29.9 \(\pm\) 1.3\({}^{\circ}\) \\ \hline \multicolumn{1}{c}{**AE: Compared to Untreated juice, day 0**} \\ \cline{2-9}  & **Day 0** & **Day 5** & **Day 10** & **Day 20** & **Day 0** & **Day 5** & **Day 10** & **Day 20** \\ \hline Untreated juice (Control) & N/A & 1.4 \(\pm\) 0.5\({}^{\circ}\) & 1.5 \(\pm\) 0.1 \({}^{\circ}\) & 1.5 \(\pm\) 0.1 \({}^{\circ}\) & N/A & 2.0 \(\pm\) 0.0\({}^{\circ}\) & 3.8 \(\pm\) 0.2\({}^{\circ}\) & 4.4 \(\pm\) 0.0\({}^{\circ}\) \\ U-C (9.87 mJ/cm\({}^{2}\)) & 2.0 \(\pm\) 0.5\({}^{\circ}\) & 1.8 \(\pm\) 0.1\({}^{\circ}\) & 3.0 \(\pm\) 0.3\({}^{\circ}\) &  
can be affected by the processing. Although, in this study, the concentrations of polyphenols did not show noticeable changes due to the effects of the study variables, trends or changes in antioxidant activity can be attributed, in addition to the content, to the type of polyphenol and therefore on its structure [44] and the radical scavenging capacity of betalains, which could be reduced/increased depending on their structural features [2]. After processing, there was a reduction in the content of betacyanins and betaxanthins, and it has been reported that betalain degradation products may show enhanced antioxidant properties [4]. After storage under suitable conditions, betalains can be regenerated or have a change in structure [39], impacting the antioxidant activity. The changes observed in antioxidant activity at storage day five can be explained by the degradation and regeneration of betalains. There were no changes at storage times greater than five days. The UV-C doses applied did not show a significant difference (\(p>0.05\)) in the juices treated, presenting a decrease on day zero of 12.68 and 14.06% in juices at pH 3.6 (Figure 3a) and 7 (Figure 3b), respectively. Juices irradiated with the higher dose (31.78 mJ/cm\({}^{2}\)) in both pHs, and with storage day 20, they decreased antioxidant activities by 40% (pH 3.6) and 36.22% (pH 7). [PERSON] et al. [43] reported no significant difference (\(p>0.05\)) in antioxidant activity by UV-C dose (3.52 J/m\({}^{2}\)) at different irradiation times (15, 30, and 60 min).