Fenton discoloration of ultrasonicated purple cactus pear juice.

The aim of this study was to evaluate the stability of color, betaxanthin, and betacyanin pigments in the presence of Cu(II)-dependent hydroxyl radicals (HO?) from ultrasonicated purple cactus pear juice at amplitudes of 40%, 60%, and 80%, in comparison to untreated sample. L* parameter of juice treated at 40% and 80% amplitude for 25 and 15 min, respectively (11.3 and 9.3, respectively), were significantly higher compared to the control; b* and hue parameters of juice treated at 80%, 25 min showed values of 1.7 and 0.1, respectively. Color differences (?E) were lower (<3) for juices treated at high amplitude (80%) and short times (3?5 min). Juice treated at 40% 15 min, 60% 25 min, 80% 15 and 25 min presented high values of betacyanins (281.7 mgL?1, 255.9 mgL?1, 294.4 mgL?1, and 276.7 mgL?1, respectively). Betaxanthin values were higher in the juices treated at 40% 5 min and 80% 15 and 25 min (154.2 mgL?1, 135.2 mgL?1, and 128.5 mgL?1, respectively). Purple cactus pear juice exhibited significant chelating activity of copper ions and great stability when exposed to HO?.