Antioxidant Evaluation of Extracts from the Peel of the Prickly Pear Cactus <i>Opuntia</i><i> </i><i>streptacantha</i>

The species Opuntia streptacantha, commonly known as the cardon cactus, belongs to the Cactaceae family of plants. The fruit is known as tuna, and its pulp provides carbohydrates, proteins, dietary fiber, and minerals. The peel is a rich source of antioxidant compounds, including phenolics, flavonoids, and betalains, which have been demonstrated to possess beneficial properties for human health. The objective of this study was to extract compounds from the peel of Opuntia streptacantha, or prickly pear cactus, and evaluate their antioxidant capacity. Two extractions were conducted, one with water and the other with 60% water-ethanol, resulting in total solids yields of 4.0% and 5.3%, respectively. The ethanol extraction resulted in a higher concentration of phenolic compounds and antioxidant capacity, as evidenced by the total phenol yield of 19.98 mg gallic acid equivalents (GAE/g), flavonoid yield of 14.72 mg catechin equivalents (CE/g), and betalain yields of 0.77 mg betanin/g and 0.58 mg indicaxanthin/g. The antioxidant capacity was determined by the mean maximum effective concentration (EC50 μg/mL), with the following results: H₂O₂ = 1,141.0 ± 28.21 µg/mL, ROO- = no reaction, NO- = 87.0 ± 9.5 µg/mL, OH- = 1,017.0 ± 135.1 µg/mL, O₂ - = 26.88 ± 2.49 µg/mL, HCIO = 1,731 ± 51.2 µg/mL. The prickly pear peel extract was found to contain a number of compounds, including phenolic acids such as caffeic acid (5.53 mg/100g) and 3,4-dihydroxybenzoic acid (1.81 mg/100g), as well as flavonoids such as isorhamnetin 3-rutinoside (94). Additionally, the extract contains 0.07 mg/100 g of isorhamnetin, 47.69 mg/100 g of rutin, and 0.94 mg/100 g of quercetin. It also comprises betalains, including betanin (12.30 mg/100 g) and isobetanin (16.34 mg/100 g).