Identification, Quantification, and Antioxidant Evaluation of Phenolic Compounds from Colored Opuntia ficus-indica (L.) Roots Using UHPLC-DAD-ESI-MS/MS

This study investigates the phenolic composition and antioxidant potential of root extracts from three Opuntia ficus-indica varieties (green, red, and orange) using ultra-high-performance liquid chromatography coupled with diode array detection and electrospray ionization–tandem mass spectrometry (UHPLC-DAD-ESI-MS/MS). Phenolic compounds were extracted with a hydromethanolic solvent and quantified by spectrophotometric assays, while antioxidant activity was assessed through DPPH, ABTS, iron III reduction, hydroxyl radical, and nitric oxide scavenging methods. A total of 26 compounds were identified, including piscidic acid, epicatechin-3-O-gallate, and isovitexin, with several phenolics newly reported for O. ficus-indica roots. The green and red varieties showed the highest phenolic contents (up to 147.82 mg/g extract) and strong antioxidant capacity, particularly in ABTS (IC50 = 29.38 μg/mL) and hydroxyl radical inhibition (>90%). Relative Antioxidant Capacity Index (RACI) analysis confirmed a consistent correlation between phenolic/flavonoid content and antioxidant efficacy. These findings highlight the analytical relevance of UHPLC-DAD-ESI-MS/MS for profiling underutilized plant matrices and support the potential use of O. ficus-indica root extracts as natural sources of bioactive compounds for pharmaceutical and biomedical applications.