Phytochemical Composition and Bioactivity of Different Fruit Parts of Opuntia robusta and Opuntia ficus-indica: Conventional Versus NADES-Based Extraction

Abstract

This study evaluated the extraction efficiency of two Natural Deep Eutectic Solvents (NADESs), glycerol–urea (1:1) and citric acid–sorbitol (1:2), for recovering phenolic compounds from the different parts of the fruit (pulp, seed-containing pulp, seeds, and peel) of Opuntia robusta and Opuntia ficus-indica in comparison with 50% methanol. Phytochemical profiling was performed using ultra-high-performance liquid chromatography–high-resolution mass spectrometry, alongside antioxidant and enzyme inhibition assessments (acetylcholinesterase, butyrylcholinesterase, tyrosinase, α-glucosidase, and α-amylase). Glycerol–urea performed similarly to methanol in extracting phenolic compounds with notable antioxidant properties. Peel extracts contained the highest levels of bioactive compounds, particularly phenolic acids (525.49 in O. robusta and 362.96 µg/gDW in O. ficus indica). Enzyme inhibition varied across species and fruit parts, with extracts from both species inhibiting all targeted enzymes. Notably, this study provides the first evidence of tyrosinase inhibitory activity in O. robusta, which exhibited the strongest inhibition. Overall, these results emphasize the potential of cactus fruit extracts, particularly from O. robusta, for valorization, and support the use of NADESs as a sustainable and medium for extracting antioxidant compounds. Furthermore, the potential of fruit peel as waste with nutraceutical applications was demonstrated.