Opuntia stricta (Haw.) Fruit Pulp and Seeds as Source of Bioactive Phytochemicals with Promising Functional Properties

In recent years, Opuntia stricta (Cactaceae family) has garnered considerable attention due to its promising nutritional and medicinal properties. This study aims to investigate the chemical composition and bioactivity of Sicilian Opuntia stricta fruit pulp and seeds. Liquid chromatography–mass spectrometry analysis revealed the presence of betalain derivatives, especially isobetanin and betanin, as the main pigments in the freeze-dried pulp and its hydroalcoholic extract. Other constituents, namely, piscidic acid, isorhamnetin-3-O-glucoside, and isorhamnetin-3-O-rutinoside, were identified. Linoleic acid (41.95%) was the main abundant fatty acid followed by palmitic acid (19.32%) in the seed’s fixed oil as analyzed by gas chromatography–mass spectrometry. The antioxidant activity was assessed using a multi-target approach using 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power assay (FRAP), and β-carotene bleaching tests. The ABTS test showed greater sensitivity to the action of the samples with significant half-maximal inhibitory concentrations (IC50) of 13.24 and 14.82 mg/mL for the hydroalcoholic extract and the freeze-dried fruit pulp, respectively. Opuntia stricta’s extracts were also assessed for the carbohydrate-hydrolyzing enzyme and lipase inhibitory effect. The freeze-dried fruit pulp exhibited the highest effect against lipase (IC50 of 33.54 μg/mL). Collectively, our results contribute to the characterization of this traditionally consumed Sicilian edible plant and suggest its use as a source of bioactive compounds useful for the prevention of obesity linked to hyperglycemia.