BIOACTIVE POTENTIAL OF FORAGE CACTUS EXTRACTS: ANTIOXIDANT AND ANTIMICROBIAL ACTIVITIES

Forage cactus, represented by species such as Opuntia and Nopalea, plays an important ecological and economic role in arid and semi-arid regions, including the Brazilian semi-arid zone. Rich in bioactive compounds—such as polyphenols, flavonoids, carotenoids, vitamins, and polyunsaturated fatty acids—it shows notable in vitro antioxidant and antimicrobial potential. This study assessed the bioactive potential of extracts from four forage cactus varieties (Sertânia, Elefante, Miúda, and Gigante), focusing on in vitro antioxidant and antimicrobial activities. Total phenolic content was determined by the Folin–Ciocalteu method; antioxidant activity was measured using FRAP and DPPH assays; and antimicrobial activity was evaluated by agar diffusion against Escherichia coli and Staphylococcus aureus. Analyses were performed in triplicate, using gallic acid and Trolox as standards. Miúda had the highest total phenolic content (14.84 ± 0.34 mg GAE/g), followed by Gigante (12.43 ± 0.26 mg GAE/g). Elefante and Sertânia showed the lowest values (< 4 mg GAE/g) and did not differ statistically from each other, while the other varieties differed significantly. In the FRAP assay, Miúda (3.90 ± 0.15 mMol/g) and Sertânia (3.44 ± 0.05 mMol/g) did not differ statistically, both showing the highest reducing capacities. Gigante also did not differ statistically from Elefante (1.18 ± 0.10 mMol/g and 0.60 ± 0.11 mMol/g, respectively). In the DPPH assay, Miúda (34.14 ± 0.04 mMol/g), Gigante (33.77 ± 0.08 mMol/g), and Elefante (33.40 ± 0.33 mMol/g) were statistically equal, all with high free radical scavenging capacity. This indicates that the chemical structure of the compounds present strongly influences antioxidant activity. Sertânia, despite high FRAP activity, had significantly lower DPPH performance (28.47 ± 0.07 mMol/g), highlighting the selectivity of antioxidants across different mechanisms. No inhibition halos were observed in antimicrobial tests; however, no bacterial growth occurred directly on sample surfaces, indicating antimicrobial action by contact. This may be linked to the low diffusibility of high molecular weight compounds, such as polysaccharides and complex phenolics. Overall, Miúda stood out for its high phenolic content and strong in vitro antioxidant activity in both FRAP and DPPH assays. Gigante also showed strong performance, with high phenolic content and excellent DPPH results. Sertânia, though low in phenolics, excelled in FRAP. These findings underscore confirm the potential of forage cactus as a promising source of functional substances.