Antioxidant and anti-inflammatory activities of Opuntia ficus-indica L. extracts from different plant parts collected from two ecosystems in Northwestern Algeria: in vitro and DFT calculations studies

Opuntia ficus-indica L., a plant species that is commonly used in traditional medicine to treat diabetes, inflammation-related diseases, gastric ailments, and wounds on the skin, was studied for the first time. In this research, the phytochemistry, total phenolic compounds, in vitro antioxidant and anti-inflammatory capacity of the ethanolic extracts obtained from the cladodes, bark, and seeds of the plant collected from Mediterranean and Continental ecosystems are evaluated. The antioxidant and anti-inflammatory activities were further explained by DFT calculations. The phenolic acid derivatives, caffeic acid and ferulic acid, were studied to explain the structural dependency of the antioxidant activity of these compounds. In quantitative analysis, the results revealed that cladode ethanolic extract Mediterranean (CEEM), bark ethanolic extract continental (BEEC) and the seed ethanolic extract Mediterranean (SEEM) presented a high amount of total phenolic with a value of 177.33±2.01 μg gallic acid equivalent, 9.18±2.23 μg quercetin equivalent and 110.63±0.41 μg catechin equivalent/mg dry extract, respectively. Through the DPPH radical scavenging and reducing power assays, SEEM showed high in vitro antioxidant of the order of 0.08±0.00 and 1.03±0.03 mg/mL, respectively. Caffeic acid shows higher biological activity owing to higher HOMO energy (-6.0438 eV), higher softness 6.7536 Hartree-1, while a smaller value of the energy gap (4.0292 eV). Overall, the computational results indicate that both caffeic and ferulic acids are highly reactive antioxidants while caffeic acid appears to have a slightly stronger electron-donating ability. In conclusion, the O. ficus-indica fruit provides effective natural antioxidants for the patient, and may prove to have potential health benefits as natural antioxidant and anti-inflammatory agents.