Integrated Optimization of Opuntia stricta Extracts Coupled with HPLC-Based Phenolic Profiling: Linking Phytochemical Composition to Molecular Docking Simulation

This study intended to simultaneously model and optimize aqueous extracts obtained from whole Opuntia stricta fruits (OSE) to maximize the overall response profile, namely total phenolic content (TPC), total flavonoid content (TFC), antioxidant activity and antibacterial efficacy. For this purpose, the Response Surface Methodology was used to evaluate the influence of three extraction parameters: temperature, sample-to-solvent ratio, and time. Optimal extraction was predicted at 40 °C, 35.6 min, and a 1:50 (g/mL) ratio, yielding predicted TPC, TFC, ABTS IC50, and MIC values of 77.194 mg GAE/g, 3.787 mg CE/g, 0.187 mg/mL, 5.476 mg/mL, and 7.883 mg/mL, respectively. Experimental validation gave 77.23 mg GAE/g, 3.74 mg CE/g, 0.19 mg/mL, and MICs of 5 and 10 mg/mL against S. aureus and E. coli, respectively. Good agreement was observed between predicted and experimental values for most responses (relative errors: 0.05–9.52%), whereas anti-E. coli activity showed lower predictive accuracy, with a relative error of 21.17%. Principal component analysis (PCA) differentiated the various OSEs and revealed associations between their phytochemical composition and biological activities. High-performance liquid chromatography analysis of the optimized OSE revealed that 4-hydroxyphenylacetic acid was the predominant phenolic acid identified, while epicatechin was the major flavonoid detected. Molecular docking calculations revealed that catechin exhibited the most negative free energy of binding towards the studied virulence factors, including PPK (−8.2 Kcal/mol) and Fibronectin-binding protein A (−7.9 Kcal/mol) of E. coli and S. aureus, respectively. These findings indicate notable target interactions and highlight the bioactive potential of OSE, supporting further in vitro/in vivo validation and functional and industrial applications.