Formulation and Optimization of Chitosan Nanocarriers Loaded With Ziziphora clinopodioides Lam. Essential Oil Using Response Surface Methodology: Improvement of Physical, Antioxidant, and Antibacterial Properties

This study aimed to optimize the functional and structural performance of Ziziphora clinopodioides essential oil (ZcEO)–loaded chitosan (CS) nanocarriers by evaluating the individual and interactive effects of different concentrations of CS, ZcEO, and TPP on antioxidant and antibacterial capacities, as well as Z ‐average and PDI, through response surface methodology. The Z ‐average values ranged from 116.17 to 4489 nm, and PDI values varied between 0.16 and 1.91. Increasing ZcEO concentration significantly reduced both Z ‐average and PDI values. CS at lower concentrations led to aggregation and the formation of larger, heterogeneous particles. Higher concentrations of TPP resulted in larger nanoparticles with higher PDI values, whereas optimal TPP levels enhanced structural integrity and increased antioxidant activity from 9.94% to 27.22%. Balanced concentrations of CS, TPP, and ZcEO improved antimicrobial efficacy, as evidenced by increased inhibition rates against Salmonella Typhimurium (from 87.01% to 92.23%) and Listeria monocytogenes (from 67.17% to 90.52%). The optimized formulation consisted of 4 mg/mL CS, 7.4 mg/mL ZcEO, and 4 mg/mL TPP, which produced nanoparticles of 30 nm with a PDI of 0.40, antioxidant activity of 25.10%, and strong antimicrobial efficacy. Furthermore, SEM confirmed a uniform spherical morphology and the successful entrapment of ZcEO within the polymeric matrix. These findings demonstrate a scalable and efficient methodology for nanoencapsulating EOs, establishing CS–TPP nanoparticles as effective bioactive carriers with improved physicochemical and functional properties.