Comparative evaluation of encapsulation efficiency, controlled release and antibacterial activity of edible nanoformulations against enteropathogens

Nanoencapsulation is an effective strategy to enhance the stability, delivery efficiency and biological activity of bioactive compounds. In the present study, three edible nanoformulations—chitosan nanoparticles, thymol-loaded lipid nanoparticles, and zein protein nanoparticles—were developed and evaluated for their encapsulation efficiency, release characteristics, and antibacterial activity against selected enteropathogenic bacteria. Encapsulation efficiency was determined using UV–visible spectrophotometry by quantifying the unencapsulated bioactive compound present in the supernatant. The results showed clear variations among the nanoformulations. Chitosan nanoparticles exhibited an absorbance of 0.501, corresponding to 24.8 µg/mL of free compound (0.62 mg), whereas thymol-loaded lipid nanoparticles showed a lower absorbance of 0.253 corresponding to 12.4 µg/mL (0.31 mg). Zein nanoparticles showed an intermediate absorbance of 0.389, corresponding to 19.2 µg/mL (0.48 mg). Based on these values, the encapsulation efficiency was calculated as 87.6% for chitosan nanoparticles, 90.4% for zein nanoparticles, and 93.8% for lipid nanoparticles, indicating that lipid nanoparticles provided the most efficient encapsulation system. The in vitro release study conducted over 24 h demonstrated differences in release behaviour among the formulations. Chitosan nanoparticles released 19.4% of the compound at 1 h and reached 100% cumulative release (2.07 mg) after 24 h. Lipid nanoparticles exhibited a faster release pattern, showing 23.3% release at 1 h and achieving 100% release (2.21 mg) after 24 h. In contrast, zein nanoparticles showed a relatively slower release profile with 19.8% release at 1 h and 100% release (1.67 mg) at 24 h, indicating a more controlled release behaviour. The antibacterial activity of the nanoformulations was evaluated using the agar well diffusion method against Escherichia coli MTCC 443, Salmonella typhi MTCC 733 and Shigella flexneri MTCC 1457. Lipid nanoparticles exhibited stronger antibacterial activity with inhibition zones of 14 ± 0.4 mm against E. coli, 12 ± 0.5 mm against S. typhi, and 14 ± 0.4 mm against S. flexneri, which were comparable to the standard antibiotic ciprofloxacin (15 ± 0.6 mm, 12 ± 0.5 mm, and 13 ± 0.4 mm, respectively). Chitosan nanoparticles produced inhibition zones of 8 ± 0.5 mm, 11 ± 0.4 mm, and 10 ± 0.3 mm, while protein nanoparticles showed 7 ± 0.3 mm, 10 ± 0.3 mm, and 11 ± 0.2 mm against the respective pathogens. Furthermore, lipid nanoparticles demonstrated a concentration-dependent antibacterial effect, where inhibition zones increased from 4 ± 0.5 mm at 125 µg/mL to 16 ± 0.5 mm at 1000 µg/mL for E. coli, 3 ± 0.3 mm to 15 ± 0.6 mm for S. typhi and 3 ± 0.4 mm to 16 ± 0.4 mm for S. flexneri. The results indicate that lipid nanoparticles exhibited superior encapsulation efficiency, faster release kinetics and stronger antibacterial activity compared with chitosan and zein nanoparticle systems. These findings highlight the potential of lipid-based edible nanoformulations as efficient antimicrobial nanocarriers for applications in food preservation, pharmaceutical formulations and nutraceutical products.