Structure-function relationship in nano ZnO-curcumin reinforced pea protein films prepared via high-pressure...

The design of sustainable, active packaging materials offers a promising alternative to petroleum-based plastics. This study investigated the integration of zinc oxide nanoparticles (ZnO NPs) and curcumin (Cur) into pea protein isolate (PPI) films using high-pressure homogenization (HPH) to enhance structural and functional performance. ZnO NPs were synthesized via ultrasound-assisted precipitation, and curcumin was added at 0.075-0.375%. HPH treatment promoted uniform dispersion and improved film cohesion. HPH-treated films exhibited enhanced crystallinity, mechanical strength (tensile strength up to 1.94 MPa), and flexibility (up to 50.97%). Importantly, HPH reduced water vapor permeability (WVP), and the Cur-nZnO films showed the lowest WVP (3.9 ± 0.3 × 10^-10 g·m/(m²·s·Pa)) compared with HPH-treated and control films, indicating improved moisture barrier performance. Thermal stability improved with a higher degradation onset and residual mass due to the thermal resistance of ZnO. Optical analysis revealed that Cur-ZnO NPs films had the lowest UV-Vis transmittance, supporting their UV-blocking capability. Bioactivity assessments confirmed that Cur-ZnO NPs films achieved 1.3-1.6 log CFU/mL reductions in bacterial counts against Listeria innocua and Escherichia coli. Surface analysis via XPS confirmed successful integration of Cur and ZnO, with enrichment in oxygenated and zinc-related groups. Release studies in ethanol, acetic acid, and oleic acid revealed simulant-dependent kinetics. Cur followed the Peleg model behavior, with the highest release in acetic acid. Zn²⁺ release fit a zero-order model in ethanol, and diffusion was faster in acid. These results demonstrate the potential of HPH-processed Cur-ZnO NPs PPI films for active packaging, offering tailored barrier and antimicrobial functions.