Incorporation of antibacterial zein/thymol nanoparticles dispersed using nanobubble technology improves the functional performance of gelatin films

In this study, the thymol-loaded zein nanoparticles (ZT-NPs) as a nanofiller were used to improve the antibacterial performance and extensibility of gelatin (GA) films. The air nanobubble water (NBW) treatment, a green technology, was employed to inhibit the agglomeration of ZT-NPs in the film to further improve those functional performances. The reinforcing role of NBW-treated ZT-NPs on the functional properties of the GA matrix as well as the mechanism of interaction between nanobubbles and ZT-NPs was studied at different concentrations. The results showed that NBW-treated ZT-NPs assembled into spherical shapes with mean diameters of 228 nm. The broken nanobubble induced the conformation change of zein and increased the number of hydrophilic groups. The remaining un-burst nanobubbles effectively adhered to ZT-NPs and caused a high dispersion of ZT-NPs in GA films. FTIR spectroscopic and DSC revealed an increase in hydrogen bonds and electrostatic interaction formed between GA and the NBW-treated ZT-NPs. Upon the addition of NBW-treated ZT-NPs (37.5%), the water vapor permeability increased by 20%, the elongation at break increased by 61.59%, and the thermal stability, as well as the opacity performance, had improved. Furthermore, the resulting N-G/ZT3 film showed excellent antimicrobial activities against Escherichia coli and Staphylococcus aureus. These results indicated that NBW treatment can be used in an industrial setting for the dispersion of ZT-NPs in GA films to effectively develop a flexible packaging with highly dispersed bio-fillers with improved antimicrobial activity.