Modulating hydrophobic and antimicrobial gelatin-zein protein-based bilayer films by incorporating glycerol monolaurate and TiO2 nanoparticles

The hydrophobicity was developed on gelatin-zein bilayer films with enhanced antimicrobial properties and persistent inherent mechanical characterization by incorporating Glycerol monolaurate (GML) and nano-TiO₂. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) revealed that GML exhibited roughness and reduced porosity on outer zein surfaces, resulting in a water contact angle (WCA) > 90°. Substantial GML migration was also observed from gelatin film to acetic acid-containing zein layers and improved hydrophobicity. Conversely, nano-TiO₂-assisted hydrophilic porous microstructure indicated lower WCA, and nano-TiO₂ influenced the regulation of mechanical strength near controlled TS ( ≈ 20 MPa) with improved thermal resistance, whereas the extended flexibility (elongation >200 %) performed through GML incorporation. There were slight variations in water solubility (% WS) and moisture content (% MC), with 1 % (w/v) GML signifying better results in reducing water vapor permeability (WVP) and oxygen permeability (OP). Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) analysis also presented GML migration, altering crystalline structures and protein conformation. Using the bacterial inactivation model for the liquid medium, including the log-linear inactivation phase and tail, Gram-positive S. aureus ATCC29213 reached a maximum of around 2 log reduction, but Gram-negative E. coli JM109 showed higher resistance. Along with the surface-mediated effect, GML-incorporated gelatin layers and migrated GML also exhibited inactivation efficacy for bacterial exposure on the outer surface for a considerable time. Hence, GML and nano-TiO₂ synergistically hold promise for bioactive packaging with significant applications.