Ohmic heating-assisted synthesis of chlorophyll-sensitized TiO2 for enhanced visible light-driven photocatalytic antimicrobial activity

Abstract

Visible light-driven (VLD) photocatalytic inactivation has emerged as a promising approach to disinfection of foodborne pathogens due to its safety and eco-friendliness. Titanium dioxide (TiO₂), despite its widespread use as a photocatalyst, is limited in VLD applications because of its wide bandgap and rapid electron–hole recombination. To overcome these limitations, we propose a novel sensitization strategy using ohmic heating (OH) at 60 Hz to functionalize TiO₂ with the natural pigment chlorophyll. The optimal sensitization conditions were identified as 50 °C and 3.36 wt% chlorophyll loading. Chlorophyll-sensitized TiO₂ (Chl-TiO₂) prepared via OH exhibited a 2 log CFU/mL higher inactivation of Staphylococcus aureus and Listeria monocytogenes in phosphate-buffered saline under visible light (> 400 nm) irradiation for 1 h (62.52 J/cm²) compared to conventional heating-assisted Chl-TiO₂ nanoparticles. The enhanced antimicrobial activity of OH-assisted Chl-TiO₂ was associated with increased membrane damage, lipid peroxidation, DNA damage, and elevated intracellular reactive oxygen species (ROS) generation. Nanoparticle characterization further revealed greater chlorophyll adsorption in OH-assisted Chl-TiO₂. This enhanced chlorophyll loading contributed to improved photocatalytic properties through stronger hole oxidation potential and suppressed electron–hole recombination. Furthermore, the OH-assisted Chl-TiO₂ was incorporated into carrageenan-based nanocomposite films to evaluate their potential for industrial applications. The combination of optimized film and 4 h (250.08 J/cm²) of visible light exposure inactivated S. aureus and L. monocytogenes on cantaloupe surfaces by up to 1.80 and 1.88 log CFU/g, respectively. These films demonstrated enhanced antimicrobial activity and improved mechanical properties. These findings highlight the potential of OH-assisted Chl-TiO₂ nanocomposite films in packaging materials for the preservation of fresh produce.