Breaking acidic barriers and thermal defenses: Light-induced membrane disruption and heat synergy for efficient inactivation of Alicyclobacillus acidoterrestris in juice.

Light-responsive antimicrobial technologies, including photothermal (PT) and photodynamic (PD) treatments, have shown great promise in foodborne microbial control due to their green, residue-free nature. However, their efficacy in fruit juice is limited by Alicyclobacillus acidoterrestris (A. acidoterrestris, DSM 3922^T), which tolerates photothermal stress and thrives in acidic conditions that inhibit reactive oxygen species (ROS) generation by photosensitizers. To address these issues, we developed a composite material (MPDFE) combining a metal ion-enhanced acid-tolerant photosensitizer platform with a photothermal module. Erythrosine coordinated with Fe3+ forms a stable ROS-generating system under acidic conditions, which disrupts the bacterial cell membrane and compromises thermal resistance. Simultaneously, magnetic polydopamine nanoparticles provide mild localized photothermal effects (<63 °C), further enhancing bacterial inactivation. The material can be rapidly removed from juice via magnetic separation after treatment. Benefiting from the combined overcoming of acid inhibition and thermal tolerance, MPDFE achieves efficient inactivation of A. acidoterrestris (106 CFU/mL) in juice within 20 min, with significantly higher efficacy than photothermal treatment alone. The material shows good biosafety and recyclability, and has minimal impact on juice quality. This strategy provides a promising technical approach for mild and efficient sterilization of heat-sensitive juice products.