Photodynamic inactivation of planktonic Staphylococcus aureus by sodium magnesium chlorophyllin and its effect on the storage quality of lettuce

Photodynamic inactivation (PDI) is a fast and effective non-heat sterilization technology. This study established an efficient blue light-emitting diode (LED) PDI with the photosensitizer sodium magnesium chlorophyllin (SMC) to eradicate Staphylococcus aureus in food. The antibacterial mechanisms were determined by evaluating DNA integrity, protein changes, morphological alteration, and the potency of PDI to eradicate S. aureus on lettuce was evaluated. Results showed that planktonic S. aureus could not be clearly observed on the medium after treatment with 5.0 μmol/L SMC for 10 min (1.14 J/cm2). Bacterial cell DNA and protein were susceptible to SMC-mediated PDI, and cell membranes were found to be disrupted. Moreover, SMC-mediated PDI effectively reduced 8.31 log CFU/mL of S. aureus on lettuce under 6.84 J/cm2 radiant exposure (30 min) with 100 μmol/L SMC, and PDI displayed a potent ability to restrain the weight loss as well as retard the changes of color difference of the lettuce during 7 day storage. The study will enrich our understanding of the inactivation of S. aureus by PDI, allowing for the development of improved strategies to eliminate bacteria in the food industry.