Assessing the photodynamic efficacy of different photosensitizer-light treatments against foodborne bacteria based on the number of absorbed photons.

Abstract

Increasing interests in photodynamic treatment (PDT) for food preservation require a holistic method to evaluate and compare different photosensitizer (PS)-light treatments. In this report, the absorbed photons were used as the basis to assess the antimicrobial photodynamic efficacy of two PSs, chlorophyllin sodium magnesium salt (Chl-Mg) and chlorophyllin sodium copper salt (Chl-Cu), under blue and white light against two typical foodborne pathogens, Gram-negative Escherichia coli, and Gram-positive Staphylococcus aureus. The results showed that the phototoxicity of a PS was predominantly decided by the absorbed photons rather than the characteristics of light sources. Photosensitized Chl-Mg exhibited superior antimicrobial activity as compared to that of ChlCu. The applied treatments were found to be more effective against S. aureus than E. coli. Bacterial inactivation kinetics as a function of the number of absorbed photons could be described by Weibull model with R2 from 0.947-0.962, and kinetics constants D in the range of 0.202\xa0×\xa01017 photons/cm2-2.409\xa0×\xa01018 photons/cm2. The kinetics models may find promising applications in the design, assessment, and optimization of PDT processes.