Antimicrobial photodynamic efficacy of selected natural photosensitizers against food pathogens: Impacts and interrelationship of process parameters

Photodynamic treatment (PDT) could be a viable option to decontaminate food or food contact surfaces. Such applications require a rigorous method to assess the efficacy of different photosensitizer-light source systems. It is also essential to determine suitable treatment conditions to achieve desirable microbial inhibition for a given process. In this connection, we evaluated and compared the antimicrobial activity of two natural photosensitizers (aloe emodin, curcumin) under PDT based on the number of absorbed photons. The degree of bacterial inactivation was then correlated to the absorbed photons as well as the process parameters through kinetics study. The results showed that aloe emodin was more effective than curcumin against both S. aureus and E. coli when the number of absorbed photons was matched. Aloe emodin reduced about 2.3 log units of S. aureus and 1.1 log units of E. coli more than curcumin. E. coli was more resistant to PDT than S. aureus. Inactivation kinetics of S. aureus and E. coli as a function of the number of absorbed photons can be described by the Weibull model with D values of 1.296 x 10(17) photons/cm(2) and 2.446 x 10(18) photons/cm(2), R-2 of 0.969 and 0.968, respectively. The interrelationship between the concentration of photosensitizer, radiant fluence, and degree of bacterial inactivation could be used to determine and optimize treatment conditions of PDT processes.