Antimicrobial photodynamic inactivation with curcumin against Staphylococcus saprophyticus, in vitro and on fresh dough sheet

Photodynamic inactivation (PDI), as a new non-thermal decontamination and preservation technology, exhibits the advantages of low cost, free of residue and non-microbial resistance. Curcumin (CUR) as a natural photosensitizer could effectively inactivate food spoilage bacteria at an absorbance wavelength (420–470 nm) light illumination. In this study, the in vitro influence of PDI process parameters on the inactivation of Staphylococcus saprophyticus and the antimicrobial mechanism was analyzed. Approximate 5 log CFU/ml reduction was obtained when treated with 25 μM CUR and 4.32 J/cm 2 of blue LED. Obvious cell wrinkles, cell membrane disruption, intracellular contents leakage and increased membrane permeability of S. saprophyticus cell were observed after CUR-PDI treatment. Further, generation of intracellular reactive oxygen species, along with decreased intracellular enzyme activities and increased degree of cell membrane depolarization verified cell damage. The in vivo photo-antibacterial effect (1.04 log CFU/g and 0.81 log CFU/g) was validated on fresh millet dough sheet at two initial bacterial loads (5 log CFU/g and 3 log CFU/g, respectively). These findings illustrated that CUR mediated PDI could be applied to inhibit S. saprophyticus growth and possibly prevent spoilage of fresh dough products.