Abstract

The inactivation effect of curcumin-mediated photodynamic technology (PDT), a novel alternative nonthermal technique, on Salmonella typhimurium (S. typhimurium) biofilm and its preliminary bactericidal mechanism and application in milk were investigated. Biofilm formed from S. typhimurium ATCC 14028 was incubated with the photosensitizer curcumin, followed by exposure to blue laser (mad450nm) for testing antibiofilm effect. Planktonic S. typhimurium was taken for exploring the possible bactericidal mechanism. After curcumin-PDT treatment, the damages of bacterial DNA and protein were observed by agarose gel electrophoresis and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) respectively, and the morphology change was visualized by scanning electron microscopy (SEM). Confocal laser scanning microscopy (CLSM) was employed to test bacterial membrane permeability change. Bacterial and biofilm culture and curcumin-PDT preparation were conducted in a microbial laboratory, and during the PDT processing, all samples were illuminated in an optical laboratory. All experiments were completed in the Department of Food Science and Engineering of Jinan University, China from 2019 to 2020. Bacterial viability decreased significantly when curcumin concentration and illumination time increased. Curcumin (80μM) combined with blue light (200mW/cm2) illumination for 20min inactivated more than 2lg/(CFU/mL) S. typhimurium biofilm. DNA damage, protein degradation, and morphological change of PDT-treated S. typhimurium were observed. Curcumin-PDT treatment gained less bactericidal effect on S. typhimurium in milk and the inactivation efficacy was related to type of milk, curcumin concentration, illuminated liquid level and liquid transmittance. Therefore, curcumin-PDT is a promising method or assistance to control foodborne S. typhimurium in milk, but further investigations should be conducted to illustrate how the milk compositions interact with curcumin and light and how milk nutrients and sensory attributes response to curcumin-PDT treatment.

Keywords: Photodynamic technology; Curcumin; Salmonella typhimurium; Biofilm; Milk