Photodynamic antimicrobial decontamination of food packaging using a chitosan-Zn(II) protoporphyrin IX conjugate

Abstract

Effective decontamination methods are vital to minimizing the presence of harmful microorganisms in fresh foods. The use of bioactive compounds in packaging processes is one of the most suitable methods to preserve food quality and improve food safety. In this study, Zn(II) protoporphyrin IX was linked to chitosan to obtain a conjugate CS-ZnPPIX. The objective was to develop a naturally-based polymeric material capable of eliminate microbial contamination in food packaging through photodynamic inactivation of pathogens. The CS-ZnPPIX film displayed a homogeneous coating of the surfaces. The absorption and emission spectra of the conjugate exhibited typical Zn(II) porphyrin bands, along with a fluorescence quantum yield of 0.054. The photodynamic analysis revealed that CS-ZnPPIX was capable of generating singlet molecular oxygen (ΦΔ = 0.49) and superoxide anion radicals. In vitro experiments were conducted using the Gram-positive bacterium S. aureus. Upon exposure to 1 μM CS-ZnPPIX and 30 min of white light irradiation, the bacteria were effectively eradicated (> 7 log, 99.9999 % reduction in survival). Furthermore, the efficacy of PDI was assessed for reducing S. aureus contamination on food containers. The conjugate CS-ZnPPIX was effective in decontaminating polyethylene terephthalate, expanded polystyrene, glass, and aluminum packaging materials. Treatment of these bacteria-contaminated surfaces with 0.54 nmol CS-ZnPPIX resulted in a reduction in bacterial survival of more than 5 log (99.9998 %) after 30 min of irradiation. Furthermore, this procedure was effective in eliminating individual pathogen cells attached to surfaces. Therefore, the CS-ZnPPIX conjugate has suitable properties for decontaminating packaging, achieving aseptic materials, and aiding in food preservation.