Inativação fotodinâmica do microrganismo Staphylococcus aureus presente em leite cru e pasteurizado

Abstract

Over the past few years Photodynamic Therapy have been applied on multiple areas. One of these is the food disinfection through the Antimicrobial Photodynamic Therapy (aPDT) or Photodynamic Inactivation (PDI). Photodynamic Inactivation shows up as a strong alternative in controlling resistant pathogens agents, once the generated cytotoxic products act in a indiscriminate way to destroy celular structures. The mechanism of action of PDI occurs when a specific photosensitizer (PS) is excited by a light source in resonant wavelength with its absorption band, promoting the formation of reactive oxigen species that exhibit cytotoxic action against microorganisms. In this study, the PDI is presented as a mechanism of inactivation of the microorganism Staphylococcus aureus (S. aureus) present in the milk, using as PS a Curcumin salt (PDT Pharma – Cravinhos – SP), which is a natural PS and has been gaining ground in scientific researches. We used PDI to milk decontamination in two ways: raw and pasteurized. We divided our work in two investigations: a microbiological one, using aqueous solution of milk, and another one, varying the concentration of milk from 10% to 100%. In both steps we evaluated the efficacy of the technical monitoring the population of microorganism S. aureus, in loco, as a function of the concentrations of 750, 1500 and 3000 mg/L of PS. Our protocol consisted of 4 (four) groups: G1 (control: milk and S. aureus), G2 (milk, S. aureus and Curcumin), G3 (milk, S. aureus and light) and G4 (milk, S. aureus, Curcumin and light (PDI)). The light parameters were the powers of 30, 60 and 110 mW from a LED system in 450 nm (BioPSY-São Carlos-SP) and the exposure times from 5 to 30 minutes, which generated to us doses of 9, 18, 33, 54, 108 and 198 J/cm². The microbiological results obtained showed that the PS in concentration of 750 mg/L was extremely effective with doses of light of 33, 54, 108 and 198 J/cm², performing total inactivation of the S. aureus colonies when compared with control group, both for raw milk and to pasteurized milk. To understand the results with milk in concentrations from 10% to 100%, we performed measures of penetration depth of light in these samples and we draw isointensity curves, which allowed us to see that the milk behaves as a highly scattering medium, decreasing the light penetration as we increase its concentration. The results obtained with the protein content before and after PDI exhibited that proteic variation were minimal.