| Congresso Brasileiro de Microbiologia 2023 | Resumo: 329-2 | ||||
Resumo:Milk is an important source of substrates for bacterial growth and enterotoxin production. This food can be contaminated on the farm or in the industry by multiresistant opportunistic pathogens, such as Staphylococcus aureus (S. aureus). Therefore, innovative food processing technologies are being developed to reduce microbiological contamination and increase food safety. Among non-thermal techniques, Photodynamic Inactivation of Microorganisms (PDIM) stands out for not requiring high investments in equipment and specialized labor, requiring only a photosensitizer (PS) and a photon of visible light at an appropriate wavelength. This study aimed to photoinactivate S. aureus ATCC 25923 in fluid milk using Curcumin (CUR; 1, 7-bis-(4-hydroxy-3-methoxyphenyl)-1, 6-heptadiene-3, 5-dione) as a PS. For this purpose, sterile 10% reconstituted skimmed milk with CUR at concentrations of 250, 125 and 62.5 μg/mL was prepared. The strain was standardized by the McFarland 0.5 scale, which corresponds to 1.0 x 108 CFU/mL and inoculated at a rate of 10%, resulting in 1.0 x 107 CFU/mL. The samples remained refrigerated (7°C) in the dark for 10 min and were illuminated for 5 min with a blue light emitting diode device (λmax = 450 nm), resulting in a total energy dose of 0.81 cm-2. Milk was irradiated in the absence of PS to control the effect of light. PS samples were tested without light to control the antimicrobial activity of CUR in the dark. Serial decimal dilutions were inoculated onto Mannitol Salt Agar plates for cell viability counting. Plates were incubated at 37°C/48 h and results expressed in log CFU/mL. There was a significant difference (P<0.0001) for PDIM in cell viability. Light did not photoinactivate bacteria in the absence of PS. Light samples showed lower means (6.1 ± 0.5 log CFU/mL) when compared to dark samples (6.7 ± 0.5 log CFU/mL). Cell death occurs by the transfer of energy from the PS excited by the light photon to molecular oxygen, forming highly toxic reactive oxygen species (ROS) that cause nonspecific damage to bacteria. This mechanism of action acts on multiple targets, ensuring rapid and irreversible apoptosis, preventing the possibility of resistance development by microorganisms. However, the efficiency of the PDIM technique in milk may have been impaired by the optical density of the liquid that limits the penetration of blue light, composition of nutrients that affect the quantum yield of ROS and natural antioxidants present in the biological medium. The inhibition of microorganisms was proportional to the PS inclusion level. The most efficient treatment was CUR-illuminated milk at the highest concentration (250 μg/mL), where 1.6 log CFU/mL of S. aureus was inhibited. The drug decreased cell viability even in the absence of light, demonstrating the antimicrobial property of CUR in the dark and showed a synergistic antimicrobial effect when associated with PDIM. Therefore, CUR-mediated PDIM is a promising alternative to control the microbial growth of S. aureus in milk and, consequently, increase quality and shelf life. Palavras-chave: food preservation, food safety, innovative food processing technologies, microbiological contamination, multiresistant opportunistic pathogens Agência de fomento:Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) | |||||