Βeta-carotene protects sudan IV from photocatalytic degradation in a micellar model system: Insights into the antioxidant properties of the “golden” Staphylococcus aureus

Abstract

Sterilization using titanium dioxide-mediated photocatalysis has been shown to be a powerful biocidal process due to the production of reactive redox species (RRS). More specifically, these RRS generated from TiO₂ photocatalysis are able to completely oxidize organic material, including microorganisms. Photocatalysis is a potentially useful application for the production of u.v.-illuminated self-sterilizing surfaces such as in surgical suites or water purification. Some organisms are able to protect themselves from radicals and oxidants by producing carotenoid pigments which scavenge free radicals and oxidants. In this work we have created a micellar model with a target dye and used the model to demonstrate that when β-carotene is incorporated into the system it will protect the target dye from photocatalytic destruction. Our model will help to predict how difficult it will be to destroy microbes when exposed to photocatalysis. Our data showed that 50% of the target dye was protected after 5 min of photocatalytic oxidation when β-carotene was present in the micellar system. However, when the micellar system lacked β-carotene protection, 82% of the dye was destroyed via photocatalysis. As a frame of reference, we subjected our model system to standard oxidative Fenton conditions namely, Fe(NO₃)₃/H₂O₂. We demonstrated that after 90 min exposure to the above reagents 80% of the target dye remained when β-carotene was present in the micellar system. However, when no β-carotene was present 62% of the dye was destroyed under Fenton conditions.