UV Oxidation: Mechanistic Insights Using a Model System.

Damage to hair by UV radiation is relevant to most people, and for many, it is a major source of hair damage. The chemistry is complex, and studying all of the detailed reactions is extremely challenging. The objective of this work was to create a model system that allows for the study of one key mechanism involved in UV damage: the oxidation of tyrosine. A colloidal system to study the reactivity and chemistry of tyrosine was tracked by monitoring tyrosine decomposition and dityrosine formation by fluorescence spectroscopy. Experiments showed both the important role of oxygen in the decomposition of tyrosine and how the addition of redox metals such as iron can accelerate this decomposition. Finally, an antioxidant, butylated hydroxytoluene, was demonstrated to reduce this oxidation through the interception of reactive oxygen species. These findings suggested two possible strategies for reducing UV-induced radical damage to hair: removal of redox metals and addition of a radical scavenger to react with reactive oxygen species formed. The second strategy was confirmed by testing selected extracts from tea (Camellia sinensis), which is well known to have antioxidant properties. An oxygen radical antioxidant capacity assay was used as a screening tool to identify which tea extracts have the highest antioxidant efficacy, and these extracts were shown to reduce UV-induced protein damage in hair. [ABSTRACT FROM AUTHOR]