The key phytochemistry of rosemary (Salvia rosmarinus) contributing to hair protection against UV
Authors: Marsh Jennifer M. , Whitaker Shane , Li Lijuan , Fang Rui , Simmonds Monique S. J. , Vagkidis Nikolaos , Chechik Victor 
Published: July 2023

Extracts from rosemary (Salvia Rosmarinus) are analysed for their phytochemistry using LC–MS and the phytochemistry identified. The same extracts were tested for their efficacy to act as antioxidants by both hydrogen‐atom transfer (ORAC) and single electron transfer (FRAP). A correlation analysis was performed to identify the key phytochemistry responsible for antioxidant efficacy. The top performing extracts were then tested in a peptide model and in hair with the presence of UV to measure ability to protect against UV‐induced peptide and protein damage. Polyphenols (e.g. rosmarinic acid, glycosides of selgin) and abietane diterpenes (e.g. carnosic acid) in rosemary were identified as the principal compounds which enables the extracts to protect hair from UV.

Objective

The objective of this work was to correlate the phytochemistry of rosemary (Salvia rosmarinus), a botanical with known antioxidant properties, to a UV protection benefit in hair. These data will give insights into mechanisms of UV damage, the ROS formed and their reactivity.

Methods

LC–MS was used to compare the compounds in 10 commercial extracts of rosemary. ORAC (oxygen radical antioxidant capacity) and FRAP (ferric reducing antioxidant power) were used to measure the antioxidant capacity of the rosemary extracts. The ORAC assay measures ability of an antioxidant to react with a peroxyl radical via hydrogen atom extraction and FRAP measures electron transfer through reduction of ferric iron (Fe3+) to ferrous iron (Fe2+) by antioxidants present in the samples. Correlation of extract composition with antioxidant measures was performed using principal component analysis. Selected extracts were assessed for their ability to protect hair from UV damage in a model peptide system and on hair. In addition, the same methods were used to test rosmarinic acid and carnosic acid, key phytochemistries in the rosemary extracts. The model system was a peptide and its decomposition on exposure to UV was monitored by LC–MS in the absence and presence of the rosemary extracts. Hair degradation in the presence of UV was measured by exposure of UV in an Atlas weatherometer followed by extraction of degraded protein in water. A fragment of the S100A3 protein was used as a marker of UV damage (m/z = 1278) and quantified via LC–MS.

Results

Ten rosemary extracts were assessed for antioxidant performance and correlated with their compositions. The phytochemistry in each extract varied widely with a total of 33 individual compounds identified. The differences were most likely driven by the solvent and extraction method used by the supplier with extracts varying in the proportion of polar or non‐polar compounds. This did influence their reactivity in the ORAC and FRAP assays and their efficacy in preventing protein damage. Two of the key compounds identified were rosmarinic acid and carnosic acid, with rosmarinic acid dominating in extracts with mainly polar compounds and carnosic acid dominating in extracts with mainly nonpolar compounds. Extracts with higher rosmarinic acid correlated with ORAC and FRAP scores, with UV protection on hair and in the peptide model system. The extracts chosen for hair experiments showed hair protection. UV protection was also measured for rosmarinic and carnosic acid.

Conclusions

Despite the variation in the profile of phytochemistries in the 10 rosemary extracts, likely driven by the chosen extraction method, all rosemary extracts had antioxidant activity measured. This study suggests that the polyphenols (e.g. rosmarinic acid, glycosides of selgin) and abietane diterpenes (e.g. carnosic acid) are the principal compounds which enables the extracts to protect hair from UV.