Rosmarinic acid from beach waste: Isolation and HPLC quantification in Zostera detritus from Arcachon lagoon

Detritus of Zostera noltii and Zostera marina collected from the beaches of Arcachon lagoon (France) over a 30-month period were screened as a new source of rosmarinic acid (RA), a phenolic acid and an economically important metabolite. The seasonal variation of the RA content was quantified in methanolic crude extracts using high-performance liquid chromatography. Concentrations of RA ranged from 2.2 to 18.0 mg g⁻¹ (dw) for Z. noltii and 1.3 to 11.2 mg g⁻¹ (dw) for Z. marina. This is the first time RA has been isolated from Z. noltii; detrital leaves of Zostera have never before been screened for their bioactive substances. The high RA content of Zostera flotsam is of interest for both the cosmetic and herbal industries. These results show that there is a real potential for harvesting beachcast Zostera.