NMR use to quantify phlorotannins: The case of Cystoseira tamariscifolia, a phloroglucinol-producing brown macroalga in Brittany (France)

• Phloroglucinol is quantified using qNMR in Cystoseira tamariscifolia.
• qNMR stands as an accurate phlorotannin quantification method.
• qNMR specificity is a key advantage for chemical ecology.

Among the most renowned natural products from brown algae, phlorotannins are phloroglucinol polymers that have been extensively studied, both for their biotechnological potential and their interest in chemical ecology. The accurate quantification of these compounds is a key point to understand their role as mediators of chemical defense. In recent years, the Folin–Ciocalteu assay has remained a classic protocol for phlorotannin quantification, even though it frequently leads to over-estimations. Furthermore, the quantification of the whole pool of phlorotannins may not be relevant in ecological surveys. In this study, we propose a rapid 1H qNMR method for the quantification of phlorotannins. We identified phloroglucinol as the main phenolic compound produced by the brown macroalga Cystoseira tamariscifolia. This monomer was detected in vivo using 1H HR-MAS spectroscopy. We quantified this molecule through 1H qNMR experiments using TSP as internal standard. The results are discussed by comparison with a standard Folin–Ciocalteu assay performed on purified extracts. The accuracy and simplicity of qNMR makes this method a good candidate as a standard phlorotannin assay.

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