Advancing quantification methods for polyphenols in brown seaweeds-applying a selective qNMR method compared with the...

Area of Science:

• Marine Botany
• Analytical Chemistry
• Biomass Valorization

Background:

• Brown seaweeds represent a sustainable biomass resource with significant industrial potential.
• Polyphenols are key compounds contributing to the value and applications of brown seaweeds.

Purpose of the Study:

• To quantify total polyphenols in brown seaweeds from various tidal zones.
• To compare results from a selective quantitative NMR (qNMR) method with the colorimetric Folin-Ciocalteu total phenolic content (TPC) assay.

Main Methods:

• Quantitative NMR (qNMR) utilized selective peak integration in the aromatic region (7-5.5 ppm).
• 2D NMR (¹H-¹³C, ¹H-¹⁵N) spectra were used to deselect non-polyphenolic ¹H signals.
• ¹³C NMR characterization of phlorotannins determined the average protons per aromatic ring for ¹H quantification.

Main Results:

• qNMR and TPC assays yielded similar polyphenol levels for sublittoral Laminariaceae species.
• For eulittoral Fucaceae species (Fucus vesiculosus, Ascophyllum nodosum), TPC results were up to three times higher than qNMR.
• ¹³C NMR indicated the highest phlorotannin polymerization degree in Fucus vesiculosus.

Conclusions:

• The TPC assay shows comparable polyphenol quantification to selective qNMR for sublittoral brown seaweeds.
• The TPC assay's lack of selectivity leads to overestimation of polyphenols in eulittoral species compared to qNMR.