Advancing quantification methods for polyphenols in brown seaweeds—applying a selective qNMR method compared with the TPC assay

Abstract

Introduction: Brown seaweeds are a sustainable biomass with a potential for various industrial applications. Polyphenols are an important contributor to this potential.Objective: The aim was total quantification of polyphenols in brown seaweeds from different tidal zones, using a selective 1 H quantitative NMR (qNMR) method, comparing the results with the colorimetric Folin-Ciocalteu total phenolic content (TPC) assay.Method: qNMR was performed with integration of selected peaks in the aromatic region (7-5.5 ppm). Deselection of non-polyphenolic 1 H signals was based on information from 2D ( 1 H-13 C, 1 H-15 N) NMR spectra. 13 C NMR phlorotannin characterisation facilitated the average number of protons expected to be found per aromatic ring used for the 1 H quantification.Results: Selective qNMR and the TPC assay showed similar results for the three sublittoral growing species from the Laminariaceae; lower amounts for Laminaria hyperborea and Laminaria digitata (qNMR: 0.4%-0.6%; TPC: 0.6%-0.8%, phloroglucinol equivalents (PGE), dry weight (DW)) and higher amounts for Saccharina latissima (qNMR: 1.2%; TPC: 1.5%, PGE, DW). For the eulittoral Fucaceae, Fucus vesiculosus (qNMR: 1.1%; TPC: 4.1%; PGE, DW) and Ascophyllum nodosum (qNMR: 0.9%; TPC: 2.0%; PGE, DW), the TPC results were found to be up to three times higher than the qNMR results. The 13 C NMR characterisation showed the highest phlorotannin polymerisation degree for F. vesiculosus. Conclusion:The TPC assay provided similar polyphenolic amounts to the selective qNMR method for sublittoral species. For eulittoral growing species, the TPC method showed amounts up to three times higher than the qNMR method-most likely illustrating the lack of selectivity in the TPC assay.

First Insight into the Neuroprotective and Antibacterial Effects of Phlorotannins Isolated from the Cell Walls of Brown Algae Fucus vesiculosus and Pelvetia canaliculata

“…Thus, the distinct molecular size fractions (<1, 1–10, 10–100, and >100 kDa) of phlorotannins demonstrate high variability, depending on the species, geographical region, and thallus zone [ 10 ]. This fact and the absence of commercially available standards make the characterization of phlorotannin profiles a challenging problem [ 11 ], which in the most efficient way can be addressed by ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and nuclear magnetic resonance (NMR) techniques [ 12 , 13 ].…”

An Eco-Friendly Extraction and Purification Approach for Obtaining Active Ingredients for Cosmetics from Two Marine Brown Seaweeds

“…Unfortunately, both species of concern here, Ascophyllum nodosum and Halidrys siliquosa , do not produce the monomer phloroglucinol but rather polymerized phlorotannins, as already demonstrated by previous studies [ 15 , 25 , 67 ]. Although Wekre et al [ 68 ] demonstrated the possibility of 1 H NMR for quantifying polyphenols in brown algae, in our case, it was not possible to quantify phlorotannins in the two species studied. The 1 H NMR analysis thus allows us to detect the presence of phlorotannins by signals present between 5.5 and 6.5 ppm, and to deduce the relative proportion of phlorotannins in the sample, visible by the height and the form of the signals, which agree with the contents of phenolic compounds determined by the colorimetric test (Folin–Ciocalteu procedure).…”

Evaluation of the antioxidant potential of brown seaweeds extracted by different solvents and characterization of their phenolic compounds by LC–ESI‐QTOF–MS/MS

“…From another perspective of marine geography, based on the investigations by Wekre et al. (2022), seaweed species thriving in shallower waters, like Ascophyllum sp. and Fucus sp., exhibited higher inherent concentrations of polyphenols compared to those found in the sublittoral zone, which might bring bias in the solvent efficiency.…”