A review of analytical techniques for characterizing phlorotannins in brown seaweeds: Current challenges and future prospects

Abstract

Phlorotannins, the polyphenols mostly found in brown seaweeds, have attracted high attention from the pharmaceutical industry in recent years due to their antioxidant, antibacterial, and anti-inflammatory activities. These properties make them desirable to be utilized in a wide range of therapeutics. Despite their importance, several challenges make their extractability and identification complex, for example, the unavailability of standards and their presence at low concentrations in seaweed matrices. This study reviews the analytical techniques utilized for the characterization of phlorotannins, highlights the associated challenges, and suggests potential solutions to overcome these challenges and improve the precision and reliability of phlorotannin analysis in future studies. Despite the longstanding use of conventional solid-liquid extraction (SLE) for the extraction of phlorotannin, recent studies have shifted toward more environmentally sustainable techniques. This study also highlights the critical importance of selective multi-step purification in improving the measured total phlorotannin content (TPC) and the number of identified phlorotannins by effectively removing interfering matrices, such as lipids and proteins. Nuclear magnetic resonance (NMR) and mass spectrometry (MS) have proven successful in the tentative identification of phlorotannins. However, achieving the highest level of identification confidence remains challenging due to the unavailability of standards. For quantification, the 2,4-dimethoxybenzaldehyde (DMBA) assay and quantitative NMR technique offer greater precision and specificity for phlorotannins, whereas the Folin–Ciocalteu (FC) assay tends to overestimate phlorotannin content due to quantifying other phenolic compounds.