Phlorotannins as Bioactive Agents from Brown Algae: Chemical Characterization and Extraction Methods ^†

Marine organisms, especially brown seaweeds, have attracted a lot of attention worldwide because of their potential for use in treating a range of infectious and non-infectious diseases, being able to take part in the creation of medications and nutraceuticals intended for ingestion by humans. Brown algae are a source of compounds, including phlorotannins (PTs), that exhibit biological effects, like anti-inflammatory, antibacterial, antioxidant, anti-tumor, anti-diabetic, and UV radiation protection [1,2]. As a polyphenol (tannin), this compound has the intrinsic capacity to scavenge and reduce free radicals. It can also present a high affinity for proteins through specific or non-specific interactions, interact with multiple receptors, control enzyme activity, cross-link biological macromolecules, inactivate microorganisms, and regulate signal transduction. These properties suggest that PTs may find widespread use in tissue engineering. Furthermore, according to related studies, at most dosages, PTs from brown seaweeds have shown minimal toxicity in invertebrates, animals (mice, rats, fish, and dogs), and humans [3]. PT algae have been commonly characterized using assays like Folin–Ciocalteu and 2,4-dimethoxybenzaldehyde (DMBA). However, due to their complex mixtures, identifying them accurately is challenging. Techniques like MS/MS coupled with HPLC aid in tentative characterization, but some authors advocate for NMR for precise identification, linking structures to HPLC conditions for a comprehensive analysis [4]. Solid liquid extraction (SLE) with hydroacetonic blends has remained the preferred method for extracting PTs and tannins in general, despite its limitations in sustainability and environmental impact. Factors like solvent polarity, pH, temperature, time, and pre-treatments are said to influence the effectiveness of solvent-based extraction procedures. However, emerging methods such as microwave-assisted extraction (MAE), pressurized liquid extraction (PLE), ultrasonic-assisted extraction (UAE), and supercritical fluid extraction (SFE) offer more eco-friendly alternatives to address these drawbacks, enhancing extraction efficiency. This communication conducts a literature review about PTs, their chemical characterization, and the most appropriate extraction methods [2,5].