Phlorotannins, a seaweed based class of polyphenolic compounds, have proven to possess potential bioactivities such as antioxidant, antimicrobial, anti-allergic, anti-diabetic, anti-inflammatory, anti-cancerous, neuroprotection etc. These bioactivities have further increased demand globally and sustainable techniques such as supercritical fluid extraction, microwave assisted extraction, enzyme assisted extraction, extraction using deep eutectic solvents etc. are being explored currently for production of phlorotannin-rich extracts. In spite of such well documented bioactivities, very few phlorotannin-based nutraceuticals are available commercially which highlights the significance of generating consumer awareness about their physiological benefits. However, for industry level commercialization accurate quantification of phlorotannins with respect to the different classes is vital requiring sophisticated analytical techniques such as mass spectrometry, 1 H-NMR spectroscopy etc. owing to the wide structural diversity. This review summarizes the extraction and bioactivities of phlorotannins based on the findings of in vivo and in vitro studies.

Supercritical fluid extraction (SFE) has garnered significant attention as a promising green technology for the isolation of bioactive constituents from natural sources. In the present study, an attempt has been made to investigate the comparative effectiveness of supercritical carbon dioxide and conventional food grade solvents such as water, 60%, 40%, and absolute ethanol, in extracting bioactive compounds from brown seaweeds (Sargassum wightii and Turbinaria conoides). The antioxidant potential of seaweed extracts prepared using conventional methodologies and SFE was evaluated in terms of total phenolics, antioxidant activity, etc. SFE was significantly (p < .05) effective in extracting seaweed constituents with highest total phenolic (27.56 mg gallic acid equivalents/g extract), flavonoid, and total antioxidant activity compared to conventional solvents. Observations on biplots of principal component analysis also concurred with the above research findings. The present findings highlighted that SFE can be recommended as an environmentally friendly technology for obtaining antioxidant‐rich seaweed extracts with potential bioactivity. Practical applications Seaweeds, an important marine bioresource, serve as galore repository of biologically active phytochemicals such as fucoidan, phlorotannins, alginates, carotenoids, etc. Owing to their immense bioactivities, seaweeds/extracts and seaweed‐based biomolecules are finding extensive applications in the areas of pharmaceuticals, functional food, biotechnology, etc. Conventional extraction which is the most commonly employed method for obtaining seaweed extracts has so many drawbacks. In this context, the use of a sustainable method such as SFE garners significant attention. The present work highlights the potential of SFE in obtaining extracts with high bioactivity from commercially important seaweeds, S. wightii, and T. conoides.

Kappaphycus alverazii remains as a predominant source of kappa-carrageenan which is farmed extensively in Indonesia, Philippines and South East Asia. The current research focuses on the influence of concentration of salts and approach to dialysis on properties of carrageenan. Carrageenan due to its pronounced gelling and viscosifying properties, has gained significant usage in the areas of food, cosmetics, textiles, pharmaceutics, biomedicine, and numerous others. The process of extraction was conducted in a hot, alkaline condition at 80 oC for a duration of 2 hours. The alkaline substance used was KCl with 2% and 4% concentration and solvent to seaweed ratio was 20:1.Further, the resultant extracted samples were subjected to dialysis to evaluate the effect of dialysis on the quality of carrageenan. The absorbance peak at 849 cm–1 from Fourier Transform Infrared-Spectroscopy (FTIR) at all extraction conditions indicated D-galactose-4 sulphate related to kappa carrageenan obtained with no traces of \(\mu\)-precursor. The study demonstrated that the concentration of salts and the approach of dialysis have influenced the quality of yield, viscosity, gel strength, moisture content and ash content for the extracted carrageenan, which remains ideal for commercial applications.