Extraction of bioactive compounds from beach-cast brown algae: a review on accelerated solvent extraction and subcritical water extraction

Brown algae accumulation on beaches, or beach-cast, can lead to negative environmental impacts. However, beach-cast brown algae harvested from coastlines is a potential resource of bioactive compounds for use in food, biomaterial, cosmetic, and pharmaceutical industries. The extraction and subsequent separation and purification of bioactive compounds using conventional Solid-Liquid Extraction (SLE) requires improvement for sustainability and efficiency. Subcritical water processes are a potential "greener" approach in extraction without a decrease in process performance. This review outlines the bioactive compounds (alginate, fucoidan, laminarin, phenolic compounds, and fucoxanthin) in beach-cast brown algae and summarizes and compares conventional SLE and pressurized water methods: Accelerated Solvent Extraction (ASE) and Subcritical Water Extraction (SCWE). ASE is typically used in characterization/analysis, while SCWE is more appropriate for production. Extraction rate models and challenges related to scale-up in ASE and SCWE are also reviewed. ASE and SCWE can selectively extract bioactive compounds by modifying temperature/pressure and solvent combinations, and minimize extraction time, maximize yields and rates, and reduce chemical/solvent usage compared to SLE. However, kinetic modeling and scaling up of pressurized systems for brown algae valorization is still in its infancy. Future research is required to determine the green solvent combinations, develop batches into continuous processes, balance extraction conditions with product quantity and purity, and scale up for industrial-scale production. Pressurized water extraction techniques (ASE and SCWE) are potentially more sustainable for extracting bioactive compounds from beach-cast brown algae than conventional solvent extraction on both small and large scales.