A review on integrated biorefining of brown algae focusing on bioactive compounds and holistic biomass valorisation

Brown algae (BA) represent a great source of sustainable bioproducts such as bioactive substances with beneficial health properties and biopolymers with industrial applications. Increasing demand for these bioproducts necessitates a holistic BA utilisation approach, requiring integrated biorefinery concepts that combine biomass pre-treatment, fractionation and downstream separation and purification technologies. This review discusses holistic BA valorisation focusing on bioactive secondary metabolites and their incorporation as products of BA biorefineries. It explores their structural diversity, identification and characterisation methods, and sustainable processing technologies. Polar phlorotannins, non-polar carotenoids, and sterols predominate bioactive compounds in BA. Phlorotannins in BA are structurally diverse and complex due to the presence of structural isomers. A cascade biorefinery concept can be developed using green technologies, potentially enabling the sequential recovery of up to six high-purity products. Lipophilic and phlorotannin enriched fractions are separately recovered using polarity-based fractionation assisted by cell wall disruption techniques, and separation and purification follow to recover proteins, fucoidan, alginate and algal cellulose-enriched fractions. Encapsulation is necessary to turn BA bioactive compounds into ready-to-use ingredients in functional food and nutraceutical industries.