Bioactive polysaccharides and their derivatives from microalgae: biosynthesis, applications, and challenges

Microalgae are a major primary producer in the ocean, contributing up to 50% of global primary production. Bioactive compounds from microalgae include carotenoids, such as beta-carotene, lutein, and essential fatty acids, such as docosahexaenoic acid and eicosapentaenoic acid, have been attractive as natural products for decades. Recently, polysaccharides and their derivatives from marine microalgae have drawn much attention as the biodiversity of microalgae offers great opportunities for discovering novel bioactive compounds. Marine microalgae, including diatoms, are rich sources of sulfated polysaccharides, which have shown antiviral, antioxidant, antiinflammatory, antiparasitic, and antitumor activities. Although the mechanisms underlying the biological activities of microalgal polysaccharides are not fully understood, their positive effects on the human body are mostly associated with their prebiotic activity. In this review, a variety of microalgae with different types of polysaccharides and oligosaccharides are described. For the screening of bioactive compounds, extraction and purification methods are also introduced to explore the composition and efficacy of polysaccharides in microalgae. Biosynthetic pathways of polysaccharides are summarized, and their biotechnology applications are illustrated accordingly. This chapter demonstrates the biological activities of polysaccharides and their derivatives from microalgae and potential use in human health and other industrial applications. The current challenges in the microalgal polysaccharide field are highlighted. Finally, conclusions and future scope are also provided.