ABSTRACT
Algae have been a major component in the daily diet in many of the Asian countries since ancient times, and among diverse biomolecules algal carbohydrates are important for their unique nutritional and health effect. Algae use diverse types of polysaccharides for energy storage and structural purposes. Among these polysaccharides, many are digestible by humans as they are evolutionarily equipped with various amylases and produce mono- and disaccharides, which are assimilated in energy production or serve other different functional purposes. Other complex carbohydrates comprise a group that are resistant to human digestive enzymes and are called “human inert” polysaccharides or “dietary fibre.” These dietary fibres do not directly take part in energy metabolism. However, these indigestible polysaccharide fibres have many beneficial extra-nutritional physiological effects in humans. For example, “soluble fibres” are the essential components of all the algal polysaccharides amounting to >50% and >70% of total dietary fibres in green and brown microalgae; these get partially fermented in the large intestine to variable degrees depending on the enzymatic competence of the microbiome. The fermentation products of these “soluble fibres” are short chain fatty acids like propionates, butyrates, etc., which take part in nourishing the epithelia of the large intestine and offer other benefits to the host, like regulation of signalling associated with energy homeostasis and immune reactivity. Among other functionalized polysaccharides of algal origin alginates, sulphated glycans, laminarans, fucoidans, etc. are of utmost importance for their exclusive food and nutraceutical effects. The chapter will encompass the structural aspects, chemical processing, nutritional and nutraceutical significance of algal polysaccharides.
