Characterization and Function of a Novel Extracellular Polysaccharide from a Green Alga Parachlorella sp. AMI5

The green alga Parachlorella sp. AMI5 is a newly identified strain that produces a substantial amount of the unique extracellular polysaccharide amiEPS. This study aimed to investigate the purification, characteristics, and function of amiEPS-N from the AMI5 strain cultivated in a nitrogen-deficient BG11 (BG11-N) culture. We successfully obtained a high yield of 1.08 g/L of purified amiEPS-N with low protein content. Characteristic analyses revealed that amiEPS-N was composed of a flexible molecular form with 0.51 ± 0.00 log (nm)/log (g/mol) of a conformation plot slope in the water solution, and the weight average molecular mass was 1.73 × 10⁶ g/mol in maximum. The monosaccharide composition of amiEPS-N was rhamnose:xylose:glucuronic acid as 55.1:34.8:10.1 (mol%), indicating that it is an acidic rhamnan. The aqueous amiEPS-N exhibited anti-angiotensin-converting enzyme and tyrosinase-enhancing activities, which may contribute to the anti-hypertensive effects and inhibition of gray hair, indicating its novel and unique properties. The biochemical characteristics of the novel amiEPS and the contribution of this production technology to the social implementation for biorefineries are discussed.