Characteristics and function of an extracellular polysaccharide from a green alga Parachlorella

The green alga Parachlorella sp. BX1.5 is a new strain that can significantly coproduce lipids and polysaccharides, inside and outside the cells, respectively. This study aimed to investigate the characteristics and functional properties of the extracellular polysaccharide (EPS). Ethanol-extracted EPS from the cells grown in N-starved BG11 medium was found to be a novel acidic rhamnan of straight-chain type, with a high molecular mass of > 1.75 × 10⁶ daltons. The water-soluble EPS exhibited high viscosity as sol, even at low concentrations, with 0.5 % EPS showing almost constant viscosity at 10-40 °C. Its addition to mayonnaise resulted in improved oil-off, suggesting its possible application as a thickener or food additive. Cells with added EPS were found to exhibit resistance to environmental stress conditions, such as heat, dryness, and decompression, and ultraviolet rays. Based on these rheological and biological effects, its unique properties with respect to biorefinery have been discussed here.