Production and structural characterization of a new type of polysaccharide from nitrogen-limited Arthrospira platensis cultivated in outdoor industrial-scale open raceway ponds

Abstract

Background: Carbohydrates are major biomass source in fuel-targeted biorefinery. Arthrospira platensis is the largest commercialized microalgae with good environmental tolerance and high biomass production. However, the traditional target of A. platensis cultivation is the protein, which is the downstream product of carbohydrates. Aiming to provide the alternative non-food carbohydrates source, the feasible manipulation technology on the cultivation is needed, as well as new separation methodology to achieve maximum utilization of overall biomass. Results: The present study aimed to demonstrate the feasibility of industrially producing carbohydrate-enriched A. platensis and characterize the structure of the polysaccharide involved. Cultivated in industrial-scale outdoor open raceway ponds under nitrogen limitation, A. platensis accumulated maximally 64.3%DW of carbohydrate. The maximum biomass and carbohydrate productivity reached 27.5 g m-2 day-1 and 26.2 g m-2 day-1, respectively. The efficient extraction and purification of the polysaccharides include a high-pressure homogenization-assisted hot water extraction followed by flocculation with a non-toxic flocculant ZTC1 + 1, with the polysaccharide purity and total recovery reaching 81% and 75%, respectively. The purified polysaccharide was mainly composed of (1→3)(1→4)- or (1→3)(1→2)-α-glucan with a molecular weight of 300-700 kDa, which differed from the commonly acknowledged glycogen. Conclusions: By the way of controlled nitrogen limitation, the high carbohydrate production of A. platensis in the industrial scale was achieved. The α-glucan from A. platensis could be a potential glucose source for industrial applications. A non-toxic separation method of carbohydrate was applied to maintain the possibility of utilization of residue in high-value field.