This study utilized phosphorus starvation stress to regulate the efficient carbon fixation and functional glucan production in Arthrospira platensis.The structure of glucan obtained at different culture times (the 6th and 8th day) was characterized by infrared spectrum, monosaccharide composition analysis, 1H nuclear magnetic resonance, gel permeation chromatography, and dynamic light scattering, and its dietary fiber content, digestive characteristics, and in vitro immune activity were evaluated.Compared to normal P (+P) conditions, phosphorus starvation (-P) stress increased the CO2 fixation efficiency of Arthrospira platensis by 36.8%, reaching 0.53 g CO2/(L·d), and the α-glucan content and yield increased to 38.9% and 0.99 g/L, respectively.The glucan obtained on the 6th day of -P (G6) was mainly composed of 89.38% glucose, which was an α-1→4 glucan with α-1→6 branches.The branching degree of G6 was 5.82%.G6 contained three glucan components with different molecular weights:high molecular weight (HMW), medium molecular weight (MMW), and low molecular weight (LMW), with the average molecular weight of 9 461.7, 4 152.5, and 2 388.2 kDa, respectively.The corresponding molecular chain conformations were rigid rod-shaped, spherical, and highly branched structures.G8 had similar structures and compositions with G6, but the branching degree was higher, the molecular size was larger, and the HMW component had a tighter structure than G6, while the structure of MMW and LMW was looser.G6 and G8 had lower rapid digestible components than maltodextrin (MD), and the dietary fiber contents were 26 and 12 times higher than MD, respectively.Both G6 and G8 could induce the secretion of NO, TNF-α and IL-6 in macrophages RAW264.7, and G6 had a better immunomodulatory activity than G8.-P can serve as a regulatory strategy for efficient carbon fixation in Arthrospira, and the regulation products α-glucans have the potential to be developed as slow digestive functional foods containing prebiotics with immunomodulatory activity.
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