Fractionation and Functional Characterization of Limnospira platensis Extracellular Polysaccharides as Potential Food Ingredients from Recycled Cultivation Media

Limnospira platensis is a promising sustainable biomass for functional food production. During cultivation, it secretes extracellular polysaccharides (EPS) with underutilized potential as food ingredients. This study aimed to strategically fractionate Spirulina EPS (SEPS) by molecular weight (MW: <30, 30–100, >100 kDa) to elucidate their structure-function relationships for targeted food applications. We found distinct functional diversification: The mid-MW fraction (SEPS-2, 30–100 kDa) was an amphiphilic glycoprotein complex with potential interfacial activity. The high-MW fraction (SEPS-3, >100 kDa) formed a dense, glucose-rich glucan network, suggesting utility as a natural thickener or texturizer. In contrast, the low-MW fraction (SEPS-1, <30 kDa), rich in deoxy-sugars, exhibited superior antioxidant capacity, indicating potential as a bioactive preservative or nutraceutical. Spectroscopic and morphological analyses linked these structural differences to their physicochemical properties. Notably, the 30–100 kDa fraction transitions from a cultivation byproduct to a functional food architect, where its interfacial properties can be leveraged to engineer stable, clean-label emulsion-based food products. This work provides a foundation for the valorization of L. platensis EPS, demonstrating how MW-directed fractionation can unlock tailored functionalities-from bioactive agents to structural polymers-for the development of next-generation foods from circular bioeconomy streams.