Strain-dependent lactic acid bacteria fermentation modulates nutritional quality and bioactive properties of phycocyanin-rich extract from A. platensis

• Phycocyanin-rich extract from A. platensis was successfully fermented by LAB • Fermentation reduced phycobiliprotein levels and altered the free amino acid content • Biogenic amine levels were below any threshold values • L. plantarum -fermented samples displayed antibacterial activity Phycocyanin-rich extracts from Arthrospira platensis (spirulina) are hailed for their bioactive properties, amino acid composition, and micronutrient content. However, their further valorisation through microbial fermentation remains largely underexplored. In this study, we applied strain-dependent lactic acid bacteria (LAB) fermentation as a process-engineering strategy to modulate the biochemical profile and functional potential of phycocyanin-rich extracts under controlled anaerobic conditions. Lactiplantibacillus plantarum, Lactobacillus acidophilus , and Levilactobacillus brevis all achieved high cell densities within 24 h, accompanied by strong acidification linked to glucose utilisation and lactic acid formation. Fermentation induced characteristic strain-specific changes, including reductions in phycobiliproteins, shifts in free amino acid profiles, biosynthesis of water-soluble vitamins (notably thiamine and pyridoxine), and accumulation of biogenic amines at levels well below safety thresholds. Fermented extracts also exhibited antimicrobial activity, particularly in L. plantarum -fermented samples. These findings suggest that LAB fermentation can significantly alter the nutritional quality and biofunctional potential of phycocyanin-rich extracts, providing mechanistic insights and knowledge for the development of a next-generation fermented algal-based functional ingredients for future food systems.