Ultrasonic emulsification of alginate nanogel formulation for phycocyanin encapsulation

• A novel emulsification-gelation route produces alginate nanogels for PC delivery. • Internal gelation surpasses external gelation in PC encapsulation performance. • Internal gelation yields stable PC-loaded nanogels with high encapsulation (>80%). • Alginate nanogels provide strong PC protection under SGF conditions (pH 1.2) • Nanogels resist PC loss in SGF and enable sustained release in SIF. Encapsulation strategies are essential for stabilizing sensitive bioactive compounds and enabling their practical application in food systems. Phycocyanin (PC), a natural pigment-protein with antioxidant and functional benefits, is highly unstable under acidic pH, elevated temperature, and light exposure, limiting its industrial utilization. In this study, an ultrasonic emulsification approach was developed to fabricate alginate nanogels for PC encapsulation, systematically comparing external and internal gelation mechanisms. A stable water-in-oil (W/O) emulsion (15:85) stabilized with 2% (w/v) polyglycerol polyricinoleate (PGPR) was used as a template for nanogel formation. External gelation using 4% (w/v) CaCl₂ produced nanogels (∼250 nm) with limited encapsulation efficiency (<40%). In contrast, internal gelation mediated by 0.2 M Ca-EDTA generated nanogels of comparable size but significantly enhanced encapsulation efficiency (∼86%), demonstrating a more effective ion-release mechanism for uniform network formation. The optimized nanogels exhibited strong resistance to PC release under simulated gastric conditions (pH 1.2), while enabling controlled and sustained release in simulated intestinal fluid (pH 7.4). This dual functionality highlights their capability to protect PC during processing and digestion while improving its bioaccessibility. The proposed system offers an efficient platform for stabilizing natural pigments, with clear potential for applications in functional foods and nutraceutical delivery. These findings establish internal gelation-assisted alginate nanogels as a superior strategy for enhancing the stability and delivery performance of protein-based bioactive compounds.