Engineering robust bilayer water-in-water emulsions via protein–polysaccharide complexation: From interfacial stabilization to microencapsulation of sensitive bioactives

Water-in-water (W/W) emulsions are promising for delivering hydrophilic bioactives due to their biocompatibility and oil-free nature, but their application is hindered by poor stability. To address this, novel food-grade bilayer W/W emulsions were designed by employing amylopectin and tara gum as aqueous phases, stabilizing them with ovalbumin fibril (OVAF) or ovalbumin sphere (OVAS), and reinforcing them with a secondary carrageenan (CG) layer via electrostatic deposition. The results demonstrated that the bilayer emulsion OVAF/CG-stabilized TG/AMP emulsion (OFC-TE) was significantly more stable than OVAS/CG-stabilized TG/AMP emulsion (OSC-TE) across physical, thermal, freeze-thaw, and ionic stresses. It remained stable without phase separation for over 2 months. Subsequently, the delivery efficacy was validated by using riboflavin and Lactobacillus plantarum as model bioactives. The results demonstrated that OFC-TE provided significant protective effects. It not only retarded the photodegradation of riboflavin, limiting the fluorescence loss to only 27.81% after 8 h of UV irradiation, but also maintained Lactobacillus plantarum viability throughout pasteurization, freeze-thaw cycles, 28-day storage, and simulated gastrointestinal digestion. Furthermore, freeze-dried OFC-TE microcapsules displayed a honeycomb structure, enhanced thermal stability, and high Lactobacillus plantarum survival. This study provides an effective strategy for developing stable W/W emulsion delivery systems by engineering the interfacial structure, expanding their potential in functional foods for probiotics and vitamins.