Vitamin D-Loaded Microcapsule-Cod Protein Composite Gels: Texture, oral processing, and digestive properties

This study developed a functional gel system based on cod protein, incorporated with vitamin D-loaded bilayer microcapsules, to achieve both texture softening and nutritional enhancement through controlled moisture regulation and composite ingredients. Results demonstrated that the incorporation of microcapsules (5%-30%) significantly reduced cooking loss, gel strength, hardness, and gumminess, while improving whiteness ( p <0.05). Composite gels with 5%-15% microcapsules met the Level 6 (soft & bite-sized) criteria according to the International Dysphagia Diet Standardisation Initiative (IDDSI) testing, indicating their suitability for individuals with dysphagia. Particularly, the microcapsule content of 15% was identified as optimal. Microscopic observations confirmed that the microcapsules remained intact and demonstrated improved protein cross-linking, attributable to the addition of microcapsules enhancing hydrophobic interactions. However, excessive incorporation (30%) disrupted the three-dimensional network architecture of the gel. In vitro digestion results indicated that the soft gels with 15% microcapsules achieved a high protein digestibility of 91.83% and enhanced vitamin D bioaccessibility, compared to the free-form vitamin D with release rate of 57.46%. Furthermore, the composite gels with 15% microcapsules exhibited improved oral processing properties, including lower friction coefficient and reduced masticatory force, fulfilling both swallowing safety and nutritional requirements for populations with special dietary needs.