Developing coating strategies for microaerogel beads to modulate bioactive release in foods

Abstract

The potential of aerogels, highly porous materials with an extensive surface area, to be used as ingredients able to load, protect and deliver bioactive compounds in food has recently attracted significant attention. However, the open-porosity of aerogels favours rapid absorption of both water and digestive fluids, triggering structural collapse and uncontrolled release of the loaded bioactives. In this study, a hydrophobic coating layer was used to finely modulate bioactive release from aerogels. To this aim, aerogel beads were prepared by gelling whey proteins at the isoelectric pH, followed by solvent exchange and supercritical-CO₂ drying. The resulting beads showed the typical whey protein microaerogel structure, with interconnected globular particles and a defined mesoporous network, providing a specific surface area of 27 m²/g estimated by QSDFT analysis, which was suitable for bioactive loading. The microaerogel beads were loaded with vanillin, selected as a representative bioactive molecule, and dip-coated in an ethylcellulose (EC) ethanolic solution at varying concentrations (1, 5, and 10 g/100 g). Coating application resulted in the formation of a protective coating layer, with thickness increasing with the EC concentration in the dipping solution, and this led to a marked reduction in the accessibility of microaerogel mesoporosity to N₂ sorption. Uncoated beads exhibited rapid Fickian diffusion of vanillin, while coating application shifted the transport mechanism toward a slower, barrier-controlled mass transfer. These results support aerogels as innovative food-grade delivery systems for controlled release of compounds with target functionalities in foods.