Empty yeast cells are used as a new delivery system for flavor encapsulation. The flavor release mechanism from yeast cells is characterized using a series of analytical techniques, and limonene is used as a model representing a hydrophobic flavor. Furthermore, the thermal stability of the capsules was assessed. The characterization of the cell wall structure gives rise to the development of an empirical model explaining water adsorption as well as the desorption singularities observed on drying. The study of the rate of flavor release as a function of temperature and water uptake in the cell wall clearly demonstrated a particular behavior of the yeast cell wall permeability. Below a water activity around 0.7, no flavor release is permitted whereas release occurs above it. Surface analysis on dry or wet cells using atomic force microscopy is discussed.
Composite polyurea/coacervate core/shell capsules are formed by coupling associative biopolymer phase separation with interfacial polymerization. They combine the excellent chemical stability of synthetic polymer barriers with the strong adhesive properties of protein-based complex coacervates, inspired by biological underwater glues. To encapsulate volatile oil droplets, a primary coacervate hydrogel capsule is formed by a protein and weak polyanion and is reinforced with a polyurea membrane synthesized in situ at the interface between the coacervate and the oil core. The polyurea layer provides an excellent permeability barrier against diffusion of small volatile molecules while the coacervate portion of the shell enhances adhesion on the targeted substrate.
In case of emergency, break glass: Biohybrid core/shell capsules (see picture) suitable for encapsulation of volatile molecules can be formed through precipitation of amorphous silica in a protein/polyanion coacervate scaffold. The coacervate molds the final shape and structure of the capsule shell and provides an acidic microenvironment to locally induce hydrolysis and condensation of liquid silica precursors.
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