Institute of Fundamental Technological Research

Hydrophobic food ingredients sensitive to degradation can be protected from their environment by microencapsulation. In an O/W1/W2 system, these hydrophobic compounds are dissolved in oil droplets, dispersed within a gelled matrix microbead (W1), which forms a barrier. The stability and degree of protection delivered by the gel matrix depends on its structure and strength, which in turn depend on the gelling process. For heat sensitive ingredients this process is typically a cold-set gelling process.

We investigated the effect of variations in matrix polymer (alginate and WPI aggregates), gelling agent (acid and calcium), and method of gelation (internal and external), on the ability of microbeads to retain oil droplets, and retain a spherical shape during the extraction from the oil phase.

External gelation with CaCl2 nanoparticles gave the smoothest and strongest microbeads for both protein and alginate, which we attribute to the formation of a shell at the interface of the bead during gelation. Microbeads produced by internal calcium gelation (induced with CaCO3 nanoparticles and GDL) containing the same amount of calcium showed less integrity and gave a mixture of smooth and rough beads. About half of the microbeads produced by acid induced gelation of WPI aggregates (using GDL to lower the internal pH) remained intact. When the pH was brought further from the isoelectric point, fewer beads remained intact. The method of gelation proved to be more important for the microbead integrity than type of matrix polymer, and external gelling was clearly superior to internal and acid induced gelation.

Cold-set gelation, Microbeads, Encapsulation, Strength, Gelation methods

Oil-soluble components can be encapsulated in an O/W1/W2 microsystem, in which they are dissolved in oil droplets dispersed in a gelled microbead (W1), which forms a barrier between the oil droplets and the aqueous continuous phase (W2). We investigated the rate and mechanism of breakdown of protein microbeads in a simulated gastric system, and studied the influence of microbead protein concentration, gelling method (cold-set, slow and fast heat-set), and further processing (freeze-drying), on the breakdown process. Breakdown rate decreased with increasing protein content of the beads, for the same method of production. Due to the porosity of the slowly-heated heat-set beads, breakdown occurred evenly throughout the entire bead. Cold-set microbeads of 10% protein broke down slightly slower than the heat-set microbeads of 15%. The denser surface of the 10% beads slowed down the diffusion of the enzymes into the bead's interior, causing the beads to be broken down from the outside inward. All these beads broke down within one hour. Increasing the rate of temperature increase during the heating step dramatically slowed breakdown. There was no significant breakdown of rapidly heated beads within 138 minutes, even though no difference in microstructure between rapidly and slowly heated beads was visible with electron microscopy. Freeze-drying of the beads also slowed their breakdown. After 132 minutes more than half the measured particle volume of were intact beads. Freeze-drying changed the microstructure of the beads irreversibly: rehydrating the dried beads did not result in a breakdown behaviour similar to that of unprocessed beads.