The effect of core oil on the encapsulation efficiency and mechanical properties of microcapsules prepared using complex coacervation followed by spray drying/coating

Gelatine-gum Arabic coacervated microcapsules were prepared using complex coacervation followed by spray drying, with L-carvone, limonene, or hexyl salicylate encapsulated as a model flavour or fragrance oil. The influences of different types of core oil or further treatments including maltodextrin coating or glutaraldehyde crosslinking on size, morphology, payload, encapsulation efficiency and mechanical strength of the resulting microcapsules were investigated. Spherical microcapsules with polynuclear core-shell structure were fabricated. The encapsulation efficiency ranged from 5.0 +/- 0.4% to 89.0 +/- 1.2% for different core oils and 21.1 +/- 0.1% to 89.0 +/- 1.2% after different treatments. The highest encapsulation efficiency of 89.0% +/- 1.2% was obtained for encapsulating hexyl salicylate with a hardening process by glutaraldehyde crosslinking. Micromanipulation tests revealed that gelatine-gum Arabic microcapsules exhibited typical rupture behaviours under compression. The rupture force increased with microcapsule diameter, the nominal rupture stress and toughness decreased with the increase of microcapsule size, and the nominal rupture tension was independent of diameter. The apparent Young's modulus of whole microcapsules was determined by the Hertz model fitted to the experimental force versus displacement data. It has been found that different types of core oils significantly impacted their encapsulation efficiency, the structures of the formed microcapsules, and consequently mechanical properties.