The Effects of Rheological Properties of Wall Materials on Morphology and Particle Size Distribution of Microcapsule

The effects of rheological properties of the wall materials on the morphology and particle size distribution of microcapsules prepared by spray-drying were evaluated. Gelatin-sucrose (Gel-Suc), gelatin-peach-gum-sucrose (Gel-PG-Suc), and HI-CAP 100 were used as wall materials with vitamin A as a model core material. Scanning electron microscopy (SEM) showed that microcapsules produced with Gel-Suc exhibited cracks while Gel-PG-Suc produced a smooth surface with few pores, and HI-CAP100 a rounded surface containing characteristic concavities. The volume average diameter (D-4,D-3) showed significant variations from 73.9 +/- 1.02 mu m and 68.7 +/- 0.85 mu m to 29.9 +/- 0.94 mu m (P < 0.05). Rheometry indicated that the wall paste viscosity was inversely proportional to the shear rate. Viscosity ranking was Gel-Suc > Gel-PG-Suc > HI-CAP 100. Gel-Suc showed the highest elastic modulus (G') and viscous modulus (G '' values), followed by Gel-PG-Suc and HI-CAP 100. Gel-Suc was associated with moderate quantities of broken microcapsules while HI-CAP 100 generated numerous microcapsules with characteristic dents generated during spray-drying.