ABSTRACT
I. Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 II. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 III. Dry Coating. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 IV. Different Approaches for Coating Particles Without Wetting . . . . . . . . . . . . . . . . . . . . . . 182
A. Use of Nonaqueous Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 B. Hot-Melt Coating. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 C. Dry Particle Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
1. Dry Impact Blending (Mechanochemical Treatment or Hybridization) . 185 2. Mechanofusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 3. High-Speed Elliptical-Rotor Type Mixer (HEM or Theta Composer) . . . 186 4. Rotating Fluidized Bed Coater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 5. Magnetically Assisted Impaction Coater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
D. Use of Plasticizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 V. Coating of Crystalline Cellulose Granules Using AQOAT — A Case Study . . . . . 188
A. Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 1. Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 2. Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 3. Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
VI. Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 A. Coating Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 B. Hydration During Coating Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 C. Permeability of the Shell (Hydration of Granules During Storage). . . . . . . . . . . 192 D. Dispersion of the Coating Shell in Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
VII. Conclusion and Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
ENPO: “dk2963_c007” — 2005/3/21 — 18:23 — page 180 — #2
I. SUMMARY
Dry coating is suitable for coating of core materials that must not be wetted during processing, for example, some pharmaceuticals and most of the neutraceuticals. Different dry coating processes are reviewed, particularly dry impact-blending, coating with plasticizer, and hot-melt coating. A specific case is presented in which spherical granules made of crystalline cellulose (750 to 800 mm) are coated by a fine powder (AQOAT) using triethyl citrate as plasticizer. The examined characteristics are the water barrier properties, their water content, and their quick solubility. The results show that the AQOAT film presents fast dissolution in water (2.5 min) and relative protection. Unfortunately this protection is not sufficient in certain cases, for example, the 2% moisture content of the resulting coated granules is not satisfactory for probiotics requirements, even if this value is smaller than the one obtained with the aqueous coating system. Finally, dry coating using a plasticizer appears quite adequate for coating moisture-sensitive food products but this requires some improvement of the processing conditions.
