Colored, opaque sugar coating suspensions for application to solid matrix systems
Abstract
An opaque, colored sugar coating system and its components were investigated. The pH-dependent surface charge of food grade titanium dioxide of the anatase crystalline form, present as an opacifier in the sugar coating system, was studied. From potentiometric titration studies, the PZC of the titanium dioxide was observed to be much lower than that normally reported for titanium dioxide. Treatment of the titanium dioxide to remove impurities was found to increase the PZC affecting the surface charge. The adsorption of FD&C yellow #5 and methylene blue by the titanium dioxide and the relative stability of aqueous dispersions of the titanium dioxide were found to be dependent on the surface charge as determined by the pH-PZC relationship. Dye adsorption was also dependent on the particle size of the titanium dioxide. The color stability with respect to pH of aqueous solutions of four FD&C dyes which are commonly used in sugar coating was also studied. Three of the dyes; FD&C red #3, FD&C yellow #5, and FD&C yellow #6 were found to undergo pH-dependent color changes which may be related to the chemical structure of the dyes. In addition, the apparent pKa values of FD&C yellow #5 and FD&C yellow #6 were determined spectrophotometrically. A number of compounds were evaluated for their ability to replace titanium dioxide as the opacifier in the sugar coating system. The color of the coatings produced with these compounds was a primary concern and was evaluated using reflectance spectroscopy and tristimulus colorimetry. Based upon color, all of the compounds studied were deemed unacceptable for use in the sugar coating system. The fracture resistance of titanium dioxide containing sugar coatings when subjected to a mechanical stress was studied using a stress analyzer. The fracture resistance of the coatings was found to vary with storage time and the level of titanium dioxide present in the coating. The utility of the stress analyzer in evaluating the fracture resistance of thin sugar coatings was demonstrated.
Degree
Ph.D.
Advisors
Peck, Purdue University.
Subject Area
Pharmaceuticals
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