An investigation of the properties of mixtures of starches with mono-myristic acid triglyceride as potential selectively digestible films

The aim of this work was the production of melt-films based on a mixture of unprocessed starch and a mono-myristic acid triglyceride for use as a coating on colon delivery formulations. The starches were embedded in the triglyceride-matrix during a melting process and drug release across the films was obtained by the digestion of the starch fraction through colonic α-amylases. During the first part of this study, the physicochemical properties of 7 starches, whose amylose content ranged from 0 % to nearly 100 %, were investigated and sub-sequently correlated by statistical analysis. The second part comprised the identification of the optimum film formula with respect to film-forming temperature, starch content and film thickness. A number of 4 and 7 starches were tested in a 3- and 2-factorial Central-Composite-Design experiment, respectively, and the effects and interactions of the film-forming parameters analysed by Analysis of Variance. The third part consisted of enzyme studies using 4 α-amylases of different origins as well as whole pancreatin in order to simulate and assess the selective film digestibility in the human intestinal tract. The film performance was measured as film permeability for the model drug phenylpropanolamine prior and after enzymatic digestion using a 2-chamber diffusion cell. The 3-factorial experiment revealed non-significance for the film-forming temperature, whilst the 2-factorial approach identified an optimum film thickness of 20 μm and a starch content of 30 %. These specifications were confirmed during the enzyme studies, where α-amylase from B.licheniformis produced the highest film permeabilities. The results showed that the degree of amylose content in the starch product is not as critical for film digestibility as the film thickness and starch content in the melt film. The particle size and surface area of the starches were found to be relevant for the digestibility and interpreted with respect to their accessibility for enzymatic attack