Mixed-wall microcapsules made of cross-linked proteins and polysaccharides: preparation and properties

Microcapsules were prepared through an interfacial cross-linking process using terephthaloylchloride and applied to mixtures of a protein (human serum albumin or gelatin) and a polysaccharide. Their properties were compared with those of microcapsules prepared from the protein alone. Morphological characteristics of mixed-walled microcapsules were often modified, as seen by light and electron microscopy. Otherwise, they appeared to be more resistant to digestive media: they were gastroresistant, and their degradation time in pancreatin was prolonged upon raising the amount of polysaccharide. Moreover, the lysis time was shown to depend on the nature of the polysaccharide: microcapsules prepared from acidic polysaccharides at pH 9.8 were hydrolyzed faster. Lastly, the resistance increased upon decreasing the polymers/acylchloride ratio, or upon raising the reaction pH. Encapsulation assays were carried out with sodium salicylate, which was incorporated with a high efficiency. Mixed-walled microcapsules allowed a prolonged release of the tracer in vitro. As compared with protein microcapsules, the release profiles of batches prepared with hydroxyethylstarch exhibited only slight modifications of the initial part of the curve, while a significant burst effect was observed with carboxymethylcellulose-containing microcapsules.