Effect of lecithins on BCG-alginate-PLL microcapsule particle size and stability upon storage

Alginate-PLL microcapsules containing BCG were prepared by emulsification/internal gelation of an alginate solution dispersed within a vegetable oil containing lecithins as emulsifiers. The lecithins studied were soy bean lecithin at 0.1, 0.5, 1 and 2% concentration; and dried egg yolk lecithin at 0.1, 0.25, 0.5 and 1%. The microcapsule particle size showed a dependence upon the amount and type of lecithin added to the oil. Increasing the emulsifying agent concentration was found to reduce particle size, from 50.9 microm obtained when lecithins were not used in the emulsification step, to 13.9 microm obtained when 1% dried egg yolk lecithin was employed. The encapsulated BCG was identified by the Difco TB stain set K, followed by observation under optical microscopy. Once prepared, microcapsules were freeze-dried using 5% trehalose as cryoprotectant in order to preserve their stability upon storage. The stability of the microcapsules was assayed over 12 months at room temperature, finding that alginate-PLL microcapsules were stable up to 6 months. Moreover, in the case of microcapsules prepared with lecithins, a significant increase in particle size was observed, from 16.9 microm at the beginning of the study to 25.2 microm at 12 months storage.