Production of BCG alginate-PLL microcapsules by emulsification internal gelation

A biocompatible emulsification method for microencapsulation of live cells and enzymes within a calcium alginate matrix applied to Bacillus Calmetre-Guerin (BCG) has been developed. Small-diameter alginate beads (microcapsules) were formed via internal gelation of an alginate solution emulsified within vegetable oil. Five different oils (sesame, sweet almond, perhydrosqualene, camomile and jojoba) were used. The rheological analysis of the oils showed a Newtonian behaviour, with viscosities=30.0, 37.7, 51.2, 59.3 and 67.1 mPa.s for perhydrosqualene, jojoba, camomile, sesame and sweet almond oil respectively. The particle size of the microcapsules obtained ranged from 30.3 mu m for the microcapsules prepared with sweet almond oil to 57.0 mu m for those made with perhydrosqualene. The mean particle diameter obtained was found to be dependent on the viscosity of the oil employed, according to the equation: empty set (mu m) = 76.6-0.628 eta (mPa.s) (r(2) = 0.943). The encapsulated BCG was identified by the Difco TB stain set K, followed by observation under optical microscopy. Freeze-drying of the microcapsules was carried out to ensure their stability during storage. Two batches of microcapsules (those prepared with sesame and jojoba oil) and four types of cryoprotectors (glucose, trehalose, mannitol and sorbitol), at three concentration levels (5, 10 and 20% w/v) were studied. The parameters evaluated were particle size, physical appearance, reconstitution of lyophilizates and microscopical evaluation. For both batches of microcapsules the best results were obtained with trehalose 5%, showing particle sizes of 42.1 mu m in the case of the microcapsules prepared with sesame oil, and of 45.3 mu m for those prepared with jojoba.