CHANGING THE PH OF THE EXTERNAL AQUEOUS-PHASE MAY MODULATE PROTEIN ENTRAPMENT AND DELIVERY FROM POLY(LACTIDE-CO-GLYCOLIDE) MICROSPHERES PREPARED BY A W O/W SOLVENT EVAPORATION METHOD/

The milk model protein, beta lactoglobulin (BLG), was encapsulated int o microspheres prepared by a multiple emulsion/solvent evaporation met hod. The effect of the pH of the outer aqueous phase on protein encaps ulation and release as well as on microsphere morphology has been inve stigated. At all tested pH values, the encapsulation efficiency was sh own to decrease with increasing the initial amout of BLG. This was cor related with the reduced stability of the primary emulsion as the init ial BLG increased. In addition, reducing the solubility of BLG in the external aqueous phase by decreasing the pH to the isoelectric point o f BLG (pI 5.2) resulted in an improved protein encapsulation. Moreover , it was shown that combining pH modification and optimal stability of the first emulsion yielded microspheres with a high encapsulation eff iciency. However, release kinetic studies revealed that a significant burst release was observed with microspheres loaded with large amounts of BLG, especially when prepared in a medium at pH 5.2. This burst ef fect was attributed to morphology changes in the microsphere surface w hich was characterized by the presence of pores or channels able to ac celerate the release of BLG. These pores were assumed to result from t he presence of large amounts of protein molecules on the microsphere s urface, that aggregate during microsphere formation at pH 5.2. Indeed, single adsorption experiments have shown that BLG had a higher affini ty for the particle surface when the pH was close to the pi. Thus, red ucing the solubility of a protein in the external aqueous phase allows the product of microspheres with a better encapsulation efficiency, a lthough this benefit is provided by a strong adsorption of the protein on microsphere surface.