β-Glucuronidase activity following complex coacervation and spray drying microencapsulation

Abstract

The objective was to develop a microencapsulation process suitable for the controlled release of an active protein drug. β-glucuronidase was selected as a model protein and a combination of complex coacervation (gelatin/sodium alginate, gelatin/acacia and albumin/acacia) and spray drying was investigated. Coacervates were either spray dried or glutaraldehyde crosslinked to form microcapsules. Polyvinylpyrrolidone (PVP) and polyethylene glycol were investigated as potential coacervate enhancers and stabilizers. β-glucuroni-dase/polymer mixtures were spray dried to determine any polymer protective effects on protein activity. A BÜCHI 190 Spray Drier was used, β-glucur-onidase activity was determined using a Sigma Kit and microcapsule particle size was measured by Accusizer analysis (light blockage). All non-crosslinked coacervates investigated, with the exceptions of albumin/acacia and albumin/ acacia/β-glucuronidase/PVP, were unsuitable for spray drying as they rapidly phase separated and blocked the spray drier nozzle. β-glucuronidase activity in the albumin/acacia coacervates approximated to 99% prior to and 80% following spray drying. This can be compared to activities of approximately 30% and 68% when spray dried alone and with albumin, respectively, and of 18% in albumin/ acacia microcapsules crosslinked with glutaraldehyde. Microcapsule particle size was affected by coacervation pH, additives and spray drying. In vitro β-glucuronidase release was biphasic, with an initial burst release followed by a zero order release phase and continued over the 12 day study period. In conclusion, the spray drying albumin/acacia/PVP method described is useful for the preparation and collection of controlled release microcapsules with minimal loss of β-glucuronidase activity.