Subtilisin absorptive encapsulation and granulation

Subtilisin granules were formulated by absorptive encapsulation, whereby preformed absorbent alginate microspheres or granules are loaded in enzyme concentrate. Subtilisin payload and activity yield of the granules were as high as 764 mg protein/g granules and 93%, respectively. The diffusivity of subtilisin into alginate gel beads ranged from (1.47 to 6.69) × 10−5 cm2/min, and increased as alginate concentration decreased, alginate G-content decreased, or polyvinyl alcohol (PVA) loading increased. Rapid protein absorption by granules was mainly due to rehydration in the enzyme concentrate with close to 90% protein loading in 5 min, leading to an equilibrium payload of 571 mg protein/g granules. Since over 50% dry weight consisted of subtilisin, this represents a payload considerably higher than that achieved by most other granulation technologies. Enzyme granules containing 30% PVA disintegrate rapidly in detergent solution, releasing over 50% of the protein within 3 min, a desirable feature for detergent application. With PVA and potentially other excipients, the controlled release property of the granules can be modified. The novel absorptive encapsulation approach is proposed as a promising technology platform for the encapsulation of subtilisin and potentially for other biological activities.