Compression behaviour of the enzyme beta-galactosidase and its mixture with microcrystalline cellulose.

The behaviour of beta-galactosidase powder under compaction was investigated to get more information on powder properties and to further characterise tablet excipients. The enzyme beta-galactosidase, the model excipient microcrystalline cellulose and several mixtures of these two substances were compressed at different compaction forces. The relative density of the obtained tablets was calculated and the Heckel equation as well as the modified Heckel equation was used to characterise the bulk powders and their mixtures. Microcrystalline cellulose is known as a model substance for plastic powders, the used beta-galactosidase was found to be a brittle substance. In further experiments, the activity loss of the compacted enzyme powder was investigated and used to characterise the behaviour of the binary mixtures in various ratios. Data interpretation with percolation theory led to a critical beta-galactosidase concentration of 20%. Between 100 and 20%, the enzyme builds a lattice and dominates the binary system. For beta-galactosidase amounts below 20% in mixtures with plastic excipients, the activity loss increases strongly because of higher shearing forces during compaction due to the system dominance of the plastic particles.