Compression behavior of the enzyme ß-galactosidase

This thesis is based on the investigation of the compression behavior of a solid model enzyme. It
was the scope of this work to characterize the behavior of the enzyme powder under pressure to
gain on the one hand information about the behavior of powder during the compression process
and on the other hand to get more knowledge about the behavior of enzyme powder in
pharmaceutical formulations. An important aspect was the influence of excipients because their
deformation character may change the properties of pharmaceutical formulations. For that reason
the physical influences of a plastic and a brittle model excipient, respectively on the enzyme
powder in binary mixtures was investigated. Critical mixture ratios should be defined where the
behavior of the binary mixtures shows sudden changes. If critical mixture ratios are known, they
can be avoided in the development of dosage forms to get robust formulations. Since the direct
compaction of powders may be difficult, the compression behavior of enzyme granulates and
enzyme coated pellets was investigated as well. For that reason powders and pellets from different
raw materials were layered with an enzyme binding agent solution. The enzyme activity of the
various granulates, pellets and compacts was detected and the preparations were judged based on
this property. The investigated model enzyme was a solid β-galactosidase preparation from Aspergillus oryzae,
which was chosen for its stability, the molecular weight of 105 kDa, which is an average value
compared to other enzymes and the reliable and relatively simple enzyme activity assay.
Compacts were produced on a material testing machine and the activity was detected
spectophotometrically. The compression properties of the various formulations were characterized
by using Heckel equation and modified Heckel equation. Granulates and pellets as well as their
compacts were further characterized by scanning electron microscopy pictures. The extent of activity loss in the compacted brittle enzyme powder could not be decreased by the
addition of a plastic or a brittle excipient. With the diversity of the particles even a higher number of
shearing forces was built in the compacts during compression. The shearing forces seemed to
have negative influences on the activity of the enzyme. In the binary powder mixtures of the
enzyme powder with the plastic excipient there was found a sudden change in the behavior of the
system at a mixture ratio of 20% of enzyme powder. For the brittle-brittle binary mixtures of the
enzyme powder with an excipient, differences in the behavior were difficult to detect because the
two powders showed a very similar behavior. Tendencies towards a critical concentration at a ratio
of 60% (V/V) of enzyme powder could not be proved, although a comparison with a second brittle
enzyme powder preparation in mixtures with a brittle excipient showed similar tendencies. It was
found that a plastic compression character and regularity in shape and size of the compressed
particles was important to protect the enzyme activity under pressure. These properties could be
reached with the production of granulates and the coating of pellets by enzyme layering, whereas especially the compacted enzyme coated pellets showed no significant activity loss under pressure
due to the very regular shape and size distribution and the fact that the pellets did not break and
only slightly changed their shape to reduce the spaces between the individual pellets.
A lot of new aspects in the field of particle compression have been discussed in this work. It was
found that the shape and the size of the various particles may have big influences on friction and
shearing forces. Shearing forces can cause a reduction of enzyme activity during the compression
of an enzyme powder. The compression character of the particles showed influences on the extent
of activity loss under pressure, whereas plastic properties are favorable to protect the enzyme.
As a further step it would be important to test the transferability of the results on other enzyme
products and to take into consideration more practical aspects like the production on a rotary press,
the investigation of economic points of view or simply the attainment of a required dosage to define
an optimal formulation for an oral application of a pharmaceutical enzyme powder.