Purpose. To crystallize lactose under static conditions with a view to prep
aring crystals of well-defined morphology.
Methods. alpha-lactase monohydrate was crystallized from neutralized Carbop
ol 934 gels. When the majority of crystals had grown to maturity, the gels
were acidified using diluted hydrochloric acid and the crystals were harves
ted by filtration or centrifugation and washed with ethanol-water mixtures.
Results. Crystals prepared from the gel had a consistently narrower size di
stribution than control crystals, prepared from solution under constant sti
rring. If crystallization was effected in the gel without sedimentation of
the crystals, then the resultant crystals had smooth surfaces without visua
lly detectable surface roughness or asperities viewed by optical microscopy
. The crystals from Carbopol gels also exhibited the uniform shape of an el
ongated tomahawk regardless of the crystallization conditions, in contrast
to crystallization under constant stirring, where the crystal shape of lact
ose changed with crystallization conditions especially as a function of the
initial concentration of lactose. All batches of lactose crystals prepared
from Carbopol gels existed as ol-lactose monohydrate, which showed better
flowability than the controls of a similar particle size.
Conclusions. Crystallization from Carbopol gel produces lactose crystals of
uniform size, regular shape, smooth surface, and improved flowability.