Crystallization of Lactose from Carbopol Gels

Abstract

Purpose. To crystallize lactose under static conditions with a view topreparing crystals of well-defined morphology.

Methods. α-Lactose monohydrate was crystallized from neutralizedCarbopol 934 gels. When the majority of crystals had grown to maturity,the gels were acidified using diluted hydrochloric acid and the crystalswere harvested by filtration or centrifugation and washed with ethanol-watermixtures.

Results. Crystals prepared from the gel had a consistently narrowersize distribution than control crystals, prepared from solution underconstant stirring. If crystallization was effected in the gel withoutsedimentation of the crystals, then the resultant crystals had smoothsurfaces without visually detectable surface roughness or asperitiesviewed by optical microscopy. The crystals from Carbopol gels alsoexhibited the uniform shape of an elongated tomahawk regardless of thecrystallization conditions, in contrast to crystallization under constantstirring, where the crystal shape of lactose changed with crystallizationconditions especially as a function of the initial concentration of lactose.All batches of lactose crystals prepared from Carbopol gels existedas α-lactose monohydrate, which showed better flowability than thecontrols of a similar particle size.

Conclusions. Crystallization from Carbopol gel produces lactose crystalsof uniform size, regular shape, smooth surface, and improvedflowability.