Composition and Structure of Demineralized Spray-Dried Milk Permeate Powder

Permeates obtained by the ultrafiltration of milk were demineralized by electrodialysis to demineralization rates (DR, expressed in %) varying from 51 to 93. The demineralized permeates were then concentrated to 55% total solids, cooled to l2°C to crystallize lactose, and spraydried. Light microscopy and scanning electron microscopy showed that the resulting powders consisted partly of globular and partly of sharp-edged particles. The proportion of the globular particles was highest at DR of 51 and was lowest at DR of 93. The sharp-edged particles were lactose crystals covered with dried collapsed foam consisting of the mother liquor. The globular particles were formed by minute lactose crystals cemented by amorphous material. X-Ray microanalysis (elemental analysis and mapping for potassium, calcium, and phosphorus) of the powders showed that the mineral elements were concentrated in the globular particles. Lactose, being mostly in the form of a-monohydrate crystab (ratio of a-monohydrate to amorphous lactose was 2.8:1), made the permeate powders resistant to the effects of an atmosphere at 85% relative humidity. Recrystallization of lactose and disintegration of the globular particles occurred only in powders exposed to 100% relative humidity