COMPOSITION AND STRUCTURE OF DEMINERALIZED SPRAY-DRIED MILK PERMEATE POWDER

Permeates obtained by the ultrafiltration of milk were demineralized b y electrodialysis to demineralization rates (DR, expressed in %) varyi ng from 51 to 93. The demineralized permeates were then concentrated t o 55% total solids, cooled to 12-degrees-C to crystallize lactose, and spray-dried. 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 h ighest at DR of 51 and was lowest at DR of 93. The sharp-edged particl es were lactose crystals covered with dried collapsed foam consisting of the mother liquor. The globular particles were formed by minute lac tose crystals cemented by amorphous material. X-Ray microanalysis (ele mental 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 alpha-monohy drate crystals (ratio of alpha-monohydrate to amorphous lactose was 2. 8:1), made the permeate powders resistant to the effects of an atmosph ere at 85% relative humidity. Recrystallization of lactose and disinte gration of the globular particles occurred only in powders exposed to 100% relative humidity.