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a b s t r a c tPhase separation of insoluble particles, so called "white flecks", is a physical defect in reconstituted milk obtained from spray-dried, fat-containing dairy powders. Compared with bulk powder particles, white flecks have quite different chemical and morphological characteristics. They consist mainly of proteins and fat, forming a dense network. Here, two concurrent formation mechanisms are suggested based on the structures revealed by confocal microscopy imaging. Fused spherical particles with free fat on the surface were the most abundant and likely formed during the manufacturing process. Sharp-edged particles containing shapes typical of lactose crystals formed during storage. Fat globule stability was thus determined to be critical in preventing white fleck formation. Stability was increased with (a) the presence of lecithin in the oil phase; (b) systems with high protein-to-fat ratio and (c) storage in dry conditions since humidity leads to lactose crystallisation and disruption of the fat globules in powders.

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Changes in cheese production processes may have a significant effect on subsequent whey composition and functionality. To control these changes is important since whey is commonly processed into ingredients used in numerous applications in the food industry. In this study, the characteristics of 4 demineralized whey powders (DWPs) were studied. DWPs were produced from partially high-temperature heat-treated (HH), ultrafiltered (UF), or ultrafiltered high-temperature heat-treated (UFHH) milk. DWP produced from pasteurized milk was used as a reference (REF). All experiments were carried out on industrial scale. The quantity of nonprotein nitrogen (NPN) in total protein (TP) was elevated by HH, and reduced by UF treatment. Whey protein content of whey was significantly elevated by UF, but reduced when HH treatment was applied. The volume and total solids of UFHH whey were significantly reduced compared to REF and HH wheys, but the chemical composition was comparable. There were no significant differences in the degree of denaturation, viscosity, water-binding capacity, emulsifying capacity, or emulsion stability of the DWPs, but heat stability was significantly elevated by UF treatment.