Microstructure of whole milk powder and of insolubles detected by powder functional testing

The functional properties of whole milk powder (performance during reconsti tution in water and coffee) are routinely measured to determine powder qual ity. An examination of the microstructure of milk powder and of the insolub le material collected after applying a series of functional tests provided insight into why the insoluble material formed during reconstitution. The microstructures (transmission electron microscopy and confocal microsco py) of four commercial whole milk powder samples and of the insoluble mater ial produced during functional testing were assessed. The microstructure of the whole milk powder could be related to features observed in the microst ructure of some of the insolubles collected after powder functional testing . It is likely that heating conditions throughout the powder manufacturing process resulted in the denaturation of beta-lactoglobulin and its interact ion with other proteins and fat globule membrane components, thus influenci ng the solubility of the milk powder. The application of shear during proce ssing resulted in the greatest change to powder solubility in this study. I ncreasing homogenisation pressure during processing resulted in fat globule size reduction, adsorption of casein micelles to the fat globule membrane, and the formation of clusters of fat globules caused by the sharing of ads orbed casein micelles. The presence of large numbers of these clusters in t he milk powder increased the formation of insoluble material during powder reconstitution in water and coffee.