Characterization of spray-dried whole milk

The chemical surface composition of whole milk powder samples has been estimated by electron spectroscopy for chemical analysis (ESCA). Samples were obtained from a commercial production plant taken at 3 different steps in the process: directly after fluid bed; after separation in the first cyclone and after separation in the second and last cyclone. The powder surface composition of the samples was shown to be similar, except for a slight difference in surface composition for the powder sample taken after the second cyclone. This powder surface was not as uniform, with an increased surface coverage of fat compared to the samples taken earlier in the process. The most probable reason for the increase in fat coverage on these powder surfaces was the mechanical treatment the powder was exposed to during that step. On the other hand, no significant difference was seen for free fat extracted from these powder samples. The chemical surface composition for the whole milk powder produced in the production plant was compared with spray-dried samples from smaller units (pilot scale and laboratory scale). The results showed that the composition of the surface was almost identical for samples dried in the different sized equipment, except for the higher fat coverage for the powder produced in the production plant taken out after the second cyclone. Particle structure, on the other hand, varied between samples manufactured in the different equipment with a larger quantity of small particles in the sample produced in the laboratory spray-drier. Free fat was higher for the powder produced in the laboratory spray-dryer, most likely due to the smaller particle size of the powder.