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). Samp les were obtained from a commercial production plant taken at 3 differ ent steps in the process: directly after fluid bed; after separation i n the first cyclone and after separation in the second and last cyclon e. The powder surface composition of the samples was shown to be simil ar, except for a slight difference in surface composition for the powd er 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 han d, no significant difference was seen for free fat extracted from thes e 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 res ults showed that the composition of the surface was almost identical f or samples dried in the different sized equipment, except for the high er fat coverage for the powder produced in the production plant taken out after the second cyclone. Particle structure, on the other hand, v aried between samples manufactured in the different equipment with a l arger quantity of small particles in the sample produced in the labora tory spray-drier. Free fat was higher for the powder produced in the l aboratory spray-dryer, most likely due to the smaller particle size of the powder.