On the mechanisms of surface formation and the surface compositions of industrial milk powders

Surface composition of powders is expected to play important role during its end use. Understanding the mechanism of the powder surface formation in terms of the compositional aspect and the ability to control the surface composition will be highly useful in milk powder quality improvement and new product development. In this work, the distribution of milk components in the near surface region of the industrial spray-dried milk powders (skim milk powder and whole milk powder) was studied using electron spectroscopy for chemical analysis (ESCA) combined with the free fat extraction procedures. The results showed that the surface composition is very much different from the bulk composition of powders indicating a kind of solid/solute segregation that must occur during spray-drying, in particular in the period of before a solid crust is formed. This observation has also been supported by theoretical consideration with estimated diffusivity ratios of milk components in liquid.