THE SURFACE-COMPOSITION OF SPRAY-DRIED PROTEIN LACTOSE POWDERS

The surface composition of spray-dried mixtures of lactose-protein and lactose-glycine were estimated by means of electron spectroscopy for chemical analysis (ESCA). The results show that even with a low concen tration of protein (0.01 wt.%) in the solution to be dried, protein st arts to appear on the surface of the powder. At a protein/lactose rati o of 1/99 the protein starts to dominate the powder surface. At a prot ein/lactose ratio of 20/80, about 70% of the surface is covered by pro tein. The results are similar for the proteins sodium caseinate and bo vine albumin. The spray drying of mixtures of lactose and glycine give s a different result. In this case, the surface composition of the pow der reflects the composition of the mixture to be dried. The surface t ensions of the solutions show that the proteins have a higher surface activity than lactose, since even a small amount of protein added to a lactose solution lowers the surface tension considerably. Glycine aff ects the surface tension only to a minor extent. These results show th at the composition of the air-water interface of the drying droplets i s reflected in the surface composition of the dried powder. In additio n, scanning electron micrographs show that the changes in the powder s tructure when protein is added to the solution are associated with the presence of protein on the surface. When the surface coverage of prot ein increases, dents start to appear in the particles. The powders mad e from lactose-glycine solutions are highly agglomerated regardless of the glycine concentration.