CHANGES IN SURFACE-COMPOSITION OF SPRAY-DRIED FOOD POWDERS DUE TO LACTOSE CRYSTALLIZATION

The surface composition of spray-dried lactose-containing powders was estimated by electron spectroscopy for chemical analysis (ESCA), and p article structure was studied by scanning electron microscopy before a nd after storage in a humid atmosphere. The surface composition of dry powders made from lactose/sodium caseinate solutions was nearly ident ical to that of powders stored at 75% relative humidity for 4 d. Prote in started to dominate the powder surface even when it was present at only low solution concentrations. The particle structure after storage in a humid atmosphere was completely changed even though the surface composition remained relatively unchanged. When soybean oil emulsions with sodium caseinate and lactose were spray-dried, protein was over-r epresented on the powder surface. If the protein concentration was suf ficiently high, the fat was almost completely encapsulated. In the cas e of the powders with high lactose content almost total release of the encapsulated fat on the powder surface was observed after storage in a humid atmosphere. When the lactose concentration was lower, release of fat on the powder surface was less pronounced. The structure of fat -containing powders was studied by scanning electron microscopy. Befor e storage in a humid atmosphere, particles were discrete with smooth s urfaces. As the fat was released onto the powder surface, the powder b ecame lightly agglomerated and attained a smooth structure.