Surface composition of industrial spray-dried milk powders. 1. Development of surface composition during manufacture

Development of the surface composition of milk powders during manufacture was investigated in three industrial spray-dried milk powders (skim milk powder, whole milk powder and instant whole milk powder). Samples were obtained from commercial production plants and were collected at different manufacturing stages. As the powder properties of milk powder are defined in spray-drying and the subsequent manufacturing processes, the powder samples were collected at the exit of the spray drying chamber and the exit(s) of the fluidized bed(s), and the surface compositions of the powder samples collected were studied using electron spectroscopy for chemical analysis (ESCA). For all three industrial spray-dried milk powders, no significant differences in surface composition were observed between the samples collected at different manufacturing stages, except for a slight increase (3%) in the surface fat coverage for whole milk powder after the fluidized bed drying process. These results indicate that the surface composition of milk powders is determined to a large extent during the spray drying process and that the subsequent fluidized bed drying and handling processes have no or little effect on the surface composition of milk powders. even though these processes affect the final powder quality (e.g. moisture content, particle size). For whole milk powder and instant whole milk powder, no fat appeared to leak out on to the powder surface during the fluidized bed drying process; however, the fat present on the powder surface after the spray-drying process appeared to flow over the particle surfaces, resulting in a slight increase in the surface fat coverage. After lecithin treatment (instantization), because a mixture of lecithin and anhydrous milk fat was sprayed on the powder, a slight increase in the thickness of the surface fat layer was observed. (C) 2008 Elsevier Ltd. All rights reserved.