Investigation of the microstructure of milk protein concentrate powders during rehydration: Alterations during storage

Field emission scanning electron micrographs of fresh milk protein concentrate powder particles after rehydration for 10min: A) initial spray-dried powder particle; B) rehydrated powder particle; C, D) details of the surface of rehydrated powder particles at 2 magnifications (× 50,000 and × 100,000). The black arrows in panel A indicate the presence of ∼100-nm holes and surface roughness. The white arrows in panels C and D indicate the presence of intermicellar bridges.

Field emission scanning electron micrographs of fresh milk protein concentrate powder particles after rehydration for 80min observed at different magnifications: A) ×4,500; B) ×7,500; C) ×3,000; and D) ×18,000.

Field emission scanning electron micrographs of aged milk protein concentrate powder particles after 2-mo storage at 20°C and water activity of 0.23: A) spray-dried powder particle; B, C) hydrated powder particle after rehydration for 10min; D) details of the surface of the rehydrated powder particle (×50,000) observed in panel C.

Field emission scanning electron micrographs of aged milk protein concentrate powder particles after rehydration for 80min observed at different magnifications: A) ×4,300; B) ×5,000; C) ×1,800; and D) ×2,500. The arrow indicates part of the crust undergoing disruption.