Characteristics of Milk Powders Produced by Spray Freeze Drying

Abstract

Skim and whole milk powders were manufactured at lab scale by spray freeze drying (SFD), using liquid nitrogen as the cryogen. The polydispersity of droplet/particle sizes was limited using an encapsulator nozzle to atomize the feed. Particle morphology was examined using a scanning electron microscope. Samples were compared with equivalent spray-dried powders in tests of wettability and dissolution in water. The spray freeze-dried powders were found to be highly porous, with a uniform structure of pores throughout the entire particles. When tested in water, SFD skim milk powders wetted roughly three times as fast as industrially spray-dried agglomerated skim milk powders and were observed to dissolve rapidly by breaking down into smaller particles.

Keywords:

• Dairy powder
• Porosity
• Spray freeze drying
• Wettability

ACKNOWLEDGEMENTS

The authors thank Hortresearch Ltd., New Zealand, for allowing the use of their facilities and providing help and expertise on the project. We are particularly appreciative of Tim Holmes, for his photography services, and Dr. Danyang Ying, for his cooperation.

Samuel Rogers gratefully acknowledges the financial support from the Geoffrey Gardiner Foundation and Dairy Innovation Australia. Winston Duo Wu thanks the Australian Research Council for his Ph.D. scholarship and an International Fee Scholarship from the Department of Chemical Engineering, Monash University.