Effects of freeze drying and spray drying on the microstructure and composition of milk fat globules

Abstract

Freeze drying and spray drying are conventional methods for converting milk into powder in the dairy industry. The purpose of this study was to investigate the effects of these drying methods on the physical, chemical and structural features of milk fat globules (MFGs). The globule sizes increased after freeze drying and spray drying, but the integrity of their microstructures was still maintained. Compared with that in untreated MFGs, the composition of the fatty acids underwent fewer changes under the two different drying conditions. The main phospholipids showed some differences between the freeze-dried milk and spray-dried milk, and the saturation of the fatty acids of phospholipids was increased after the drying treatments. A reduction in the cholesterol content was observed after the freeze-drying and spray-drying processes. The level of unsaturation decreased as the diameter of the globules increased. The results indicated that freeze drying had a significant effect on the liquid-ordered domains in the MFG membrane, which was formed by sphingolipids and cholesterol. However, spray drying influenced the liquid-disordered domains, which were formed by glycerophospholipids. Thus, the drying method appears to affect the physical, chemical and microstructure characteristics of MFGs, which may affect the stability of the globules in milk and the way the milk is digested.