Effect of Droplet Size on the Properties of Spray-Dried Whole Milk

Abstract

The droplet size of the whole-milk concentrate spray formed by wheel atomization strongly affects the drying characteristics of the whole-milk powder particles. The droplet size depends on the viscosity of the concentrate. The concentrate viscosity can be changed by varying the pre-heat treatment of the milk (denaturation of whey protein), the dry matter content and by the homogenization pressure. By homogenization the fat globules are divided into smaller globules with new surfaces which are occupied by the protein present in the concentrate. As a consequence of homogenization the apparent volume fraction of the fat-protein complexes increases.

In this study it was found that the particle size of the powder is a function of the basic viscosity of the concentrate (i.e. the viscosity obtained by extrapolation to infinite rate of shear). We expect that the basic viscosity is relevant, since at the wheel there exists a very high rate of shear. Increasing the basic viscosity of the concentrate results in an increased moisture content of the powder, a drop in the free fat content and a rise in the insolubility of the powder. This last may be explained by the fact that larger particles spend a longer time in the critical moisture range in which heat damage to the protein may occur.