The morphology and internal composition of dried particles from whole milk—From single droplet to full scale drying

Abstract

Powder structure and functionality are expected to be closely linked to the composition and drying process. In order to understand the optimization of the quality of a powder, e.g. encapsulation efficiency, or wetting and dispersion properties, monitoring of the particle microstructure is an attractive concept. However, to study the impact of different parameters in formulation and drying process on full scale is complicated and expensive, hence, studies on smaller scale, even single particle drying, is a potentially useful complement, as long as the results are comparable. The aim of this study is to compare morphology and internal composition of whole milk particles produced at different dryer scales to assess the development of internal structure in powder formed by spray drying. Whole milk was spray dried in the single particle dryer, laboratory dryer, pilot plant dryer and full scale dryer. The morphology and composition of the particles obtained were analyzed by low vacuum-SEM, confocal Raman microscopy and X-ray photoelectron spectroscopy. Phenomena such as adsorption of surface active compounds at the particle surface and phase segregation are observed to different extent, depending on particle size and drying time. The scale of drying influences the internal microstructure and distribution of components in the particles, and to a small extent also the external morphology. These effects are proposed to be related to the drying times for different droplet sizes, although mechanical handling effects and agglomeration in the full scale dryer may also influence the final morphology of these particles, as well as the surface composition.