Towards spray drying of high solids dairy liquid: Effects of feed solid content on particle structure and functionality

• A micro-fluidic-jet spray dryer was used to fabricate SFD and SD uniform skim milk microparticles.
• Higher feed solid content led to spherical and hollow SD microparticles with less shrinkage.
• The majority of fat enrichment on the surface was during atomization regardless of the feed solid content.
• Larger proportion of protein migration to surface happened during drying, and was retarded by higher feed solid content.
• Higher feed solid content led to SD microparticles of better wettability, but lower solubility.

A micro-fluidic-jet spray dryer was used to fabricate spray freeze dried (SFD) and spray dried (SD) uniform microparticles with feed solid content >30 wt% of reconstituted skim milk. The effects of feed solid content on the particle size, morphology, surface composition, wettability and solubility were investigated. The surface composition of SFD and SD sample was characterized via an X-ray photoelectron spectroscopy. Fat and protein was found to be over-represented on the SD particle surface, while lactose significantly declined. Such ingredient segregation was quantitatively shown to occur during atomization and continue within the drying process, i.e. atomization-induced ingredient segregation (AIIS) and drying-induced ingredient segregation (DIIS). The wettability and solubility of the spray dried samples were quantified using scaled-down GEA Niro Methods in relation to the feed solid contents.