Buckling and collapse during drying of a single aqueous dispersion of casein micelle droplet

The drying process for dairy products is based on rapid removal of water, quickly concentrating milk components to finally form dry particles. The change in concentration may have a considerable effect on the product structure and influence the final characteristics of the dry material. The aim of this study was to investigate the drying behaviour of a major milk protein, i.e. caseins. The droplet – particle conversion was investigated through a single droplet system and by combining complementary methods. Our results showed that the drying process for caseins comprised three stages involving different evaporation rates and droplet dynamics. A thin layer was formed in the early stage of drying that underwent surface instabilities such as buckling and invagination of the droplet. The drying of caseins led to the formation of a deflated and wrinkled particle shape. These results suggest particular mechanical properties of the casein shell leading to a predictable and a characteristic particle shape.