Microstructure evolution of micellar casein powder upon ageing: Consequences on rehydration dynamics
Résumé
Micellar casein (MC) powder must be completely dispersed and dissolved in water to fully exhibit their
functional properties. However, the rehydration properties of these powders decline strongly during
storage, leading to loss of solubility and longer rehydration time. In this work, controlled ageing was
applied to a MC powder in order to better understand the mechanisms responsible for the deterioration
of rehydration properties in the course of storage. The objective was to investigate evolutions of powder
surface structure and composition as well as the link between these changes and the decline in rehydration
properties, which were evaluated through characteristic times of different steps constituting the
full rehydration process. Lipid migration (towards the particle surface) and increase of interactions between
surface micellar particles during storage were proven to be responsible for major changes in
different rehydration stages. First, the delay in water penetration into particles was quantified; then, the
increase of particle fragmentation time was determined and finally, an extended total rehydration time
was evidenced. Analysis of the characteristic times of different rehydration stages shows unambiguously
that the main step increasing the total rehydration time of aged powder is not lipid migration but the
crosslink formation during storage, which can thus be considered as the rate-limiting stage for rehydration
of aged powder.