Surface tension-driven effects in the reconstitution of food powders

Quick powder reconstitution is generally necessary for consumer acceptance of dehydrated food materials; thus, an improved understanding of the mechanisms preventing complete reconstitution can help aid the discovery of solutions to improve product quality. Among the steps of reconstitution (wetting, sinking, dispersing, and dissolving), the “sinking” step is often described in the literature as being inhibited by a high surface tension, keeping particles afloat, insinuating that a reduced surface tension of the medium would improve sinking and thus overall reconstitution.

In the current study, the sinking of food powders maltodextrin and whole milk powder were observed in an axially stirred vessel. Experiments were performed both in demineralized water (surface tension γ = 72 mN m−1) as well as in demineralized water with the surfactant polysorbate 20 added to its critical micelle concentration (CMC), with a surface tension γ = 32 mN m−1.

Contrary to the scientific literature, the sinking behavior of the bulk powder was markedly worse when the liquid surface tension was lower. This can be explained due to the reduced capillary penetration into a porous powder bed when the surface tension is reduced. Thus in the scope of the sinking step of powder reconstitution, the powder must not be considered as individual particles, but rather as a porous capillary bed where capillary and resultant waterlogging drive the “sinking” step, particularly when developing physical models to predict the reconstitution behavior of powders.