Kinetic effects on interfacial partitioning of fat crystals

• Both thermodynamic and kinetic effects influence the orientation of fat crystals at an o/w interface.
• Increasing surfactant concentration causes crystals formed in a fat globule to partition to the aqueous phase.
• Slower crystallization rate increases the likelihood that fat crystals will partition from the fat globule into the aqueous phase.

Fat crystals, like other colloidal particles, can influence the stability of food emulsions. Unlike colloidal particles added to form Pickering emulsions, however, crystals form within food emulsion droplets via crystallization and then the crystal wettability determines its ultimate partitioning relative to the oil–water interface. Most descriptions of crystal partitioning assume the final interfacial state of fat crystals can be predicted by key system properties like interfacial tension and contact angle. However, recent work has shown the kinetics of interfacial particle adsorption can be surprisingly slow as a result of variables like particle roughness as well as internal droplet rheology. This work examined the effects of common variables, normally not thought to control crystal partitioning, on the state of crystals in a milkfat emulsion. For example, crystallization dynamics, tuned by varying surfactant adsorption and the crystallization driving force, are found to alter interfacial partitioning of milkfat crystals at oil–water interfaces. Slower crystallization rates increase the likelihood that crystals will leave the droplets by dewetting and reside in the aqueous phase, even with no compositional changes. The tendency of fat crystals to dewet the liquid oil increased as the oil–water interfacial tension, and the contact angle of aqueous surfactant on fat crystals, decreased. Several possible explanations for the results observed are postulated.

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