Tuning the rheological properties of protein-based oleogels by water addition and heat treatment

Although mostly known for their gelling ability in water, proteins can also be used to structure oil into so-called oleogels. To create these oleogels, protein aggregates (d ∼190 nm) were formed by heat treatment in an aqueous environment and then suspended in oil using a solvent exchange procedure. To control the interactions between colloidal protein aggregates in oil, the effect of the addition of a small amount of water and the application of a heat treatment were investigated. Addition of water was shown to induce clustering of the protein aggregates. The effect of increased particle clustering was observed up to water addition in the amount of 0.5 g water/g protein, above which free water droplets were formed. As a result of water addition, G′ increased dramatically by up to three orders of magnitude. Besides an increase in G′, also an increase in critical strain and yield stress was observed. Moreover, the gels became responsive to temperature when water was added. G’ increased even further upon heating, and regained gel strength upon cooling due to enhanced particle-particle interactions. We propose that these interactions are most likely due to the formation of capillary bridges between the protein aggregates. Addition of water and subsequent heat treatment are thus effective ways to increase the interactions between protein aggregates. This simple approach forms an interesting route to tune the rheological properties of protein oleogels.