Novel approaches to oil structuring via the addition of high-pressure homogenized agri-food residues and water forming capillary bridges

The suspension of micronized agri-food residues, such as tomato peels and spent coffee grounds, at 25% vol in peanut oil, results in the formation of a sample-spanning network (capillary suspension) upon the addition of a secondary immiscible fluid, such as water (at 0.17–0.57 vol with respect to the oil), to preferentially wet the particle surface, thus forming capillary bridges. The strength of the capillary bridges, measured through the rheological characterization of the structured oil suspensions, depends on (a) the surface properties of the particles (in both cases prevalently hydrophilic, with the three-phase contact angles < 90°), (b) the fraction of added water, and (c) the mean particle size of the residues. In fact, the suspensions prepared with high-pressure homogenized particles (70 MPa, 3 passes) exhibit an apparent yield stress more than one order of magnitude higher than those prepared with coarser, high-shear mixed particles (>100 Pa vs. < 10 Pa). Finally, also the addition of a surfactant to the water phase dramatically affects the formation of the capillary bridges, reducing the interfacial tension at the oil/water interface. These results suggest a potential alternative route to vegetable oil structuring, to develop innovative foods and food ingredients based on low-calorie, health-beneficial agri-food residues, which not only induce the formation of a oleogel structure, but which also replace a fraction of the lipids.