Lorenzo Metilli, Megan Povey, Aris Lazidis, Stephanie Marty-Terrade, and Elena Simone
University of Leeds, UK
Due to the increasing rates of obesity worldwide and following concerns from health institutes and consumer associations, the design and manufacture of healthier products with reduced caloric content is of great importance. An effective solution to reduce caloric content involves air incorporation within food products, which also provides changes in texture and mouthfeel. In the case of fat-based products, aerated oils (also termed oleofoams) represent a novel yet promising materials that suit this purpose. Oleofoams contain gas bubbles stabilized by a dispersion of fat crystals in a continuous vegetable oil phase, through a Pickering mechanism. Crystal properties such as shape, size distribution and polymorphism affect the microstructure of the aerated material, its rheological properties and stability against coalescence and oil drainage. To promote the use of oleofoams in industry, it is pivotal to gain understanding of these novel systems, in particular how starting materials and the processing conditions affect the final microstructure. In this work, a model fat system was crystallized to form a semisolid matrix (oleogel), which was subsequently aerated to generate an oleofoam. The crystallization and aeration processes were monitored using in situ light turbidimetry and a bespoke ultrasonic velocimetry probe. Both oleogels and oleofoams were characterized with a set of off-line techniques, such as X-ray diffraction, differential scanning calorimetry, optical microscopy and rheology, in order to correlate the processing conditions to final product properties. Results show that oleogels contain a dispersion of β(V) cocoa butter nanoplatelet crystals which stabilize the air bubbles during the aeration step. The corresponding oleofoams reached in average a 200% increase in volume, with high stability to oil drainage.