Perspective: Margarine as an emulsion-filled colloidal oleogel

Common margarine is a semi-solid water-in-oil emulsion, where the continuous phase is a plastic polycrystalline colloidal oleogel composed of aggregated nanoplatelets of crystallized triacylglycerols (TAGs). TAG nanocrystal platelets nucleate, grow, and aggregate into clusters, which then form a fractal colloidal network of polycrystalline particles, trapping liquid TAGs in this fat crystal network. This hierarchical structure is very sensitive to external temperature and shear fields, which affect everything from crystalline nanoplatelet (CNP) size to the aggregation of such CNPs into larger clusters. Ultimately, structure affects the mechanical properties, oil binding, and plasticity of such industrially relevant materials. Here, we review some of the history of margarine, its quality characteristics, and its uses. We also describe the structure of margarine and relate it to macroscopic functionality, which is given mainly by the structure of the fat crystal network in the continuous oil phase. The concept of the yield stress of a fat as the most global indicator of functionality is discussed in light of quantitative physical models developed, which allow for the exact calculation of the yield stress. By understanding the effects of crystal size, strength of intermolecular interactions, amount of solid crystalline mass present, and the spatial distribution of such crystalline mass within the network, it is possible to engineer functionality and optimize performance. The structural complexity of such common food highlights the need for an in-depth understanding of the physics of such soft materials for manufacturing optimization as well as for engineering new structures with novel macroscopic properties.