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Many foods with a high palatability include significant quantities of fat. Fat influences next to the sensory perception and palatability also the microstructure of foods. It is thus challenging to reduce the fat content in many food items without negative impact on texture or perception. Fats and oils are mostly found as droplets in both solid and liquid matrices. Those droplets can be distributed homogeneously or inhomogeneously throughout a system. Previous research has shown that inhomogeneity (clustering) in the distribution of fat, in model systems, changes the fat related sensory perception and changes the mechanical properties. However, so far, the processes to obtain an inhomogeneous (clustered) fat distribution neither allow control over the process nor incorporation into foods.Therefore, this research aimed to understand the influence of fat phase inhomogeneity through controlled clustering of oil droplets on physical-chemical properties (rheology, tribology, cluster morphology), in-mouth behaviour and sensory perception of liquid o/w emulsions, emulsion gels and emulsion-filled gels. The findings of this research can help to control the microstructure of foods to design the physicochemical and sensory properties of foods. Further, the insights might help in reducing the fat content of foods without negative impact on mechanical properties and sensory perception. Key conclusions/findingsOil droplet cluster size and interaction strength (within oil droplet clusters) can be controlled in liquid o/w emulsions, and semi-solid emulsion filled gels.Two methodologies provide good control over the size and interaction strength: hetero-aggregation and clustering with cross-linkers. For hetero-aggregation, the cluster size is controlled by the volume ratio of charged droplets and the strength by the charge of the emulsifier. For chemical clustering, the extent of clustering depends on cross-linker content. With regards to oil droplet inhomogeneity in gels, thi

Clustering of oil droplets changes the rheological properties of oil-in-water (o/w) emulsions and can be used as a tool to structure foods. The aim of this study was to manipulate both oil droplet cluster size and cluster strength in liquid o/w emulsions, and to investigate the effect of these parameters on the rheological properties. Clustered emulsions were prepared using three different methods: (i) clustering by protein-proanthocyanidin interactions, (ii) clustering by hetero-aggregation of oppositely-charged emulsion droplets, and (iii) enzymatic clustering of protein-stabilised droplets using transglutaminase. Clustering by protein-proanthocyanidin interactions allowed to control oil droplet cluster size from 1 to 140 μm. Clusters decreased in size upon both an increase and decrease in pH, but were stable against changes in ionic strength. Hetero-aggregation of oppositely-charged oil droplets (gelatine/whey protein and gelatine/DATEM) allowed to control cluster size from 1 to 40 μm. Clusters showed a strong decrease in size in response to changes in pH and a small decrease in size with increasing ionic strength. Enzymatic clustering did not allow to control cluster size. Cluster strength of proanthocyanidin-stabilised clusters was found to be higher than that of hetero-aggregated clusters. Stabilisation of clusters was likely induced by different protein-proanthocyanidin interactions such as H-bridges, π-π stacking, and hydrophobic interactions, whereas hetero-aggregation is based on electrostatic interactions. Upon clustering, emulsion viscosity increased by up to three orders of magnitude. We conclude that protein-proanthocyanidin interactions and hetero-aggregation are effective methods to tune droplet cluster size and strength in o/w emulsions, and that cluster size and interaction strength control the rheological properties of o/w emulsions with clustered oil droplets.