Clustering of oil droplets in o/w emulsions enhances perception of oil-related sensory attributes

The sensory perception of o/w emulsions is determined by their structure and physicochemical properties. The aims of this study were (a) to determine the influence of oil droplet clustering in o/w emulsions on sensory perception and (b) to link their sensory attributes to rheological, tribological and structural properties. Clustered emulsions were prepared by combining o/w emulsions stabilised by different sets of emulsifiers: (a) positively-charged gelatine and negatively-charged whey protein (WPI), and (b) positively-charged gelatine and negatively-charged diacetyl tartaric acid ester of mono- and diglycerides (DATEM). Oil droplet clusters ranging in diameter from 1 to 50 μm were obtained. The difference in charge density between gelatine- and DATEM-stabilised oil droplets was higher than that between gelatine- and WPI-stabilised droplets. This difference allowed to alter the interaction strength within oil droplet clusters. The sensory perception of clustered emulsions was quantified using the Rate-All-That-Apply (RATA) methodology with untrained subjects (n = 83). Participants assessed o/w emulsions varying in cluster size (1 μm–50 μm), cluster strength (tuned by changing the emulsifier-pairs), and single droplet emulsions with and without adjusted viscosity, as well as a reference emulsion with large single droplets (comparable in size to emulsions with large clusters). Creaminess and thickness intensities were significantly higher for clustered o/w emulsions compared to that of single droplet o/w emulsions with the same oil content and similar oil droplet/cluster size. With increasing cluster size, creaminess and thickness intensities increased significantly for hetero-aggregated clusters with weak interactions (gelatine-whey protein). When cluster interactions were stronger (gelatine-DATEM), creaminess intensity increased to a lesser extent and grittiness intensity increased considerably. Thickness and creaminess were strongly correlated to the rheological (e.g. consistency) and tribological properties (e.g. fiction coefficient at 10 mm/s) of o/w emulsions with clustered oil droplets. Grittiness and fattiness were strongly correlated to the tribological properties (slope of mixed regime) of o/w emulsions and their interactions with saliva. We conclude that clustering of oil droplets in o/w emulsions by hetero-aggregation allows to enhance the sensory perception of fat-related attributes by tuning rheological and tribological properties, and provides an effective method to structure liquid foods to obtain specific sensory properties.