Emulsion flocculation induced by saliva and mucin

Upon consumption of emulsions, mixing with saliva occurs. This article shows that whole saliva and a model mucin (pig gastric mucin, PGM) are able to induce extensive droplet flocculation. Saliva samples collected from several subjects at different times of the day always showed flocculation. However, there was a clear variation between samples from different individuals with respect to the structure of the flocs and reversibility of flocculation upon dilution. Several aspects of PGM-induced flocculation, measured by microscopy, particle size analysis, demixing experiments and rheology pointed to depletion flocculation as the main mechanism of flocculation. However, although depletion may also be an important driving force in saliva-induced flocculation, the required mucin concentration seems to be considerably lower than for PGM. Therefore other interactions, such as bridging or specific binding, may be important as well. The observed aggregation is expected to have implications for understanding sensory properties of emulsions. The viscosities of emulsions measured in vitro in the absence of saliva may deviate from the in vivo viscosities relevant for sensory perception, especially in case of liquid emulsions in which the droplets are not flocculated, such as milk