Tailoring the digestion of structured emulsions using mixed monoglyceride–caseinate interfaces

The destabilisation of emulsions within the stomach alters their droplet size and surface area, which in turn influences the rate and extent of fat digestion. In this study, we sought to gain further understanding of the mechanisms of the colloidal destabilisation of emulsions during digestion by examining how the composition of the interface impacts on these destabilisation processes. Understanding of emulsion destabilisation within the stomach was then linked to the extent of fat digestion through in vitro lipolysis measurements and in vivo triglyceride absorption studies. Two factors were examined; 1) co-variance of protein and monoglyceride composition at the droplet surface and 2) fat phase composition. Of the two emulsifiers present, caseinate provided the colloidal stability to the emulsion via a combination of electrostatic and steric repulsion. The acidic pH of gastric fluid resulted in a loss of electrostatic charge and a collapse of the casein steric layer, ultimately causing the emulsion to flocculate. The presence of monoglyceride influenced the emulsions susceptibility to flocculation in gastric juice and the resistance of the interface to film rupture which impacted the degree of droplet coalescence. It appeared that there was an optimum ratio between monoglyceride and protein at the interface for emulsion destabilisation. An excessive decrease in protein at the interface as monoglyceride concentration increased limited initial droplet flocculation, because there were fewer junction points for protein bridging between droplets. These changes to emulsion droplet structure had an impact on the in vitro rate and the extent of lipolysis. However triglyceride absorption in vivo was only significantly impacted when the coalesced droplet structure (e.g. emulsion containing solid fat) was maintained until the intestine. The principle cause of the altered lipolysis profile was the destabilisation of the emulsion within the stomach. These results highlight that the complexity of real food systems (i.e. multiple/mixed ingredients) can have an important impact on the digestion of emulsions, and have implications for the creation of functional foods aimed at obesity and/or diabetes.