In vitro digestion of emulsions: mechanistic and experimental models

Digestion is a complex combination of physical, chemical and biological processes. In order to investigate the impact of food structure on the digestion of lipids, we work on a controllable triglyceride-based system: emulsion. In this study, the emulsion was composed of a single triglyceride (tricaprylin or triolein), decanal as a model lipophilic micronutrient, and a single emulsifier (beta-lactoglobulin or sodium oleate) at different concentrations. We investigated the effects of these parameters on an in vitro intestinal static digestion, which was monitored using classic physicochemical methods: fatty acid titration, lipids extraction/chromatography and sizing. To interpret the results, we developed several mechanistic models based on mass transfer kinetics, which enable a direct comparison and identification of the factors influencing the digestion. These factors are the molar mass of the lipids, the initial interfacial area (droplet size) and dispersed volume fraction, the interfacial tension and dilatational viscoelasticity. We also developed an experimental digestion model based on a single droplet using tensiometry. This technique was able to monitor the kinetics of lipolysis and micellar solubilization simultaneously. All methods confirmed the result from our previous study that the type of triglyceride is the major parameter influencing the digestion. Moreover, the mechanistic and experimental models proved that digestion was usually faster for beta-lactoglobulin emulsions/droplets compared to the sodium oleate ones. There was no clear effect of the emulsifier concentration.