In vitro digestibility of O/W emulsions co-ingested with complex meals: Influence of the food matrix

Oil-in-water (O/W) emulsions are promising delivery systems of lipophilic bioactive compounds into meals composed mainly of water. The colloidal stability of β-carotene-loaded O/W emulsion incorporated into whole milk, oatmeal and whole milk-oatmeal meals. Their subsequent gastric emptying rate, lipid digestibility and β-carotene retention during in vitro gastrointestinal digestion were evaluated using a semi-dynamic gastric model followed by a static small intestinal model. The dispersed particles within the meals, lipid droplets, casein micelles as well as protein and β-glucan aggregates, were responsible for the bigger average particle sizes of both O/W-oatmeal and O/W-whole milk-oatmeal (13.07 ± 1.81 and 7.60 ± 1.21 μm, respectively) compared to the O/W emulsions and O/W-whole milk (0.56 ± 0.03 and 0.44 ± 0.04 μm, respectively). Semi-dynamic in vitro gastric digestion of O/W-whole milk showed lipid droplets embedded into an insoluble protein network emptied earlier than the O/W emulsion. Conversely, O/W-oatmeal and O/W-whole milk-oatmeal had delayed lipid emptying, probably because of the gelation of the β-glucan from oats. During the in vitro small intestinal digestion, the rate of the FFA release was linked to the gastric emptying rate. Indeed, both O/W emulsion and O/W-whole milk presented an exponential increase in the FFA release, whereas the O/W-oatmeal and O/W-whole milk-oatmeal followed a stepwise trend. The β-carotene retention during in vitro gastrointestinal digestion depended on the lipid amount at each digestion time moment. Hence, this work provides valuable insight into the behaviour of O/W emulsions incorporated into meals and during their subsequent in vitro gastrointestinal digestion.