β-carotene nanoemulsions co-ingested with oatmeal of different viscosities: a semi-dynamic in vitro digestion...

In the present study, the effect of oatmeal concentration and subsequently its viscosity on the colloidal stability, lipid digestibility and bioaccessibility of a β-carotene-loaded nanoemulsion (NE) were assessed during a semi-dynamic in vitro gastrointestinal digestion protocol. The NE:oatmeal mixture at a 10 % (w/w) oatmeal (NE:Oatmeal 10 % (w/w)) concentration presented an initial viscosity of 15.6 ± 1.06 mPa·s while the mixture at a 20 % (w/w) oatmeal (NE:Oatmeal 20 % (w/w)) had a viscosity of 277 ± 5.66 mPa·s. During gastric conditions, the NE:Oatmeal mixtures showed oil droplet destabilization probably due to protein and polysaccharide-lipid colloidal clusters observed in the confocal microscopy images. Nonetheless, the NE:Oatmeal 20 % (w/w) showed a non-gradual viscosity decrease along the successive gastric emptying (GE) steps, which was related to high chyme viscosity values. This had a significant impact on the lipid digestibility and β-carotene bioaccessibility (BA) of the β-carotene-NE during small intestinal conditions. In general, NE:oatmeal 20 % (w/w) presented lower accumulated free fatty acid (FFA) release (34.2 %) than the NE:oatmeal 10 % (w/w) (47.9 %), which was attributed to a limited accessibility of lipid digestive enzymes to the NE droplets. Ultimately, the NE:Oatmeal 20 % (w/w) presented lower β-carotene BA in all the GE compared to the NE:oatmeal 10 % (w/w) due to the lower amount of lipid digestion products contributing to β-carotene micellarization. The findings suggest that meals with higher viscosity, resulting from a greater concentration of nutrients, might reduce fat digestibility and subsequently β-carotene BA. This indicates that food viscosity can modulate nutrient absorption and ultimately food functionality.