Behaviour of whey protein emulsion gel during oral and gastric digestion: effect of droplet size

A set of whey protein stabilized-emulsion gels with different droplet size distributions (D-4,D-3 = similar to 1, 6 and 12 mu m) was produced, and the mechanical properties of the gels in the linear viscoelastic region and at large deformation were measured, along with the physicochemical and structural changes of the gels during oral mastication and gastric digestion. The gels containing 1 mu m oil droplets had an aggregated particle structure with proteins coating at oil droplets whereas the gels containing 12 mu m oil droplets had a particle-filled structure with spatially continuous matrix. During oral processing, the release of oil droplets from the gels increased as the droplet size increased, with coalescence being seen in gels containing oil droplets of 6 and 12 mu m diameter. Under gastric digestion, high degrees of coalescence and phase separation of oil droplets occurred in the gels containing 6 and 12 mm oil droplets because of oil droplet release from the gel matrix; this led to slow gastric emptying. The gels were finally broken down into peptide aggregates and oil droplets (or free oil). The gels, containing 1 mm oil droplets disintegrated into various particles of several to several tens of microns with a low degree of oil droplet release and coalescence. Protein breakdown was slower in these gels, suggesting that the protein structures of the gel matrices were affected by the sizes of the incorporated oil droplets.