Effect of oil droplet size on the gastric digestion of milk protein emulsions using a semi-dynamic gastric model

Abstract

A small droplet emulsion (SDE) of D4,3 = 0.877 μm and a large droplet emulsion (LDE) of D4,3 = 2.19 μm, containing 3.5 wt% milk protein concentrate and 4.5 wt% sunflower oil, were made. The digestion of the samples was performed using a semi-dynamic model, which simulates the main dynamics of gastric digestion, including gradual acidification, enzyme secretion and gastric emptying. Both SDE and LDE coagulated in 10 min digestion when the pH was ≥5.2. Clots of SDE gradually creamed, but clots of LDE sedimented as shown in light-scattering curves. Confocal images showed a higher inclusion of oil droplets in SDE clots, which later coalesced inside the protein matrix and formed oil pools. Texture analyzer profiles exhibited that clots of LDE were firmer than SDE. The nutrients emptying profile indicated a delay in delivering protein and lipid from SDE digesta while LDE digesta emptied a significantly (P ≤ 0.05) higher amount of protein than SDE at initial gastric emptying points. The absorption of casein micelles to the vast interfacial area of SDE led to the higher association of lipids and proteins, which reduced the clots density and led to the creaming behaviour and late nutrients emptying. The coagulation of casein micelles in LDE formed firm structures that squeezed out soluble proteins and lipids to the serum phase leading to the sedimentation of clots and earlier nutrients emptying. The results shed some light on variations observed in physiological responses in satiety after consuming milk protein emulsions.