Overcoming in vitro gastric destabilisation of emulsion droplets using emulsion microgel particles for targeted intestinal release of fatty acids

Whey protein based emulsion microgel particles (9.6 wt% whey protein – 20 wt% sunflower oil) were produced via cold set precipitation using calcium ions (0.1 M) and their behaviour under in vitro gastrointestinal digestion was investigated with conventional oil-in-water emulsions (9.6 wt% whey protein – 20 wt% sunflower oil) as a control. The droplet size distribution, zeta-potential, microstructure and hydrolysis of interfacial whey protein during in vitrogastric digestion and free fatty acid release during in vitrointestinal digestion were compared for both samples. During in vitro gastric digestion, emulsions flocculated and coalesced (d32 ∼ 0.13 μm–∼12 μm after 120 min) due to pepsinolysis of the adsorbed protein layer, as evidenced by SDS-PAGE (sodium dodecyl sulphate polyacrylamide gel electrophoresis). This destabilisation led to uncontrolled and limited release of free fatty acids (44% FFA) during subsequent intestinal digestion, largely due to the reduction in interfacial area. In comparison, emulsion microgel particles were noticeably more stable during in vitro gastric digestion, with only a slight decrease in particle size (d32 ∼ 50 μm–∼20 μm after 120 min). The protection of emulsion droplets against gastric coalescence in emulsion microgel particles was controlled by physicochemical interactions between calcium ions and whey protein in the particles, limiting both pepsin-diffusion and cleavage at the pepsin active site. Under subsequent in vitro intestinal digestion, the microgel particles degraded due to the action of intestinal proteases, releasing fine emulsion droplets, which then gave significantly higher release of free fatty acids (54% FFA).