The simulated in vitro infant gastrointestinal digestion of lipid droplets covered with milk fat globule membrane components: The role of interface layers

The interfacial properties of lipid droplets are crucial for infant digestion, yet few studies have explored the impact of the layers of lipid droplets on infant digestion. In this study, four emulsions were prepared: one with milk polar lipids (MPL) serving as the monolayer interface of the lipid droplet (ME-PL), one with MPL and membrane-specific protein (MSP) as the co-monolayer interface of the lipid droplet (ME-Co), one with liposome featuring MPL as the bilayer interface of the lipid droplet (BE-PL), and one with proteoliposome containing MPL and MSP as the co-bilayer interface of the lipid droplet (BE-Co). Cryo-TEM was used to determine the number of lipid droplet interface layers, while confocal laser scanning microscopy confirmed the interfacial distribution. Compared to monolayer emulsions, bilayer emulsions exhibited greater stability. Furthermore, in vitro digestion experiments revealed that BE-Co released free fatty acids the fastest and in the largest amount. During gastric digestion, emulsions with co-components interfaces released fewer saturated fatty acids (SFA) compared to those containing only MPL in the interface, whereas bilayer emulsions released more SFA and polyunsaturated fatty acids (PUFA) than monolayer emulsions. During intestinal digestion, bilayer and co-interfacial emulsions released more SFA and less unsaturated fatty acids (USFA), with BE-Co releasing the highest percentage of SFA (87.11 ± 0.10 %) and the lowest percentages of USFA, specifically 2.95 ± 0.00 % PUFA. This study introduces a novel preparation method that uses a bilayer interface to simulate the human milk globule interface and explores the effect of different interface layers on lipid droplet characteristics, providing valuable insights for the development of infant food.