Regulating the lipid droplet interface based on milk fat globule membrane and milk proteins to improve lipid digestion of model infant formula emulsion

The interfacial properties of lipid droplets play a crucial role in lipid digestion. In this study, milk fat globule membrane (MFGM) was used to improve the lipid droplet interface of model infant formula emulsions (IFEs). We focused on the effects of the addition sequence of MFGM and milk proteins commonly used in infant formula (IFE1: Milk proteins added before homogenization, MFGM added after homogenization; IFE2: MFGM added before homogenization, milk proteins added after homogenization; IFE3: MFGM and milk proteins added before homogenization) on lipid droplets' interfacial compositions, structure, and lipid digestion behaviors and compared with human milk (HM) and commercial infant formula (IF). The results showed that the interfacial protein load was significantly lower (P < 0.05), and the interfacial phospholipid load was significantly higher (P < 0.05) in IFE2 compared to IFE1, IFE3, and IF. The lipid droplet structure of IFE2 is closer to that of HM. MFGM fragments-covered lipid droplets can be observed in IFE2. In contrast, the lipid droplets in IFE1, IFE3, and IF were covered by casein micelles, and MFGM fragments were free in the serum phase. After digestion, the lipolysis degree of IFE2 (91.7 ± 1.51%) was comparable to that of HM (94.98 ± 1.08%) and significantly higher than other samples (P < 0.05). During digestion, IFE1 and IFE3 formed thicker and denser protein knit networks compared to IFE2. The lipid droplets in IFE1 and IFE3 were embedded in protein networks, thereby inhibiting lipid digestion. These results indicated that changes in the interfacial composition of lipid droplets improved lipid digestion by mitigating the aggregate and coalescence of protein and lipid droplets.