Milk mimicry – Triglyceride mixtures that mimic lipid structuring during the digestion of bovine and human milk

It is well recognised that the digestion of milk lipids releases fat-soluble bioactives, primarily in the intestines where 70–90% of lipid digestion occurs. The digestion of milk lipids under intestinal conditions yields fatty acids and monoglycerides that self-assemble into liquid crystalline phases that are species-dependent, suggesting that they play a role in directed nutrition. Yet to date, no studies have proposed mimicking milk liquid crystalline structuring by precisely tailoring the lipids in the digesting emulsions. In this work, the preparation of lipid emulsions that mimic lipid self-assembly in bovine and human milk was examined. Mixtures of between four and eight off-the-shelf homotriglycerides were prepared based on the total fatty acid content of bovine and human milks and these were emulsified using casein. If kept at or above body temperature after emulsification the emulsions were stable and 84 ± 6% (bovine) and 86 ± 3% (human) of the lipids could be digested under intestinal conditions over 2 h. The evolution of liquid crystalline phases was determined as a function of extent of lipid digestion enabled by the well-defined nature of the lipid emulsion and the emulsifying buffer solution. It was found that eight triglycerides with a fine balance of medium- and long-chain triglycerides were required to mimic the bicontinuous cubic phases observed in digesting commercial bovine milk. In contrast, the micellar cubic phases observed in the digestion of donor human milk could be mimicked with simpler lipid mixtures comprising four–seven triglycerides comprising mostly long chain and unsaturated triglycerides. These simplified mixtures are therefore representative colloidal structures that mimic the lipid self-assembly behaviour in digesting dairy emulsions, which can be used as oral delivery vehicles of fat-soluble bioactives targeted towards particular populations including infants in the first year of life.