FRET/SAXS integration reveals the digestion-absorption trade-off driven by dynamic self-assembly of human milk triacylglycerols.

This study integrates fluorescence resonance energy transfer (FRET) and small-angle X-ray scattering (SAXS) to elucidate, in real time, how triacylglycerol (TAG) self-assembly dynamics in human milk regulate digestion and absorption. Among three major human milk TAGs-1-oleoyl-2-palmitoyl-3-linoleoyl-glycerol (OPL), 1,3-dioleoyl-2-palmitoyl-glycerol (OPO), and 1,3-dilinoleoyl-2-palmitoyl-glycerol (LPL)-OPL showed ∼20% faster lipolysis and more rapid micelle formation (IRhB/IFITC stabilized 60 min earlier, RSD < 5%), likely due to its asymmetric sn-1,3 acyl chain structure. However, OPL-assembled micelles had ∼25% lower molecular packing density (qmax) and ∼ 20% lower interfacial stability (KPorod) than OPO/LPL. This "fast-assembly-loose-structure" profile led to ∼10% slower diffusion of OPL digestion products in mucus, suggesting that although OPL digests efficiently, its absorption is hindered by unstable self-assemblies that disintegrate in mucus. These findings reveal a previously unrecognized antagonism between digestion and absorption driven by lipid molecular structure, providing new insights into the design of lipid ingredients in infant formula.