Effect of lipid droplet size on the digestion of goat milk proteins with different casein:whey protein ratios

Lipids as main energy source in infant formula may influence the digestion of proteins. This study aimed to determine the effects of lipid addition and droplet size on the digestion of goat milk proteins in two infant formula model systems. For these systems, skimmed goat milk was diluted to 12 g/L protein with 80% casein and 20% whey proteins (C80 sample), for the C40 sample (40% casein and 60% whey protein) whey protein concentrate was added. A vegetable oil blend at 3.12 g/L was incorporated into these samples, which were then processed to achieve either large lipid droplets (approximately 800 nm) or small lipid droplets (approximately 200 nm). A simulated infant digestion model was used to evaluate the impact of lipid presence and droplet size on the digestion of proteins. The reduced protein digestibility in samples with lipids may be attributed to proteins covering the lipid droplet surface, decreasing accessibility for enzymes. Compared to the samples with large lipid droplets, the samples with small lipid droplets have more droplet surface area binding proteins, which may explain the lower soluble protein content and protein digestibility, leading to more undigested proteins. C80 samples showed higher digestibility than C40 samples both with and without lipid. Lipid droplets coalesced during digestion, particularly with higher casein content. Both caseins and whey proteins combined with lipid droplets were entrapped in the floating coagulum during the digestion. To achieve a higher protein digestibility, C80 samples with larger lipid droplet would be recommended. These findings provide valuable insights for optimizing infant formula compositions to enhance protein digestibility and overall nutritional efficacy.