Bovine Milk-Derived Emulsifiers Increase Triglyceride Absorption in Newborn Formula-Fed Pigs

Abstract

Efficient lipid digestion in formula-fed infants is required to ensure the availability of fatty acids for normal organ development. Previous studies suggest that the efficiency of lipid digestion may depend on whether lipids are emulsified with soy lecithin or fractions derived from bovine milk. This study, therefore, aimed to determine whether emulsification with bovine milk-derived emulsifiers or soy lecithin (SL) influenced lipid digestion in vitro and in vivo. Lipid digestibility was determined in vitro in oil-in-water emulsions using four different milk-derived emulsifiers or SL, and the ultrastructural appearance of the emulsions was assessed using electron microscopy. Subsequently, selected emulsions were added to a base diet and fed to preterm neonatal piglets. Initially, preterm pigs equipped with an ileostomy were fed experimental formulas for seven days and stoma output was collected quantitatively. Next, lipid absorption kinetics was studied in preterm pigs given pure emulsions. Finally, complete formulas with different emulsions were fed for four days, and the post-bolus plasma triglyceride level was determined. Milk-derived emulsifiers (containing protein and phospholipids from milk fat globule membranes and extracellular vesicles) showed increased effects on fat digestion compared to SL in an in vitro digestion model. Further, milk-derived emulsifiers significantly increased the digestion of triglyceride in the preterm piglet model compared with SL. Ultra-structural images indicated a more regular and smooth surface of fat droplets emulsified with milk-derived emulsifiers relative to SL. We conclude that, relative to SL, milk-derived emulsifiers lead to a different surface ultrastructure on the lipid droplets, and increase lipid digestion.

Keywords: absorption; emulsions; fat; gastric lipase; intestine; milk; preterm neonates; soy lecithin; vegetable oil.

Figure 1

Titration of free fatty acids during simulated human gastric digestion with recombinant human gastric lipase (rHGL) and pepsin at pH 6.4 (0–50 min) and pH 6.5 (50–140 min) of 3.5% oil-in-water emulsions using either whey protein concentrate from acid whey-enriched in extracellular vesicles (WPC-A-EV) (n = 3), WPC enriched in phospholipids (WPC-PL) (n = 3), whey protein concentrate from acid whey enriched in triglycerides (WPC-A-TAG) (n = 3), whey protein concentrate from acid whey enriched in soluble whey protein (WPC-A-WP) (n = 3), and soy lecithin (SL) (n = 2 due to removal of outliers). Values are presented as mean ± SD. ** p < 0.001. *** p < 0.0001.

Figure 2

Particle size distribution and transmission electron microscopy (Panel 1): Volume mean diameter for each of the 3.5% oil-in-water emulsions, WPC-A-EV, WPC-PL, WPC-A-TAG, WPC-A-WP, and soy lecithin (SL). n = 3. Values are presented as means ± SD. (Panel 2): Micrographs from transmission electron microscopy (subpanels A, B, C) and cryo-scanning electron microscopy (subpanels D, E, F) of three emulsions. A and D: WPC-PL emulsion, B and E: WPC-A-EV emulsion, C and F: SL emulsion. The scale bar for micrographs A–C is 500 nm, and D–F is 2 µm. The arrow in A points out the dark layer, in E the arrow points out the lipid droplet’s smooth surface, and in F the arrow points out the thick and uneven surface of the lipid droplet.

Figure 3

Total fecal stoma output (upper panel), total fat output in the feces (middle panel) and fat absorption percentages (lower panel) on day 3, 4, and 7 (WPC-PL n = 6–9, SL n = 5–9). Values presented as mean ± SD.

Figure 4

Triglyceride levels in plasma, mmol/L, as pooled data across day two and three in upper panel (WPC-PL n = 16, SL n = 18), and data from day two in middle panel (WPC-PL n = 9, SL = 9) and three in lower panel (WPC-PL n = 9, SL n = 7) separately. Values presented as means ± SD.

Figure 5

Triglyceride levels in plasma at day two (WPC-A-EV n = 16, WPC-PL n = 16, SL n = 17) and four (WPC-A-EV n = 15, WPC-PL n = 14, SL n = 17), baseline sample and 30, 60, 90 and 120 min after a test bolus was given. Presented as mean ± SD. * p < 0.01. ** p < 0.001.

Figure 6

(Top panel): Gastric pH for WPC-A-EV (n = 14), WPC-PL (n = 11), and SL (n = 17) in gastric content collected post euthanasia. (Bottom panel): Gastric lipase activity for WPC-A-EV (n = 13), WPC-PL (n = 11), and SL (n = 16) in gastric content collected post euthanasia. ** p < 0.01.