Abstract
Lipids in milk are secreted as a triacylglycerol core surrounded by a trilayer membrane, the milk fat globule membrane (MFGM). This membrane, known to have important roles in infant brain and intestinal development, is composed of proteins, glycoproteins, and complex lipids. We hypothesized that some of the beneficial properties of MFGM are due to its effects on the gastrointestinal microbiota. This study aimed to determine the effect of a commercial phospholipid concentrate (PC) and enriched bovine, caprine, and ovine MFGM fractions on ileal and hindgut microbiota in vitro. Digestion of PC and MFGMs was conducted using an in vitro model based on infant gastric and small intestine conditions. The recovered material was then in vitro fermented with ileal and caecal inocula prepared from five piglets fed a commercial formula for 20 days before ileal and caecal digesta were collected. After each fermentation, samples were collected to determine organic acid production and microbiota composition using 16S rRNA sequencing. All substrates, except PC (5%), were primarily fermented by the ileal microbiota (8–14%) (P < 0.05). PC and caprine MFGM reduced ileal microbiota alpha diversity compared to ileal inoculum. Caprine MFGM increased and PC reduced the ileal ratio of firmicutes:proteobacteria (P < 0.05), respectively, compared to the ileal inoculum. Bovine and ovine MFGMs increased ileal production of acetic, butyric, and caproic acids compared to other substrates and reduced the proportions of ileal proteobacteria (P < 0.0001). There was a limited fermentation of bovine (3%), caprine (2%), and ovine (2%) MFGMs by the caecal microbiota compared to PC (14%). In general, PC and all MFGMs had a reduced effect on caecal microbiota at a phylum level although MFG source-specific effects were observed at the genus level. These indicate that the main effects of the MFGM in the intestinal microbial population appears to occur in the ileum.
Highlights
Milk fat is secreted from the mammary gland in the form of milk fat globules (MFG) composed of a triacylglycerol core covered by a trilayer membrane, the milk fat globule membrane (MFGM)
The enrichment method increased the concentration of proteins putatively identified in Figure 2 as part of the MFGM [mucin 1 (250–450 kDa), xanthine oxidase, PAS III, CD36, butyrophilin, adipophilin and/or lactadherin (PAS 6/7; 52–58 kDa bovine, 55 kDa caprine), compared to bovine, caprine, and ovine lanes 6 and 7)] milk
The enriched MFGM fraction obtained in this study contained proteins and polar lipids characteristic of the native MFGM as previously reported for bovine [44], caprine [36], and ovine milk [16]
Summary
Milk fat is secreted from the mammary gland in the form of milk fat globules (MFG) composed of a triacylglycerol core covered by a trilayer membrane, the milk fat globule membrane (MFGM). MFG are digested and absorbed in different areas of the intestinal tract, which affects the nutritional and functional role of the MFGM components. Indicate that specific components of the bovine MFGM, such as glycoproteins, could reach the large intestine [10]. The infant’s gastrointestinal tract is immature with suboptimal pH for digestive enzymes and lower concentrations of bile acids and enzymes [13, 14]. This could reduce the digestion of MFGM components in the stomach and small intestine and, increase the amount of undigested MFGM reaching the large intestine
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