Goat αs1-casein genotype affects milk fat globule physicochemical properties and the composition of the milk fat globule membrane

摘要

Milk fat secretion is a complex process that initiates in the endoplasmic reticulum of the mammary epithelialcell by the budding of lipid droplets. Lipid droplets are finally released as fat globules in milk envelopedby the apical plasma membrane of the mammary epithelial cell. The milk fat globule membrane (MFGM)thus comprises membrane-specific proteins and polar lipids (glycerophospholipids and sphingolipids) surroundinga core of neutral lipids (mainly triacylglycerols and cholesterol esters). We have recently describedmajor proteins of the MFGM in the goat and we have highlighted prominent differences between goats andbovine species, especially regarding lactadherin, a major MFGM protein. Here, we show that, in the goatspecies, the well-documented genetic polymorphism at the αs1-casein (CSN1S1) locus affects both structureand composition of milk fat globules. We first evidenced that both milk fat globule size and ζ-potentialare related to the αs1-casein genotype. At midlactation, goats displaying strong genotypes for αs1-casein (A/Agoats) produce larger fat globules than goats with a null genotype at the CSN1S1 locus (O/O goats). Alinear relationship (R2 = 0.75) between fat content (g/kg) in the milk and diameter of fat globules (μm) wasestablished. Moreover, we found significant differences with regard to MFGM composition (including bothpolar lipids and MFGM proteins) from goats with extremegenotype at the CSN1S1 locus. At midlactation, the amount of polar lipids is significantly higher in theMFGM from goats with null genotypes for αs1-casein (O/O goats; 5.97 ± 0.11 mg/g of fat; mean ± standarddeviation) than in the MFGM from goats with strong genotypes for αs1-casein (A/A goats; 3.96 ± 0.12 mg/gof fat; mean ± standard deviation). Two MFGM-associated proteins, namely lactadherin and stomatin, arealso significantly upregulated in the MFGM from goats with null genotype for αs1-casein at early lactation. Ourfindings are discussed with regard to techno-functional properties and nutritional value of goat milk. In addition,the genetic polymorphism in the goat species appears to be a tool to provide clues to the lipid secretionpathways in the mammary epithelial cell.