Abstract
During secretion of milk fat globules, triacylglycerol (TAG) droplets are enveloped by a phospholipid (PL) trilayer. Globule size has been found to be related to polar lipid composition and fat content, and milk fat content and fatty acid composition have been associated with the diacylglycerol acyltransferase 1 (DGAT1) K232A polymorphism; however, the association between the DGAT1 polymorphism and fat globule size and polar lipid composition has not been studied. The ratio between polar and neutral lipids as well as the composition of the polar lipids in milk has industrial as well as nutritional and health implications. Understanding phenotypic and genotypic factors influencing these parameters could contribute to improving milk lipid composition for dairy products. The focus of the present study was to determine the effect of both fat content and DGAT1 polymorphism on PL/TAG ratio, as a marker for milk fat globule size, and detailed PL composition. Milk samples were selected from 200 cows such that there were equal numbers of samples for the different fat contents as well as per DGAT1 genotype. Samples were analyzed for neutral and polar lipid concentration and composition. PL/TAG ratio was significantly associated with both fat content and DGAT1 genotype. Phosphatidylinositol and phosphatidylserine concentrations were associated with fat content*DGAT1 genotype with a stronger association for the AA than the KK genotype. Sphingomyelin concentration tended to interact with fat content*DGAT1 genotype. Phosphatidylethanolamine (PE) concentration showed a biphasic response to fat content, suggesting that multiple biological processes influence its concentration. These results provide a new direction for controlling polar lipid concentration and composition in milk through selective breeding of cows.
Highlights
Dietary fat has been the focus of many health-related studies due to the connection between its consumption and health conditions such as obesity, diabetes and atherosclerosis
Compelling evidence has been provided for the effect of the K232A polymorphism of the diacylglycerol acyltransferase 1 (DGAT1) gene on bovine milk fat content [16] and fatty acid composition [17]
The main finding of our study is that DGAT1 polymorphism plays a significant role in milk fat macrostructure as reflected by PL/TAG ratio
Summary
Dietary fat has been the focus of many health-related studies due to the connection between its consumption and health conditions such as obesity, diabetes and atherosclerosis. An increasing body of evidence indicates that it is the fat content of the diet and its composition that should be considered, because of the difference in metabolic and health impact of different fatty acids and lipid species [1,2,3]. Fatty acids in the diet are almost never consumed as free fatty acids. Rather, they are present in foods as part of larger lipid molecules, primarily triacylglycerols (TAG) and, to much lesser extent, as polar lipids, glycerophospholipids and sphingolipids (i.e. phospholipids, PL). Understanding the mechanisms determining the ratio between PL and TAG in food is of great importance
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