A Review of the Metabolic Origins of Milk Fatty Acids

Abstract

Milk fat and its fatty acid profile are important determinants of the technological, sensorial, and nutritional properties of milk and dairy products. The two major processes contributing to the presence of fatty acids in ruminant milk are the mammary lipogenesis and the lipid metabolism in the rumen. Among fatty acids, 4:0 to 12:0, almost all 14:0 and about a half of 16:0 in milk fat derive from de novo synthesis within the mammary gland. De novo synthesis utilizes as precursors acetate and butyrate produced through carbohydrates ruminal fermentation and involves acetyl-CoA carboxylase and fatty acid synthetase as key enzymes. The rest of 16:0 and all of the longchain fatty acids derive from mammary uptake of circulating lipoproteins and nonesterified fatty acids that originate from digestive absorption of lipids and body fat mobilization. Further, long-chain fatty acids as well as medium-chain fatty acids entering the mammary gland can be desaturated via Δ-9 desaturase, an enzyme that acts by adding a cis-9-double bond on the fatty acid chain. Moreover, ruminal biohydrogenation of dietary unsaturated fatty acids results in the formation of numerous fatty acids available for incorporation into milk fat. Ruminal biohydrogenation is performed by rumen microbial population as a means of protection against the toxic effects of polyunsaturated fatty acids. Within the rumen microorganisms, bacteria are principally responsible for ruminal biohydrogenation when compared to protozoa and anaerobic fungi.

Dietary sesame seed hulls utilization on lamb performance, lipid oxidation and fatty acids composition of the meat

“…Research has shown that ruminant meat fatty acid profile can be influenced by different rations [34], such as the inclusion of rich PUFA sources in cattle diets [35]. Dietary lipids are subjected to lipolysis by rumen bacteria, which then hydrogenate and isomerize the PUFA included in the feed to more saturated end products [36,37]. At the same time metabolites such as rumenic acid (9 cis, 11 trans-18:2) or vaccenic acid (11 trans-18:1) are produced, which are consider to be beneficial for the consumer [38].…”

“…Accordingly, the most common fatty acids, as well as SFA, MUFA, and PUFA did not differ significantly (P>0.050) between the three experiments groups, in contrast with the original hypothesis of the experiment. It is possible that since SSH unsaturated fatty acids are not protected, they are quickly saturated in the rumen, before being absorbed along the small intestine of the animal [36,37,40].…”

Effect of supplementation of inulin in dietary on lactation performance, rumen fermentation, ruminal microbial profile and metabolites in dairy cows

“…On the other hand, the results of metabolomics in our study revealed that the supplementation of inulin signi cantly downregulated the lipid metabolism in dairy cows. The increase in the ratio of SFA leaded to a decrease in the ratio of UFA [25]. The decrease in C18:1 trans-9 and C18:2 cis-6 might be related to the hydrogenation of rumen microorganisms, which could reduce the toxicity of UFA [26].…”

“…were decreased. The increase in SMCFA might due to the increase in the concentration of acetate and butyrate in the rumen, which are the substrates for de novo synthesis of milk FA by mammary epithelial cells [25], while about half of the C16:0 and other long-chain FA in milk fat are directly absorbed from blood lipids [25]. On the other hand, the results of metabolomics in our study revealed that the supplementation of inulin signi cantly downregulated the lipid metabolism in dairy cows.…”

The effect of long term under- and over-feeding on the expression of genes related to lipid metabolism in the mammary tissue of goats

“…40%) and the uptake from circulation of preformed FA in blood (ca. 60%) (Cozma et al, 2013). More specifically, MT: synthesize short-and medium-chain FA using acetate and 3-hydroxybutyrate in the present of two key enzymes, acetyl-Co A carboxylase (ACACA) and fatty acid synthatase (FASN), and uptake FA from the plasma with the involvement of lipoprotein lipase (LPL) (Harvatine et al, 2009;Shingfield et al, 2010).…”