Total Milk Lipids Research Articles

The identity of the cholesteryl esters in human milk

AbstractMilk samples were collected from 11 mothers who were at least 4 weeks postpartum. The amounts of fat and the fatty acid compositions of cholesteryl esters (CE) and triacylglycerols (TG) in the milk were determined. The mean concentration of total milk lipid was 3.01 gm/100 ml of milk±.42 SD. The major fatty acids esterified with CE and TG were 16∶0,cis 18∶1 and 18∶2. The patterns were similar except for a greater proportion ofcis 18∶1 in the CE. The majortrans fatty acid detected was the 18∶1 isomer which accounted for 4.48% of the TG fatty acids and 2.96% of the CE fatty acids.

Carotene in bovine milk fat globules: observations on origin and high content in tissue mitochondria.

The location and origin of carotenoids in bovine milk fat globules was investigated using spectral absorption of lipid solutions at 461 nm to quantitate carotene. Release of membrane from globules as a result of churning to butter or by freezing and thawing of the globules yielded membrane preparations which were devoid of carotene. Globule cores from these procedures exhibited carotene concentrations comparable to those in total milk lipids. Fractionation of lactating bovine tissue and analysis of lipid extracts revealed that the intracellular fat droplets have carotene concentrations approximating those of secreted globules. However, intracellular membranes of the tissue, particularly the mitochondria, are much richer in carotenoids than formative or secreted fat globules. The evidence indicates that bovine milk fat globules acquire carotene during their formation in the cell, but that some minor fraction of the total carotene may be extracted from the enveloping secretory membrane. Mean carotene values (microgram/g of lipid) for fractions from three samples of lactating tissue were: whole tissue 47, mitochondria 461, microsomes 69, cytosol 67, fat droplets 8, milk 9. One tissue analysis indicated that Golgi membranes contain somewhat more carotene than do microsomes.

Lipid metabolism in the cow during starvation-induced ketosis.

1. Concentrations and compositions of liver, serum and milk lipids of cows were measured during 6 days' starvation and serum lipids during 60 days' re-feeding. 2. The concentration of free fatty acid in serum increased fivefold during starvation. 3. The content of total lipid in liver (g/100g of liver dry matter) doubled owing to a 20-fold increase in triglyceride, an eightfold increase in cholesterol ester, a three fold increase in free fatty acid and a 20% increase in cholesterol. There were no changes in the content or composition of liver phospholipids. 4. Starvation lowered the concentrations of total lipid, phospholipid and cholesterol ester of dextran sulphate-precipitable serum lipoproteins. Total lipid and cholesterol ester concentrations in lipoproteins of d greater than 1.055 and in lipoproteins not precipitable by dextran sulphate decreased from day 4 of the starvation period and during the first 20 days' re-feeding. 5. During starvation there were decreases in percentages of stearic acid and increases in oleic acid in serum free fatty acids and triglycerides and in liver neutral lipid. 6. Throughout starvation total milk lipid yield decreased, yields and percentages of C4-14 fatty acids decreased and percentages of C18 fatty acids increased. 7. It is suggested that accumulation of triglyceride in liver may be caused by increased uptake of plasma free fatty acids without corresponding increase in lipoprotein secretion.

Origin of the milk fat globule.

AbstractMilk fat globules originate as fat droplets within the lactating mammary cell. These droplets are composed largely (>98%) of glycerides. Their constituent fatty acids are derived by lipolysis of very low density lipoproteins and chylomicrons of the blood and by the novo synthesis within the cell. Evidence of two principal routes for the synthesis of milk fat triglycerides has been presented: the so‐called glycerolphosphate and monoglyceride pathways. Recent findings on these pathways are discussed. The nature of the milk triglycerides with their unique compliment and distribution of short chain fatty acids appears to depend upon a closely regulated relation between the soluble multienzyme complex that synthesizes the fatty acids and the glyceride synthetase that is bound to the endoplasmic reticulum. The resulting triglycerides appear to self‐assemble into droplets from the surface of the endoplasmic reticulum. No special ultrastructures (transport particles, vesicles, etc.) have been detected in relation to this process. Milk fat droplets at the time of secretion average several microns in diameter, there being species variations. The basic secretion mechanism involves envelopment of the droplet in plasma membrane and expulsion of it from the cell. As a consequence there are at least two pools of polar lipids (cholesterol and phospholipids) associated with secreted milk fat globules, i.e., one from the plasma membrane and one entrained earlier from the endoplasmic reticulum at the time of triglyceride synthesis and accumulation. In all, the polar lipids do not make up more than 1–2% of the total lipids in milk and a substantial fraction of them has been identified recently with plasma membrane fragments occurring in the skim milk phase. Radiotracer and ultrastructural studies show that this membrane material does not result simply by shedding of surface from milk fat globules. This dispersed material and the lining around milk fat globules constitute valuable sources for the study of cell membranes.

Lipid metabolism. Evidence of a delta-oxidation pathway for saturated fatty acids.

1. Specific radioactivities of milk triglyceride fatty acids and gamma- and delta-hydroxy fatty acids were measured after the intramammary infusion of [1-(14)C]acetate, delta-hydroxy[1-(14)C]laurate and [1-(14)C]laurate as their sodium salts into fed lactating goats. 2. Net incorporations of the radioactive tracer into the total milk lipids were comparable, being 16, 17 and 21% of the label infused respectively. 3. The specific radioactivities of the C(4)-C(8) fatty acids after [1-(14)C]acetate infusion were lower than those of the C(10)-C(14) fatty acids. 4. After delta-hydroxy[1-(14)C]laurate administration the milk triglyceride fatty acids were labelled and their specific radioactivities were characterized by decreasing values with increasing chain length of the fatty acids, implicating C(4) unit incorporation. 5. The gamma- and delta-hydroxy fatty acids isolated after [1-(14)C]laurate infusion were highly labelled and the milk triglyceride fatty acids, other than laurate, exhibited a labelling pattern similar to that of the fatty acids derived from the radioactive delta-hydroxy fatty acid. 6. Evidence is presented for the existence of saturated fatty acid delta-oxidation in the mammary gland, in which the gamma- and delta-hydroxy fatty acids are active intermediates.

Secretion of Radioactivity in Milk Fat after a Single Oral Dose of (3H)Myristic Acid to a Goat.

ABS>Tritium-labeled myristic acid was administered orally as free acid to a lactating goat, and then the secretion of the radioactivity in the total milk lipids and milk glyceride fatty acids was followed for thirteen days. Measurable activity was found in the milk fat 4 hr after administration and the maximum specific activity occurred within 25 hr. About 10% of the radioactivity administered was recovered during the experimental period, and about 25% of the activity collected during 13 days was secreted in the first 28 hr. In the beginning the nonvolatile fatty acids had a higher specific activity than the volatile fatty acids, and there seemed to be a tendency for the specific activities in the short chain acids to increase with time; whereas the long-chain acids appeared to be less active later in the experiment. (auth)