Structure of bovine milk fat triglycerides

The triglycerides of bovine milk fat globules were isolated and separated into short, medium and long chain lengths by thin-layer chromatography. The molecular weight distribution and the fatty acid composition of the component triglycerides was then separately determined by gas chromatography following argentation-thin-layer and preparative gas chromatography. Some 38 triglyceride types (28% of total), of which there could be up to 6 isomers, were specifically identified and quantitatively estimated. The quantitative estimates for the rest of the milk fat triglycerides were limited to much more complex glyceride groups. The results confirm the earlier claim that butyric and caproic acids occur in milk fat almost exclusively in combination with medium and long chain fatty acids. Presented in part at the AOCS Meeting, Philadelphia, October, 1966.     

Modification of goat milk fat triglycerides by immobilized lipase

The lipid fraction of goat milk was subjected to transesterification using a commercially available immobilized lipase to decrease the amount of short- and medium-chain fatty acids (C₄–C₁₄) by enrichment of the reaction mixture with long-chain (C_18:1 and C_18:2) fatty acids. Aliquots were taken during, transesterification at different reaction times and analyzed for triglycerides and their fatty acid components. The gas chromatographic analyses of triglycerides (previously isolated by thinlayer chromatography) showed that at 6 h reaction under the experimental conditions led to the greatest reduction of the low molecular weight triglycerides (C₂₂–C₃₈) and concomitantly to the greatest increase in the higher molecular weight triglycerides (C₄₈–C₅₄). These changes correlated with the variations observed in the fatty acids of the triglyceride fraction.     

Positional distribution of fatty acids in the triglycerides of bovine milk fat with elevated levels of linoleic acid

A stereospecific distribution of fatty acids in bovine milk fat containing 15.5% linoleic acid has been compared with the distribution in bovine milk fat containing a normal level (1.8%) of linoleic acid. The positional distribution was obtained by the separate analysis of milk fat triglycerides of high, medium, and low molecular weight. The order of preference for linoleic acid in the high molecular weight triglycerides was position 3>position 2 >position 1. There was an accompanying altered distribution of myristic acid and palmitic acid in favor of position 1 at the expense of position 3. However, the proportions of myristic acid and palmitic acid in position 2, relative to positions 1 and 3 were identifical in the high molecular weight fractions of the two milk fats. The distribution of linoleic acid in the medium molecular weight triglycrides of linoleic-rich milk fat was position 1=position 2>position 3. This resulted in a change in the distribution of 18 carbon monounsaturated fatty acids in favor of position 2 at the expense of position 1, but the distribution of myristic acid and palmitic acid was virtually unaltered. The distribution of linoleic acid in the low molecular weight triglycerides was position 2>position 1>position 3. The amounts of myristic acid and palmitic acid in position 2 and of palmitic acid in position 1 decreased in the low molecular weight triglycerides of the milk fat containing elevated levels of linoleic acid. Changes in the distribution of fatty acids which were observed in the separate analysis of the high, medium, and low molecular weight triglycerides were not apparent when comparing the distribution in the total milk fats. For example, the distribution of myristic acid and palmitic acid appeared to be unchanged, while the distribution of 18 carbon monounsaturated fatty acids was slightly altered in favor of positions 2 and 3. Moreover, linoleic acid showed an almost equal preference for the three positions of the glycerol moiety in milk fat containing elevated levels of this fatty acid with some concentration at position 2.     

Intramolecular fatty acid distribution in milk fat triglycerides of monkeys

Pancreatic lipase hydrolysis was used to determine the distribution of fatty acids in the milk triglycerides of four species of monkeys and of human milk. The patterns of the major fatty acids were generally similar in all species examined, but there were some differences in the relative concentrations of individual fatty acids esterified at either the 2 or 1,3 positions. Caprylic, stearic, oleic, and linoleic acids were found predominantly at the 1,3 positions; in contrast, lauric, myristic, palmitic, and palmitoleic were concentrated at the 2 position. Monkey milk fats had greater proportions of these acids at the respective positions than did bovine milk fat. Also, the monkey fats were relatively uniform both in total unsaturated fatty acids (41–48%) and in the proportion of these esterified at the 2 position (19–26%). In general, both the fatty acid composition and the specific distribution of fatty acids in the monkey milk fats more closely resembled the patterns in human milk fat than did those in ruminant milk fats.     

Analysis of triglycerides by consecutive chromatographic techniques. II. Ucuhuba kernel fat

The triglycerides from ucuhuba kernel fat (Virola surinamensis) were analyzed using thinlayer adsorption chromatography (TLC) followed by gas-liquid chromatography (GLC). The triglycerides were first separated into three fractions containing 0, 1, and 2 or more double bonds per molecule on silica gel TLC plates impregnated with AgNO₃. The total triglycerides and each individual TLC fraction were then analyzed by GLC for the molecular weights of their component triglycerides and for their fatty acid composition. Quantitation of the TLC fractions was achieved by GLC analysis of their fatty acids using an added internal standard and confirmed by solving simultaneous equations derived from GLC analysis of their triglycerides and fatty acids. Application of these combined chromatographic techniques separated the ucuhuba kernel fat into 23 triglyceride components. Trimyristin and laurodimyristin comprised over half the total triglycerides, which was expected since the fat contained 20.0 mole % laurie and 71.3% myristic acids. Presented at the AOCS Meeting in Houston, Texas, 1965. Supported in part by grants from the National Institutes of Health (AM-06011) and the Corn Products Institute of Nutrition.     

Polymorphism of saturated triglycerides: II. 1,3-dipalmito triglycerides

Differential scanning calorimetry was used to examine triglycerides of the 16-N-16 series, whereN is an even-carbon, saturated fatty acid of 2 to 18 carbons in length. The procedures used to obtain heats of fusion and crystallization of the various triglycerides and their polymorphs are described. Small samples (ca. 1-2 mg) were used to investigate polymorphs with relatively rapid rats of conversion, but more accurate calorimetric data were obtained with larger samples. Capillary melting points were also obtained for the various triglycerides and their polymorphs. Calorimetric and melting point data are given.     

Structure of the human milk fat globule

Milk is a sophisticated oil‐in‐water emulsion in which triacylglycerols, the single largest component of the infant's energy supply, are enclosed by an unusual trimolecular layer of polar lipids, proteins and cholesterol. Recently, interest has turned to the possibility that not just the membrane components and triacylglycerol fatty acids, but also their unusual structures may be particular features that enable delivery of intact bioactive molecules to the intestine, while facilitating efficient absorption and processing of milk fats, without metabolic stress. These features mean that the functional properties of milk fats are not replicated by mixtures of vegetable oils and emulsifiers and may be lost by processing. However, they offer opportunities for use of milk fat globule membranes and triacylglycerols structured to resemble milk fats.     

Specific distribution of fatty acids in the milk fat triglycerides of goat and sheep

The triglycerides of the fat globules of sheep and goat milk were isolated and separated into short and long chain lengths by silicic acid column chromatography. The short chain lengths comprised major triglycerides with 34–44 acyl carbon atoms and accounted for nearly 50% of the total milk fat. The long chain lengths contained major triglycerides with 40–54 acyl carbons. Stereospecific analyses of the short chain triglyceride fraction showed that of the 20–23 moles per cent of C₄−C₈ fatty acids present, at least 95% were specifically attached to the glycerol molecule in the position corresponding to carbon 3 ofsn-glycerol. The distribution of the other fatty acids (C₁₀ or greater) did not show such marked specificity for either the 1 or the 2 position. Although individual triglycerides were not identified, the specific placement of the fatty acids could best the accounted for by assuming a common pool of long chain 1,2-diglycerides which served as precursors of the bulk of both short and long chain triglycerides during milk fat synthesis. Presented in part at the AOCS Meeting, New York, October 1968.     

Determination of milk fat in chocolates by gas-liquid chromatography of triglycerides and fatty acids

The combination of two routine methods is proposed to determine the content of milk fat (MF) in chocolates, which is applicable even in the presence of lauric fats or others. The content of MF is obtained from the sum of C₄₀, C₄₂, and C₄₄ medium-chain triglycerides, determined by capillary gas-liquid chromatography (GLC). A new method, based on methyl esters of lauric acid and on minor acids situated between myristic and palmitic, is proposed. It enables detection and estimation of potential lauric fats, as well as the determination of the actual content of MF. The influence of other vegetable and animal fats is discussed. We analyzed 45 MF samples extracted from industrial milk powders and from pure or fractionated MF for chocolate manufacturing or pastry by GLC of triglycerides. We also analyzed by capillary GLC the methyl esters from 22 of those fats. Mixtures of these 22 MF samples with a cocoa butter also were used for chromatographic analyses of methyl esters and triglyceride. Results from the various analytical methods have been presented.     

Long and medium chain triglycerides increase plasma concentrations of ketone bodies in suckling rats

The potential of medium chain triglyceride (MCT) and long chain triglyceride (LCT) as sources of plasma ketones was investigated in suckling rats. Initially high concentrations of plasma ketones in 6-, 10-, and 17-day-old rats increased 2- to 3-fold after acute feeding of MCT. This feeding had the same effect in fed or fasted adult rats. Corn oil (as a source of LCT) induced a large increase in the plasma ketone concentration of suckling rats and a relatively small but significant increase in fasted adult rats. The LCT treatment did not affect plasma ketone levels in fed adult rats. The results show clearly that feeding either LCT or MCT will enhance hyperketonemia in suckling rats. In the livers of all animals, regardless of age, the capacity for incorporation of [1-¹⁴C] octanoate into CO₂ and acetoacetate far exceeded that for [1-¹⁴C] palmitate. The hyperketonemic action of LCT in suckling rats was accompanied by an increased activity of carnitine palmityltransferase and increased level of carnitine.     

Mass spectrometry of triglycerides: II. Specifically deuterated triglycerides and elucidation of fragmentation mechanisms

Deuterium labeled monoacid triglycerides were synthesized and their mass spectra were measured. The spectra provided further support for proposed (1) structures of principal ions, knowledge about the formation of [M-18]⁺, the interexchange of hydrogen atoms between 2 and the 5,6 or 7 positions and the explusion of part of the alkyl chain. Presented in part at the AOCS Meeting, New Orleans, April 1970. Part VI of a series on Mass Spectrometry of Lipids. For V see Lipids 5:861–868 (1970).     

Triglyceride composition of bovine milk fat with elevated levels of linoleic acid

The effect of increasing the linoleic acid (18∶2) content of milk fat on the composition and structure of the triglycerides (TG) was investigated. Protected sunflower seed supplement was added to the diet of a cow grazing on pasture, and the structure and composition of the milk fat compared with the milk fat from its monozygous twin which had been fed a control diet. The relative proportions of TG fractions of high, medium, and low molecular weight in the milk fat with elevated levels of 18∶2 (15.5% 18∶2) were 43.0, 19.5, and 37.5 moles %, respectively, compared with 36.1, 19.7, and 44.2 moles %, respectively, in the milk fat from the cow fed the control diet. Separation of these three TG fractions of each milk fat into TG classes with different levels of unsaturation showed that the milk fat with elevated levels of 18∶2 contained higher proportions of diene, triene, and tetraene TG and correspondingly lower proportions of saturated and, to a lesser extent, monoene TG. The saturated and monoene TG from the two milk fats had similar fatty acid compositions. However, the diene TG of the 18∶2-rich milk fat included high proportions of the combination of 18∶2 with two saturated fatty acids (FA) which are minor constituents of normal milk fats. Likewise, the triene TG reflected the presence of 18∶2 in combination with 18∶1 and a saturated FA.     

The structural components of milk triglycerides

Pancreatic lipase hydrolysis and gas chromatographic analysis of two samples of butter fat show that the individual acyl groups are not dispersed at random among all the glyceryl carbons. When considered only as saturated or unsaturated, and not as individuals, they appear to be distributed intermolecularly at random, or nearly so, but tend to assume specific positions intramolecularly. Presented at the 51st annual meeting, American Oil Chemists’ Society, Dallas, Tex., April 4–6, 1960.     

Determination of the conjugated linoleic acid-containing triacylglycerols in New Zealand bovine milk fat

Reversed-phase high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection at 233 nm was used to separate, quantify, and identify the triacylglycerols (TAG) of milk fat that contain conjugated linoleic acid (CLA). The absorbance at 233 nm was substantially due to CLA-TAG (chromatography of some representative TAG devoid of CLA, such as tripalmitin and triolein, showed poor responses at 233 nm, 1/800th that of CLA-TAG). A CLA molar extinction coefficient at 233 nm of 23 360 L mol⁻¹ cm⁻¹ and an HPLC UV response factor were obtained from a commercially available cis-9, trans-11-CLA standard. This molar extinction coefficient was only 86% reported literature values. Summation of all chromatographic peaks absorbing at 233 nm using the corrected response factor gave good agreement with independent determinations of total CLA by gas chromatography and UV spectrophotometry. This agreement allowed quantification of individual CLA-TAG peaks in the HPLC separation of a typical New Zealand bovine milk fat. Three CLA-containing TAG, CLA-dipalmitin, CLA-oleoyl-palmitin and CLA-diolein, were prepared by interesterification of tripalmitin with the respective fatty acid methyl esters and used to assign individual peaks in the reversed-phase chromatography of total milk fat, of which CLA-oleoyl-palmitin was coincident with the largest UV peak. Band fractions from argentation thin-layer chromatography of total milk fat were similarly employed to identify five predominant CLA-TAG groups in total milk fat: CLA-disaturates, CLA-oleoyl-saturates, CLA-vaccenyl-saturates, CLA-vaccenyl-olein, and CLA-diolein.     

Animal endogenous triglycerides: II. Rat and chicken adipose tissue

The endogenous adipose tissue triglycerides of rat and chicken differ markedly in composition from those of swine although all three contain the same major fatty acids. The main difference is that the swine triglycerides have saturated fatty acids in the middle position, whereas in rat and chicken that position is preferentially occupied by unsaturated acids. In swine adipose tissue triglycerides the order of preference for the middle position is 16∶0>16∶1>18∶0>18∶1, whereas in rat and chicken triglycerides the order is 18∶1>16∶1>18∶0>16∶0. Generalizing, in swine the order of preference for the 2 position is chain length over unsaturation, shorter chains over longer chains, and saturation over unsaturation. In rat and chicken, the degree of unsaturation prevails over chain length, longer chains over shorter chains, and unsaturation over saturation.     

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 blobules. 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 (μg/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.     

Regiospecific analysis of fractions of bovine milk fat triacylglycerols with the same partition number

Bovine milk fat was fractionated using preparative reversed-phase high-performance liquid chromatography. The conditions consisted of two successive linear gradients of acetonitrile and tert-butylmethylether, followed by a final isocratic mixture of the two eluants, leading to triacylglycerols grouped by their partition number (PN). Fractions corresponding to partition numbers 32 to 50 were isolated and analyzed for fatty acid distribution between sn-1,3 and sn-2 positions by Grignard degradation. Results showed that the fatty acid distribution in milk fat triacylglycerols is nonrandom. The distribution of short-chain fatty acids, stearic (predominantly at sn-1,3 position) and palmitic (predominantly sn-2 position), did not change with triacylglycerol size. Medium-chain fatty acids were predominantly located at sn-2 position, but their proportion at this position decreased with triacylglycerol size. Oleic acid distribution was also size-dependent in that it was located in high proportions at sn-2 position in smaller triacylglycerols and vice versa. Results also showed that the sn-2 position was more unsaturated than sn-1,3 position in the PN range from 32 to 40, but it was more saturated in triacylglycerols with higher PN.     

Long chain alkanesulfonates and 1-hydroxy-2-alkanesulfonates: Structure and property relations

Even chain sodium alkanesulfonates from the Strecker reaction, odd chain sodium alkanesulfonates from the alkaline decarboxylation of α-sulfo acids, and sodium 1-hydroxy-2-alkanesulfonates from the reduction of esters of α-sulfo acids were compared with respect to Krafft point, critical micelle concentration, detergency and foam height. Sodium alkanesulfonates and crude fusion products from the α-sulfo acids (mixtures of alkanesulfonates of one less carbon atom with a lesser amount of a soap of two less carbon atoms) are more soluble and have better detergent and foaming properties. Sodium 1-hydroxy-2-alkanesulfonates resemble monosodium salts of α-sulfo acids. Alkanesulfonic acids and 1-hydroxy-2-alkane-sulfonic acids obtained from the sodium salts by ion exchange have lower Krafft points and are more readily soluble. The critical micelle concentrations of 1-hydroxy-2-alkanesulfonic acids and α-sulfo acids are nearly the same and about equal to those of alkanesulfonic acids of one less carbon atom. Presented at the AOCS meeting in Toronto, Canada, 1962. A laboratory of the E. Utiliz. Res. & Dev. Div., ARS, U.S.D.A.     

Analysis of triglycerides by consecutive chromatographic techniques. i.cuphea llavia seed fat

The triglycerides ofCuphea llavia var.miniata seed fat were separated according to the number of double bonds/molecule using preparative thin layer chromatography (TLC) on silicic acid impregnated with silver ion. The recovered frac-tions were quantitated by the chromotropic acid technique. Each fraction was then separated ac-cording to mol wt using gas-liquid chromatog-raphy (GLC). This multiple chromatography procedure resolvedC. llavia triglycerides into 17 different components. The triglyceride composition ofC. llavia seed fat was calculated from the above results. Since the fat contains 91.2 mole % decanoic acid, it was expected that each triglyceride molecule would contain at least two molecules of decanoic acid. Results showed this to be generally true, but sev-eral minor component triglycerides not conform-ing to this pattern were found. Presented at the AOCS Meeting in Minneapolis, 1963.     

Influence of elevated levels of linoleic acid on the thermal properties of bovine milk fat

The thermal properties of bovine milk fat containing 15.5% linoleic acid have been compared with those of milk fat containing a normal level (1.8%) of linoleic acid in order to examine the influence of altered triglyceride (TG) composition on their physical characteristics. The total TGs of 18∶2-rich milk fat melted over the range −38 to 30 C compared with the range −33 to 34 C for control milk fat. Polymorphism exhibited by the high mol wt TGs of control milk fat was absent in the same fraction of 18∶2-rich milk fat. Similarly, the complex melting thermogram of the low mol wt TGs of control milk fat and its obvious polymorphic behavior contrasted with the single broad melting peak of the low mol wt TGs of 18∶2-rich milk fat. This solid miscibility in the 18∶2-rich milk fat could be a consequence of the lower proportion of saturated TGs or the presence of high proportions of diene and triene TGs containing 18∶2 instead of monoene and diene TGs containing 18∶1.