HPLC of triglycerides

Triglyceride separation was investigated on a reverse phase high performance liquid chromatography (HPLC) column using two different solvent systems. Complete separation of model compounds differing by two methylene groups was achieved. Partial or complete separation was also observed in critical pairs; for example, the different types of triglycerides consisting of palmitic and oleic acids. This observation was confirmed on natural oils (coconut oil, palm kernel oil).     

Methanolysis of triglycerides

Summary Alkali-catalyzed methanolysis of fats as a means of preparing methyl esters for analytical purposes has been investigated. Of the various catalysts employed sodium methoxide and ignited potassium carbonate have been found to set free 99–99.5% of total glycerol and to cause the least degree of saponification.     

Polymorphism of saturated triglycerides: I. 1,3-distearo triglycerides

Triglycerides of the 18-N-18 series, whereN is an even-carbon saturated fatty acid of 2 to 18 carbons in length, were examined by differential scanning calorimetry. The procedures used to obtain heats of fusion and crystallization of the various triglycerides and their polymorphs are described. When small samples (ca. 1–2 mg) were used, the temperature lag was minor at rapid scanning rates thus permitting investigation of polymorphs with relatively rapid rates 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 were given.     

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.     

Thermal oxidation of synthetic triglycerides I. composition of oxidized triglycerides

Tripalmitin, 1- and 2-lauryl dipalmitin and 1- and 2-oleyl dipalmitin were subjected to thermal oxidation at 200C in the presence of air for various lengths of time. The triglycerides showed a loss in weight, and an increase in carbonyl hydroxyl and acid values. The I.V. increased in the case of saturated triglycerides and decreased in the case of unsaturated triglycerides. Hydrolysis of the ester linkage between glycerol and fatty acid was found to occur during thermal oxidation of the type and position of the fatty acid in the triglyceride molecule. The fatty acids released from the triglyceride by hydrolysis were found either to be oxidized further to short chain fatty acids, or were oxygenated with the introduction of a carbonyl or hydroxyl group in the molecule. Moreover, the unsaturated fatty acid in the triglyceride molecule was found to be oxidized more readily than the saturated fatty acid. A hydroxy fatty acid with a carbon number of 13.5 on a diethylene glycol succinate column was isolated from oxidized tripalmitin and was also found to occur in the free fatty acid fraction of oxidized tripalmitin, 1-lauryl, 2–3 dipalmitin, and 1-oleyl, 2–3 dipalmitin. The presence of laurie or oleic acid in the 2-position of the triglyceride prevented the formation of this acid, which suggested that it is an oxidation product of palmitic acid. Portion of a thesis presented by J. G. Endres as partial fulfillment of the requirements for the degree of Ph.D. in food technology. Funds for partial support of these studies were made available by the National Institute of Health, Grant A-1671.     

Suspensions of high-melting triglycerides

A method for preparing stable oil/water suspensions of cottonseed stearine, tristearin, tripalmitin, trimyristin, methyl stearate, and palmitic acid in concentrations up to 10% with minimum concentrations of stabilizing agents is described. Using 2.5% of polyethylene glycol 400 monostearate (based on weight of hard fat), 0.1% of Pluronic F 68, and 0.2–0.25% of Carbopol 934 (the concentrations of these two agents are based on the weight of the aqueous phase), suspensions of the hard fats were prepared by simple stirring, were stable for at least one month at room temperature, and could be sterilized. The size of the dispersed fat particles was 20–40 μ. Apparent viscosities of cottonseed stearine suspensions at 2, 5, and 10% concentrations were 3.59, 5.95, and 6.62 poises at 25C, respectively. Suspensions as described should have utility in those areas of investigation in which solid fatty materials in the form of stable dispersions are desirable. Presented at the AOCS meeting in New Orleans, La., 1962. This work was supported by funds of the Office of the Surgeon General, U. S. Army, Washington, D. C. A laboratory of the So. Utiliz. Res. & Dev. Div., ARS, U.S.D.A.     

Interesterification reactions of triglycerides

Summary A study of the interesterification reaction has been undertaken using synthetic triglyceride systems (triolein in varying proportions with tripalmitin) and also combinations of lard and hydrogenated lard. An empirical crystallization method has been used in determining the amount of trisaturated glycerides present in a mixed fat. The results indicate that the end-products of interesterification approach the composition expected from the principle of random distribution. Presented before the fall meeting of the American Oil Chemists’ Society, Nov. 7–9, 1945, in Chicago.     

Radical chlorinations of triglycerides

Several triglycerides were synthesized with an iodoaroyl group. Intramolecular radical chain transfer chlorinations were conducted that resulted in the associated pair of fatty acids of the triglyceride becoming chlorinated. The distribution of monochlorinated species was similar to that obtained by direct radical chlorination of the relevant fatty acid methyl esters. Functionalization was, as expected, away from the carboxylate group but gave no indication that either alignment of chains or the constraints of an intramolecular process could limit the manifold of products of the reaction. To gauge the effect on halogenation of a structure, bearing more than one electron-withdrawing group, methyl oleate was converted to thebis trifluoroacetate of methyl 9,10-dihydroxystearate. No products of chlorination on carbons 2–8 were observed.     

Stereospecific analysis of triglycerides

Stereospecific analysis determines how the fatty acids of triglycerides are distributed over the three different positions of the glycerol. The special problem is the differentiation of position I-1 and L-3 of glycerol. In the presently known methods, triglycerides are first degraded to mixtures of diglycerides, either by the action of a lipase or by degradation with a Grignard reagent. The isomeric diglycerides are then resolved with the help of a stereospecific enzyme, either a diglyceride kinase or (after conversion of the diglycerides to phospholipids) a phospholipase. It is then possible to analyze or calculate the fatty acid composition for each position on the glycerol. The key to a successful stereospecific analysis is the preparation of a representative diglyceride mixture by a truly random degradation of the triglyceride. The Grignard degradation is the most reliable method, but it is not always applicable, and it is accompanied by some isomerization of glycerides. There is room for improvement in the method. Analyse of natural fats have shown most of them to be asymmetric, i.e., the composition of fatty acids in position 1 differs markedly from that of position 3. Several rules of fatty acid distribution have become apparent. Presented at the 62 nd Annual AOCS Meeting, Houston, May 1971.     

Pyrolysis of saturated triglycerides

Saturated monoacid triglycerides were pyrolyzed in a flowing atmosphere of helium at 630–650 C, and the products were colleted at low temperature. They were fractionated by thin layer chromatography, according to polarity, and were further resolved and analyzed by gas chromatography, mass spectrometry and IR spectrometry. Alkanes, alkenes, ketones, esters, free acids and cyclic products were identified. Among the latter are probably lactones and substituted dioxanes and dioxolanes, for which structures have been postulated. The parent acid of the triglyceride and the cyclic residual products, after loss of one acid group from the triglyceride, were prominent products. Many products of pyrolysis had structures similar to the major ions produced in the mass spectrum of the triglyceride.     

Relation of triglycerides to phosphoglycerides in fungi

Lipids of the fungiPhycomyces blakesleeanus, Lipomyces lipoferus, Glomerella cingulata andCoprinus comatus have been analyzed by physical and chemical methods. Triglycerides were the largest fraction of all the lipids in these fungi but significant amounts of phosphoglycerides were also present. The presence of relatively large amounts of triglycerides and phosphoglycerides, and the fatty acid patterns of these glycerides, suggests that formation of the tri- and phosphoglycerides involves participation of key intermediates from a common pathway of synthesis. The triglycerides ofGlomerella cingulata have been studied in more detail than those of the other species. It has been found, using preparative thin-layer chromatography and analytical gas-liquid chromatography, thatG. cingulata triglycerides comprise one fraction of saturated and monoenoic fatty acids, another fraction of saturated, mono-, and dienoic acids and two fractions containing varying proportions of saturated, mono-, di-, and trienoic fatty acids.     

Solubilities of five triglycerides in aqueous ethanol

The solubilities of trilaurin, trimyristin, tripalmitin, tristearin, and triolein in 90, 95.4, 98, and 100% ethanol between 40C and 90C were determined. The data were compared with data calculated by the ideal solution law.     

Mechanism of hydrogenation of triglycerides

Factors affecting the rate of hydrogenation, selectivity, and isomerization are discussed in detail. The proposed mechanism for the reaction involves transfer steps for the reactants and products to and from the catalyst surface and the chemical steps occurring on the catalyst surface.     

Lipase-catalyzed synthesis of chiral triglycerides

Under certain reaction conditions, the acidolysis of tripalmitin with oleic acid using immobilized lipase from Rhizomucor miehei resulted in a higher level of monosubstituted oleoyldipalmitoyl (OPP) triglycerides than had been predicted according to kinetic modeling. The reaction products were subjected to chiral analysis by high-performance liquid chromatography (HPLC), which indicated that the enzyme was more active at the sn-1 position of the triglyceride than at the sn-3 position, resulting in synthesis of the chiral triglyceride 1-oleoyl-2,3-dipalmitoyl-sn-glycerol. A kinetic model was developed and was correlated with the HPLC method to provide a simple means to predict the stereoselectivity of lipase-catalyzed reactions. By using the model, the stereoselectivity of immobilized Rhizomucor miehei lipase was found to depend strongly on the initial water activity (a _w) of the reaction mixture, with greater selectivity occurring at lower a _w. The sn-1 selectivity was essentially maintained using various solvents, or without solvent, when a _w was kept constantly low. Variation in the fatty acid composition of the triglyceride indicated that shorter-chain fatty acids result in greater stereoselectivity, while variation of the chainlength of the free fatty acid indicated an enhancement by the longest chainlength. The stereoselectivity of this lipase was confirmed using a new ¹³C nuclear magnetic resonance method. By using immobilized R. miehei lipase at low a _w approximately 80% of the chiral triglyceride found in the reaction mixture was the sn-1 enantiomer, at high reaction conversion.     

Pancreatic lipolysis of enantiomeric triglycerides

Pancreatic lipase hydrolyzed fatty acids in equimolar quantities from thesn-1- and 3-positions of three synthetic enantiomeric triglycerides, two of which could make a racemic pair. The monoglycerides from digestions of five enantiomeric triglycerides were at least 99% representative of the 2-position. The data confirm that pancreatic lipase did not distinguish between thesn-1- and 3-positions and that with these triglycerides pancreatic lipolysis can be used to help establish structure. Scientific contribution No. 419 Agricultural Experiment Station, University of Connecticut, Storrs.     

Quantitative gas-liquid chromatography of triglycerides

To determine optimum operating conditions, an extensive study was made of the variables affecting quantitative recovery and resolution of model triglyceride mixtures. Parameters investigated included: flash heater temperature, carrier gas flow rate, type of carrier gas, column length, glass and metal columns, temperature program rate, linearity of detector response, physical design of gas chromatograph, and molecular species of triglyceride. Results indicate that with optimum operating conditions, triglyceride molecular weights through trierucin can be quantitatively analyzed. Accurate calibration is essential, since quantitative response factors vary somewhat with operating conditions, triglyceride carbon number, and the chromatograph used. Cocoa butter and rat adipose tissue triglycerides have been quantitatively analyzed by this technique. Presented at the AOCS meeting in Houston, Texas, 1965.     

Stereospecific analysis of maize triglycerides

This is the first report of stereospecific analyses of plant triglycerides isolated from seeds of distinct genotypes rather than from commerically refined oils. Triglycerides from six maize inbreds were analyzed. The strains exhibited a wide range of fatty acid compositions (palmitic acid 7.8–19.1%, oleic acid 17.0–43.0%, linoleic acid 41.6–68.3%). The distribution of the fatty acids among the 1, 2 and 3 positions of the triglycerides was clearly nonrandom for all six strains. At the 2 position of the triglycerides over 98% of the fatty acids were unsaturated. More plamitic and stearic acids were found in position 1 than in 3. The general fatty acid pattern of maize triglycerides was similar to that found in most animal triglycerides.     

Nutritional properties of medium-chain triglycerides

The biological effects of MCT (medium-chain triglycerides) differed from those of conventional fats, and certain of these suggested examination of the fatty acid composition and triglyceride structure of the adipose tissues and other organs of rats which were fed medium- or long-chain triglyceride mixtures with two levels of linoleic acid. Fatty acid compositions and TG patterns varied with the tissue, with the dietary fat, and with the level of linoleate in the diet. Increasing the latter resulted in the deposition of more linoleate at the expense of oleate and in the deposition of more of the dietary fatty acids. The percentage of completely saturated triglyc-erides (S₃), in adipose tissue with the higher linoleate supplement in the rats fed MCT, decreased in those fed LCT and was unchanged in the controls fed a fat-free diet. The increased deposition of the dietary fatty acids was more pronounced in the S₃ band. Supported by Grants U-1347 and U-1510 from the Health Research Council of the City of New York.     

Rheology of chemically modified triglycerides

The rheology of chemically modified plant oils was determined to aid in their processing for polymers and other applications. Epoxidized and acrylated triglycerides were derived from various plant oils and model triglycerides. The viscosity of the unmodified oils decreased as the level of oil unsaturation increased. However, the viscosity of the epoxidized oils increased slightly as the level of epoxidation increased. Furthermore, the viscosity of the acrylated oils increased exponentially as the level of acrylation increased because of increased polarity. In addition, the viscosity of the acrylated oils increased as the average distance of the acrylate groups from the fatty acid chain ends decreased. Chemically modified and unmodified oils did not exhibit any shear‐thinning behavior or any memory of shear history. The temperature dependence of the viscosity followed the Arrhenius law, and the activation energy decreased linearly with the level of acrylation. The addition of comonomers, such as styrene, reduced the viscosity of the acrylated oils exponentially as the comonomer concentration increased. However, the glass‐transition temperature and modulus of the triglyceride‐based polymers decreased as the styrene content decreased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 774–783, 2005