Hydrogenation of soybean oil triglycerides: Effect of pressure on selectivity

Soybean oil contains five triglycerides that account for over 70% of the total. These include LLL, LLO, LLP, LOO, and LOP and their isomers (where L=linoleic, O=oleic, P=palmitic). High-performance liquid chromatographic analysis of samples taken during a typical hydrogenation run in which the iodine value (IV) was reduced from 130 to about 70 showed that the linoleate-containing triglycerides were reduced at a much faster rate than the linolenate-containing triglycerides. Results clearly show that hydrogenation proceeds through definite pathways rather than by random saturation of fatty acids within the triglyceride molecules. Pressure has a significant effect on the course of hydrogenation. At higher pressures (500 psi), the reaction is truly nonselective, since di-and trisaturated glycerides are formed at about 70 IV, whereas at 50 psi, the reaction becomes selective. At higher pressures, fat functionality and solid fat result primarily from di-and trisaturated fatt acid triglycerides as well as trans fatty acid triglycerides. At lower pressures, functionality results from trans acid triglyceride formation. Although the reactivity of linoleate containing triglycerides followed the pattern 6 double bonds>5 double bonds>4 double bonds, other factors may be important. For example, LLP is reactive and undergoes hydrogenation, while LLS remains unchanged. Triolein, which constitutes less than 3% of the total triglyceride in natural soybean oil, is a significant product of hydrogenation, which suggests that LLL and LLO are reduced directly while adsorbed on the catalyst surface. Presented in part at the A.E. Bailey Award Dinner, Peoria, IL, Feb. 23, 1999.     

Effect of randomization on the oxidation of corn oil

Randomized corn oil and corn oil methyl esters both oxidized three to four times faster than natural corn oil. The difference in rate could not be attributed to pro- or antioxidants. Thin layer chromatography of the oxidized oils and methyl esters after reduction with hydrogen iodide revealed two bands moving slower than the original esters. One was shown to be a mixture of scission products; the other was monohydroxy-triglyceride. There was three times more scission products from randomized than natural corn oil. Glyceride structure seems not to affect the rate of oxidation of triglycerides by altering substrate availability. The difference in yield of scission products suggests that glyceride structure may affect the rate of initiation. Journal Paper no. J-10497 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project no. 2143.     

The effect of heat on pure triglycerides

A knowledge of the mechanism of the degradation of triglycerides at temperatures from 190°C. is important in predicting the type of breakdown products likely to be formed in processing oils at elevated temperatures, or in the usage of oils and fats in frying or baking. The effect of heat on tricaprin and 2-oleo-dipalmitin has been studied both in the absence and in the presence of oxygen. The results show that even a pure fully saturated triglyceride is rendered organoleptically unacceptable, due to breakdown in the temperature range studied, although the mechanism differs according to whether oxygen is present or not. Unsaturated glycerides are more readily degraded, fission at or near the double bonds being superimposed on the processes previously established for saturated triglycerides. Many of the degradation products have been identified. Degraded triglycerides can be refined to an acceptable standard by conventional means but their keeping times, in the refined state, are considerably less than those of the original pure materials. Hence, it is inferred that precursors of off-flavors persist in the products and survive the refining operations.     

Effect of randomization on the oxidative stability of corn oil

Randomized corn oil TAG oxidized much faster than natural oil, but after purification with alumina, they oxidized at the same rate. We showed that this effect could not be attributed to a difference, in total tocopherols in the randomized and natural oils. Polar material recovered from the alumina treatment was fractionated by TLC, and a pro-oxidant effect was found in the fractions containing MAG and DAG. However, MAG and DAG, although mild pro-oxidant could not account for the pro-oxidant effect generated by randomization. No other compounds could be detected in the MAG fraction by MS. The pro-oxidant effect of randomized oil disappeared when EDTA or citric acid was added in sufficient amounts. The pro-oxidant effect of randomized corn oil was increased by the incorporation of additional copper or iron at a concentration that did not catalyze oxidation of the purified oil. Treatment of corn oil with ascorbic acid, ascorbyl-6-palmitate, ethyl acetoacetate, ethyl diacetoacetate, and acetylacetone did not reproduce the effect of the unknown pro-oxidant. Although the identity of the pro-oxidant is still unknown, we have confirmed that it is produced during randomization; it does not have pro-oxidant activity alone, but it facilitates the catalytic activity of the transition metal ions.     

Effect of controlled temperature environments on oil content and on fatty acid composition of corn oil

Total oil content and fatty acid composition of germ and endosperm oil were determined on grain from three inbred lines and one variety of corn (Zea mays L.) grown in four phytotron environments and one standard greenhouse environment during seed maturation. Pronounced differences occurred with reversals for relative percentages of oleic and linoleic acids of germ oil for one inbred line and for the variety. Comparative trends were generally less pronounced for two of the inbred lines. Differences among environments were less evident for palmitic, stearic, and linolenic acids of germ oil and for the fatty acids of the endosperm oil. Total oil was lowest for two inbred lines and the variety grown in the high temperature environment (30 C day/26 C night). The magnitude of temperature effects on oil content and oil composition varied among the four corn genotypes. Journal article 3961 of the North Carolina State University Agricultural Experiment Station. ARS, USDA.     

The component triglycerides of palm-kernel oil

Triglycerides of palm-kernel oil were fractionated by gas liquid chromatography into 13 groups based on their carbon number of 30 to 54. These groups represent 99.9% of the total glyceride content. The proportion of triglyceride types in each group was calculated from the component fatty acids. These groups are defined by the nature of their constituent fatty acids but the position of the acids on glycerol is unknown. These 87 types, 24 of which are given in detail, were found. The two major components are trilaurin (19.8%) and dilauromyristin (14.1%). Only 18 types, occurring in an amount greater than 1%, together represent 80% of the total glycerides. Comparison of the glyceride content with that of coconut oil revealed many similarities between the two oils.     

Estolide triglycerides ofTrewia nudiflora seed oil

The seed oil ofTrewia nudiflora is known to contain glycerides of α-kamlolenic (18-hydroxy-cis-9,trans-11,trans-13-octadecatrienoic) acid. We have shown that a large part of these glycerides contain estolides in which the hydroxyl group of α-kamlolenic acid is esterified to a molecule of another acid, either a hydroxy acid or an ordinary fatty acid. By preparative thin layer chromatography, we isolated a series of tri-, tetra-, penta- and hexaacyl glycerols. By lipolysis and gas chromatography-mass spectrometry, we isolated and characterized estolide-linked fatty acids containing two acid moieties.     

Composition of corn oil

The composition of commercial corn oil from USA corn is remarkably constant. A total of 103 samples of refined corn oil produced over a period of 2.5 years were analyzed by the alkali isomerization procedure. Nearly 86% of the samples had an iodine value (I.V.) within one unit of the average value, 123.6. Linoleic content on a fatty acid basis, averaged 55.5%; 93% of the values were within two units of this value. All samples contained small amts of linolenic acid. This uniformity undoubtedly results from the system of corn marketing and buying which brings grain from the entire corn belt to the processing plants. A number of corn oils were analyzed by GLC. The average linoleic acid content by this method was ca. 2.5 units higher than that found by the isomerization method. This difference may occur because GLC responds to all C-18 dienes equally while the alkali isomerization method responds only to conjugatable dienes. Possible sources of error in both methods of fatty acid analysis are discussed. Corn oil samples taken over a 16-month period were analyzed by GLC. Although much of our experience has been with the alkali isomerization method, the GLC technique is preferred because it is simpler and yields more information on fatty acid composition. Another important advantage is that determination of the I.V. of the oil serves as a check on GLC results. The I.V. calculated from the GLC results, making allowance for 1.25% unsaponifiables in the case of corn oil, should be within a few units of the Wijs value. Oils derived commercially from corns grown in other countries are generally more saturated than those from USA corn. The I.V. of the samples examined varied from 107–125, the linoleic acid contents from 42–56%. The relationship between I.V. and linoleic acid content established by others from hybrid corns holds fairly well for these samples.     

Hydroxymethylation and polymerization of plant oil triglycerides

The ene reaction between plant oil triglycerides (such as soybean and sunflower oils) and paraformaldehyde was used to introduce a homoallylic hydroxyl functionality on the triglyceride. Paraformaldehyde and triglyceride were reacted in the presence of a Lewis acid catalyst, ethylaluminum dichloride, and hydroxymethyl derivatives were obtained at yields of 42 and 55% for sunflower oil and soybean oil, respectively. In the next step, hydroxymethyl products were reacted with maleic anhydride at 100°C to produce the maleate half esters. The average number of maleate groups per triglycerides was found to be 1.7 for soybean oil and 1.3 for sunflower oil. In the final step, the free‐radical–initiated copolymerization of the maleinized triglycerides with styrene produced rigid polymers. Characterization of new monomers and polymers was done by ¹H‐NMR, ¹³C‐NMR, and infrared and mass spectrometries. The swelling behavior of the crosslinked network polymers was determined in different solvents. The glass‐transition temperature of the cured resin was also determined by differential scanning calorimetry to be 40°C for soybean‐based polymer and 30°C for sunflower‐based polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4037–4046, 2004     

Characterization of triglycerides isolated from jojoba oil

Triglyceride compounds isolated from jojoba seed oil by column chromatography were composed predominantly of C_18′ C_20′ C_22′ and C₂₄ n−9 fatty acids with minor amounts of saturated C₁₆. Chain length and double-bond positions were determined by gas-liquid chromatography and gas-liquid chromatography-mass spectrometry of the corresponding methyl ester and picolinyl ester derivatives. Triglyceride structures were analyzed directly by ion trap mass spectrometry. The analysis of minor compounds, can provide highly specific information about the identity of an oil.     

Effect of heat on the color of trichloroethylene-extracted cottonseed oil

Summary Trichloroethylene cottonseed oil miscellas from prime meats heated during desolventization above 180°F. produced a refined oil darker than prime. When the miscellas were heated above 190°F., the bleached oils produced from them were darker than prime. Extracting prime meats with trichloroethylene above 118°F. produced an oil darker than prime. There is some evidence that heating the meats above about 170°F. also gives a dark oil. Dilute miscellas, when desolventized, produced a darker oil than more concentrated ones probably because of the longer time required for solvent removal. It is believed that the darkening is primarily a function of time and temperature, rather than the solvent used. Formerly Graduate Assistant, Iowa Engineering Experiment Station, Iowa State College, Ames, Iowa     

Changes in structure of triglycerides from maturing kernels of corn

Kernels of corn inbred H51 were collected at five intervals after hand pollination. The triglyceride content of the total lipids increased from 8.6% at 10 days after pollination to 78.3% at 60 days. The most active period of triglyceride synthesis occurred from 20 to 45 days after pollination, when the weight of triglycerides per kernel increased from 1.1 to 7.5 mg. Over all the collection periods the percentages of palmitic, linoleic and linolenic acids decreased while oleic acid increased, but from 30 to 60 days after pollination the fatty acid composition of the triglycerides was nearly constant. Stereospecific analysis revealed a general fatty acid pattern for the triglycerides, in which the concentration of the saturated acids was highest in position 1, linoleic acid in 2 and oleic acid in 3. From 20 to 60 days after pollination there was little change in the fatty acid composition at the 1 position, but the largest changes occurred at the 3 position where palmitic and oleic acids decreased 5.1% and 7.3%, respectively, and linoleic acid increased 13.4%. The variations in the molecular species of the triglycerides were determined by silver nitrate thin layer chromatography and were found to be small from 20 to 60 days after pollination, except for an increase in trilinolein from 5.2 to 11.9%. Stereospecific analyses of four major triglycerides species, SMD, M₂D, SD₂, and MD₂, revealed larger changes in fatty acid distribution at individual positions during maturation than were apparent from analyses of the total triglycerides. Presented in part at the AOCS Meeting, Ottawa, September 1972.     

Rheology of vegetable oil analogs and triglycerides

The rheological properties of two complex mixtures of short-chain triglycerides were experimentally determined. Dynamic or absolute viscosities of the mixtures were measured for shear rates of 0.32 to 64.69 s⁻¹ at temperatures between 25 and 80°C. The compositions of the mixtures were based on the oil of the plant species Cuphea viscosissima VS-320, a natural source of short-chain triglycerides. The dynamic viscosities of these mixtures were compared to those of a traditional vegetable oil (peanut oil) and diesel fuel. The results of this comparison were used to make estimates of the performance of such triglyceride mixtures as diesel fuel substitutes, since viscosity can be a key indicator of fuel performance for possible substitute diesel fuels. The crystallization temperatures of these two mixtures were also determined experimentally, and the effects of crystallization on fuel performance were projected. Additionally, the dynamic viscosities of pure triglycerides from C6∶0 to C18∶0 at 75°C were plotted vs. chain length. These viscosities were measured at high shear rates (>6 s⁻¹) where dynamic viscosity is shear-independent. An obvious trend in the relationship between triglyceride chain length and viscosity was observed. A second-order regression was used to obtain an equation for this relationship. This equation was used as a model for composition dependence of viscosity. This model was applied to the viscosities of the triglyceride mixtures examined here. There was good agreement between the model and the actual, measured viscosity values determined in this study.     

Effect of heat and frying on sunflower,oil stability

Sunflowers are one of the most important sources of vegetable oils in the world, second only to soybeans. Although in use throughout many parts of the world, sunflower seed are just now beginning to attact attention and use in the United States. Composition of the oil appears to be dependent on area of production. Sunflower oil from seed grown in northern US typically contains 70% linoleic acid. In contrast, oil from seed produced in the South generally contains 40–50% linoleic acid and is higher in mono-unsaturated fats. For most of the edible oil market, sunflower oil appears to have an advantage over most other vegetable oils. Lightly hydrogenated sunflower oil was compared with a cottonseed-corn oil mixture for frying potato chips. Organoleptic evaluation indicated that chips did not differ significantly. We also evaluated the useful life of various sunflower seed oils for deep-fat frying. Hydrogenated and unhydrogenated sunflower oils and a commercial shortening were used to deep-fry raw potatoes. A plot of the log of the Active Oxygen Method (AOM) values of the oils versus time gave a straight line, the slope of which reflects the oxidizability of the oil. Data indicated that lightly hydrogenated northern sunflower oil was much less prone to oxidation after abuse than the commercial shortening and was useful for a longer time. The southern oil deteriorated faster than the northern sunflower oil, but the two oils were processed differently. Thus, in recent work, care was taken to process both northern and southern grown sunflower seed under identical conditions. Frying studies indicated that oil from southern grown seed was more stable than that from northern seed as would be expected from their fatty acid composition.     

Effect of heat treatments on the volatile composition of coconut oil

Fresh coconut oil was heated under different conditions for 48 hr at 180 C. The heat treatments included heating in vacuo, heating in air and heating in air and water. The samples were distilled under high vacuum and the volatiles thus obtained were analyzed by combined gas chromatography-mass spectrometry. In all heated samples, a series of n-alkanes and I-alkenes, n-alkanals, methyl alkanones, alkenals, gamma-and delta-lactones, methyl and ethyl esters and free fatty acids were identified. The relative amounts of these compounds varied with the type of heat treatment to which the coconut oil was subjected.     

Synthesis of triglycerides from fish oil fatty acids

The generally accepted methods for the synthesis of triglycerides are unsatisfactory when they are applied to highly unsaturated systems such as those present in fish oil. The methods either fail to g ive sufficiently high yields, or they are prohibitive in cost when applied to large scale production. Of the numerous reactions studied, the most feasible was the zinc-catalyzed esterification of fish oil fatty acids with glycerol. Thinlayer chromatography (TLC) showed that this reaction gave yields of 75–78% triglycerides. Gas-liquid chromatography (GLC) demonstrated the composition of the triglycerides was essentially the same as that of the original fatty acids.     

Stereospecific analysis of triglycerides fromMonnina emarginata seed oil

InMonnina emarginata seed oil triglycerides, more than two-thirds of theS-coriolic (13l-hydroxy-cis-9,trans-11-octadecadienoic) acid occurs in position 3 (relative tosn-glycerol). All but a trace of the remainder is in position 1. Presented at AOCS Meeting, Houston, May 1971. N. Market. Nutr. Res. Div., ARS, USDA     

Effect of high fat corn oil,olive oil and fish oil on phospholipid fatty acid composition in male F344 rats

Epidemiological and laboratory animal model studies have provided evidence that the effect of dietary fat on colon tumorigenesis depends on the amount of fat and its composition. Because of the importance of the composition of dietary fat and of tissue membrane fatty acid composition in tumor promotion, experiments were designed to investigate the relative effects of high fat diets rich in ω3, ω6 and ω9 fatty acids and colon carcinogen on the phospholipid fatty acid composition of liver, colon, small intestine, erythrocytes and blood plasma. At 6 wk of age, groups of animals were fed diets containing 5% corn oil (LFCO), 23.5% corn oil (HFCO), 23.5% olive oil (HFOO), and 20.5% fish oil plus 3% corn oil (HFFO). Two weeks later all the animals except the vehicle-treated animals received azoxymethanes.c. once weekly for 2 wk at a dose rate of 15 mg/kg body weight. Animals were sacrificed 5 d later and liver, colon, small intestine and erythrocytes and blood plasma were analyzed for phospholipid fatty acids. The results indicate that the phospholipid fatty acid composition of liver, colon and small intestine of HFCO diet fed animals, were not significantly different from those fed the LFCO diet. The levels of palmitoleic acid and linoleic acid were increased in erythrocytes and blood plasma of the animals fed the HFCO diet compared to those fed the LFCO diet. Feeding the HFCO diet significantly increased the oleic acid content and decreased the linoleic acid and arachidonic acid levels in various organs when compared to the HFCO diet. Animals fed the HFFO diet showed a marked increase in eicosapentaenoic acid and docosahexaenoic acid and a decrease in linoleic acid and arachidonic acid levels as compared to those fed the HFCO diet. The results also indicate that carcinogen treatment had only a minimal effect on the phospholipid fatty acid composition.     

Kinetics of base-catalyzed transesterification of triglycerides from Pongamia oil

The kinetics of transesterification of Pongamia oil using methanol at 60°C were studied. The forward as well as the reverse rate constants of all three steps involved in the transesterification of Pongamia oil are reported for the first time. Among the forward rate constants, the one governing the conversion of TG to DG was the highest and the one for DG to MG was the lowest. A distinct feature of the present work is the direct estimation of the equilibrium constants of all three steps by measuring the concentrations of TG, DG, and MG at very long reaction times. This reduced the number of parameters to be, determined from the kinetic data by one-half, thereby leading to more accurate estimation of the rate constants. The equilibrium constant of the final step involving the conversion of MG to methyl ester and glycerol was at least an order of magnitude greater than that of the first two reaction steps. A detailed comparison was made with kinetic parameters reported in literature. The trend in the relative magnitudes of the rate constants appears to be unique to Pongamia oil.     

Effects of thermally oxidized triglycerides on the oxidative stability of soybean oil

Soybean oil purified by silicic acid column chromatography did not contain peroxides, free fatty acids, phospholipids or oxidized polar compounds. The purified soybean oil was thermally oxidized at 180°C for 96 hr in the presence of air. The thermally oxidized compounds (31.3%) were separated from the purified soybean oil by gradient elution silicic acid chromatography. Thermally oxidized compounds contained hydroxyl groups, carbonyl groups andtrans double bonds according to the infrared spectrum. Thermally oxidized compounds were added to soybean oil and purified soybean oil at 0, 0.5, 1.0, 1.5 and 2.0% to study the effects of these compounds on the oxidative stability of oil. The oxidative stabilities of oils were determined by gas chromatographic analysis of volatile compound formation and molecular oxygen disappearance in the headspace of oil bottles. The thermally oxidized compounds showed prooxidant effects on the oxidative stabilities of both refined, bleached and deodorized soybean oil and purified soybean oil. Duncan’s Multiple Range Test showed that thermally oxidized compounds had a significant effect on the volatile compound formatiion and oxygen disappearance in the headspace of oil at α=0.05.