Stereoselective hydrogenation of model compounds and preparation of tailor-made glycerides with chromium tricarbonyl complexes

Studies on the mechanism of stereoselectivity of chromium tricarbonyl catalysts with model compounds provided the basis for the preparation of simulated fats. These synthetic fats were prepared by taking advantage of the unique property of chromium carbonyl complexes to catalyze hydrogenation of polyunsaturates tocis-monounsaturates. Oils simulating the composition of peanut oil were produced by hydrogenating soybean oil stereoselectively to an IV of 94. Simulated olive oil was made the same way from either soybean or safflower oil hydrogenated to an IV of 82–84. Stereoselective 1,4-reduction of eleostearate in tung oil produced oils that had a high proportion of linoleate and that simulated safflower oil. The oleo-disaturated glyceride structure of cocoa butter was also simulated by selectively hydrogenating linoleate in cottonseed oil stearines and in fractionated high-palmitate stearines. Dilatometric and chromatographic studies showed that thecis-monoene-disaturated glyceride is the major component (60–70%) in the synthetic cocoa butter. One of 10 papers to be published from the “Symposium Hydrogenation” presented at the AOCS Meeting, New Orleans, April 1970. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Protection of dietary polyunsaturated fatty acids against microbial hydrogenation in ruminants

Polyunsaturated fatty acids are normally hydrogenated by microorganisms in the rumen. Because of this hydrogenation ruminant triglycerides contain very low proportions of polyunsaturated fatty acids. A new process is described whereby polyunsaturated oil droplets are protected from ruminal hydrogenation by encapsulation with formaldehyde-treated protein. The formaldehyde-treated protein resists breakdown in the rumen thereby protecting the fatty acids against microbial hydrogenation. When these protected oils are fed to ruminants the formaldehydeprotein complex is hydrolyzed in the acidic conditions of the abomasum and the fatty acids are absorbed from the small intestine. This results in substantial changes in the triglycerides of plasma, milk and depot fats, in which the proportion of polyunsaturated fatty acids is increased from 2–5% to 20–30%. These effects are observed in the plasma and milk within 24–48 hr of feeding while a longer period is necessary to alter the composition of sheep depot fat. The implications of these findings are discussed in relation to human and ruminant nutrition.     

Isothermal crystallization of hydrogenated sunflower oil: I—Nucleation

Nucleation kinetics of sunflower seed oil, which was hydrogenated under two different conditions, was studied by means of a polarized light microscope and an optical setup with a laser as the light source. When the laser was used, observed induction times were shorter than the ones measured by the microscope. The laser method was found to be more sensitive and accurate. Two different crystallization behaviors were found depending on the chemical composition of the samples. Samples with high content of trielaidin crystallized in the β form at temperatures close to the melting points. They exhibited both β′ and β forms depending on crystallization temperature, as happens in natural semisolid fats such as palm oil. Samples with high content of mixed oleic and elaidic triacylglycerols crystallized in the β′ form even at temperatures close to the melting points and they did not show β form under the conditions used in this study. Activation free energies of nucleation for hydrogenated sunflower seed oil were low for the two hydrogenation conditions. It can be concluded that nucleation of sunflower seed oil is a fast process and initially needs low supercooling. These results are also important from a practical point of view for processing design, especially in regards to processes in which fats should be completely crystallized by the end of the production line.     

Catalytic transfer hydrogenation of soybean oil

The catalytic transfer hydrogenation of soybean oil by various hydrogen donors and solvents with palladium-oncarbon catalyst was investigated in batch and continuous modes. The choice of reaction conditions, donor and catalyst allowed the manufacture of partially hydrogenated oils or semi-solid fats with controlled fatty acid contents, iodine value, melting point and solid content index. The level of “iso” forms of fatty acids was similar to, and average initial selectivity was higher than that obtained with gaseous hydrogenation under pressure with a catalyst of the same type. The best results were obtained in aqueous solution with sodium formate as hydrogen donor at 60°C.     

A process for solid fat from castor oil by simultaneous hydrogénation and dehydration

A single step process has been developed on a pilot plant scale (15 kg/batch) for simultaneous hydrogenation and dehydration of castor oil using nickel catalyst and attapulgite to yield solid fats having a hydroxyl value of 7–33 and an iodine value of 41–56. The polymer and keto fatty acid contents in the products were up to 2% and 3.2%, respectively. The product can be used in the manufacture of soap as the hard fat component and in textile sizing.     

The isomerization of fats during hydrogenation and the metabolism of the component fatty acids

Summary Extensive positional and geometrical isomerization occurs during the catalytic hydrogenation of edible oils and fats. The extent of this isomerization can be controlled by varying the conditions of hydrogenation. Studies on the nutritional and metabolic aspects of the geometric isomers formed during the hydrogenation of edible fats indicate that the animal organism appears to be capable of metabolizingrans isomers. However there is some evidence to indicate that the deposition oftrans fatty acids in animal tissues may worsen a pre-existing essential fatty acid deficiency. Presented at the 32nd fall meeting, American Oil Chemists' Society, October 20–22, 1958, Chicago, Ill.     

Margarine and shortening oils by interesterification of liquid and trisaturated triglycerides

Liquid vegetable oils (VO), including cottonseed, peanut, soybean, corn, and canola, were randomly interesterified with completely hydrogenated soybean or cottonseed hardstocks (vegetable oil trisaturate; VOTS) in ratios of four parts VO and one part VOTS. Analysis of the reaction products by high-performance liquid chromatography showed that at 70°C and vigorous agitation, with 0.5% sodium methoxide catalyst, the reactions were complete after 15 min. Solid-fat index (SFI) measurements made at 50, 70, 80, 92, and 104°F, along with drop melting points, indicated that the interesterified fats possess plasticity curves in the range of commercial soft tub margarine oils prepared by blending hydrogenated stocks. Shortening basestocks were prepared by randomly interesterifying palm or soybean oil with VOTS in ratios of 1:1 or 3:1 or 4:1, respectively. Blending of the interesterified basestocks with additional liquid VO yielded products having SFI curves very similar to commercial all purpose-type shortening oils made by blending hydrogenated stocks. Other studies show that fluid-type shortening oils can be prepared through blending of interesterified basestocks with liquid VO. X-ray diffraction studies showed that the desirable β′ crystal structure is achieved through interesterification and blending. Presented at AOCS Annual Meeting & Expo, Atlanta, Georgia, May 8–12, 1994.     

Continuous hydrogenation of fats and fatty acids at short contact times1

Continuous hydrogenation of fats and fatty acids using suspended catalysts was studied in a vertical flow reactor packed with Raschig rings. A short time of reactive contact of the fat or the fatty acid with the catalyst and hydrogen is the unique feature of this system. A nickel catalyst used in the hydrogenation of soybean oil gave a reduction of 40-50 iodine value units per min, small amounts oftrans-isorners (10-20%), large proportions of linoleate in unreduced octadecadienoyl moieties (70-80%), and nonselective reduction of polyunsaturated acyl moieties (linoleate selectivity ratio 1-3). Another nickel catalyst, used in the hydrogenation of tallow fatty acids, also gave a reduction of 40-50 iodine value units per min and nonselective reduction of polyunsaturated fatty acids. A copper chromite catalyst used in the hydrogenation of soybean oil gave a reduction of 10-15 iodine value units per min, low levels oftrans- isomers (10-15%), and selective reduction of linolenoyl moieties (linolenate selectivity ratio 4-6). Composition of positional isomers of cis- andtrans-octadecenoyl moieties in partially hydrogenated products obtained both with nickel and copper chromite catalysts reveals that essentially the same mechanisms of isomerization are involved in continuous hydrogenation at short time of reactive contact as in batch hydrogenation. 1The terms “linoloyl” and “linolenoyl” are used throughout to designate9-cis, 12-cis-octadecadienoyl and 9-cis, 12-cis, 15-cis- octadecatrienoyl groups, respectively.     

Selective homogeneous hydrogenation of triunsaturated fats catalyzed by tricarbonyl chromium complexes

The need for a selective catalyst to hydrogenate linolenate in soybean oil has prompted our continuing study of various model triunsaturated fats. Hydrogenation of methylβ-eleostearate (methyltrans,trans,trans-9,11,13-octadecatrienoate) with Cr(CO)₃ complexes yielded diene products expected from 1,4-addition (trans-9,cis-12- andcis-10,trans-13-octadecadienoates). Withα-eleostearate (cis,trans,trans-9,11,13-octadecatrienoate), stereoselective 1,4-reduction of thetrans,trans-diene portion yielded linoleate (cis,cis-9,12-octadecadienoate). However,cis,trans-1,4-dienes were also formed from the apparent isomerization ofα- toβ-eleostearate. Hydrogenation of methyl linolenate (methylcis,cis,cis-9,12,15-octadecatrienoate) produced a mixture of isomeric dienes and monoenes attributed to conjugation occurring as an intermediate step. The hydrogenation ofα-eleostearin in tung oil was more stereoselective in forming thecis,cis-diene than the corresponding methyl ester. Hydrogenation of linseed oil yielded a mixture of dienes and monoenes containing 7%trans unsaturation. We have suggested how the mechanism of stereoselective hydrogenation with Cr(CO)₃ catalysts can be applied to the problem of selective hydrogenation of linolenate in soybean oil. No. Market. Nutr. Res. Div., ARS, USDA.     

Homogeneous catalytic hydrogenation of unsaturated fats: Cobalt carbonyl

Homogeneous hydrogenation of unsaturated fats by cobalt carbonyl has been compared with the previously reported catalysis by iron carbonyl. Soybean methyl esters, methyl linoleate and linolenate have been hydrogenated at 75–180C, 250–3,000 psi H₂ and 0.02 molar concn of catalyst. The cobalt carbonyl catalyst is more active at lower temp than iron carbonyl. The partially reduced products are similar to those observed with iron carbonyl, but the reaction differs in showing much less accumulation of conjugated dienes, no selectivity toward linolenate, almost complete absence of monoene hydrogenation to saturates, less double bond migration and moretrans isomerization. No evidence was found for a stable complex between cobalt carbonyl and unsaturated fats as previously observed with iron carbonyl. The rates of hydrogenation/double bond were the same for linoleate and linolenate on one hand, and for alkali-conjugated linoleate and nonconjugated linoleate on the other. Presented at AOCS Meeting in Minneapolis, 1963. A laboratory of the No. Utiliz. Res. & Dev. Div., ARS, USDA.     

Industrial hydrogenation of rice bran oil,a substitute for tallow

The Indian soap industry’s hard fat requirement was met until recent years by imported animal tallows. The search for alternate hard fats, consequent to the ban on the import of animal tallows in 1983, led to realization of the striking similarity in the fatty acid composition of mutton tallow and hydrogenated rice bran oil, except for thetrans oleic acid content. This paper traces the course of compositional changes undergone by rice bran oil during industrial hydrogenation, employing gas liquid chromatography and infra red spectroscopy.     

Blending process optimization into special fat formulation by neural networks

Computer programs are used to manage, supervise, and operate production lines of oil, margarine, butter, and mayonnaise in the fats and oils industry. Automation allows for lower-cost and better-quality products. The present paper shows a multilayer perceptron-type, second-generation neural network that was built based on a desirable product solid profile and was designed to formulate fats from three ingredients (one refined oil and two hydrogenated soybean-based stocks). This network operates with three sequential decision levels, technical, availability and costs, to furnish up to nine possible formulations for the desired product. Upgrading verification was accomplished by soliciting to the formulation network all 63 products used in the upgrading (the answers were evaluated by a panel of experts and considered satisfactory) and 17 commercial products. It was possible to formulate more than 50% of the products in the network with only the three bases available. The results demonstrate the possibility of using neural networks as an alternative to the automation process for the special fats formulation process. Presented at 6th Latin American Congress and Exhibit on Fats and Oils Processing, September 25–28, 1995, Campinas, Brazil.     

The fluorescence of chlorophyll in fats in relation to rancidity

Summary 1.) Difficulties in applying the “chlorophyll value” test to fat samples has led us to investigate the apparent “quenching” of chlorophyll fluorescence in mineral oil solution when cottonseed oil or lard is added to it. The disappearance of chlorophyll fluorescence in ultraviolet light caused by the addition of cottonseed oil appears to be due to the absorption of the light by the cottonseed oil and to the intense white fluorescence of the oil itself rather than to a chemical reaction of some constituent of the oil with the excited chlorophyll. 2.) There was no evidence of a stoichiometric quenching reaction between chlorophyll and acceptor substances in the fats used in this study and, in consequence, no “endpoint” was observed in any of the titrations. 3.) A lack of correlation between either the peroxide value or the stabilities measured in conventional ways and the amount of chlorophyll fluorescence of several fats makes the “chlorophyll value” test appear to have doubtful value as a generally applicable test for fat rancidity or stability. 4.) The crude absorption curves here presented suggest that the greater absorption of near ultraviolet light by oxidized fats may be related to their content of fat peroxides. This work was made possible by grants from the Rockefeller Foundation, the Hormel Foundation, and the Graduate School of the University of Minnesota. Assistance in the preparation of these materials was furnished by the personnel of Work Projects Administration, Official Project No. 165-1-71-440, Subproject No. 382.     

Palm oil and palm kernel oil in food products

Cocoa butter equivalent (CBE) formulation, especially the compatibility of palm oil based CBE with cocoa butter, is of special interest to chocolate manufacturers. Traditionally palm oil is fractionated to obtain high-melting stearin and olein with a clear point of around 25 C, the latter serving as cooking oil. Recently, palm oil has been fractionated to recover an intermediate fraction known as palm mid-fraction (PMF), which is suitable for CBE formulations. Generally, production of PMF is based on a three-step procedure. However, a dry fractionation system, which includes selective crystallization and removal of liquid olein by means of a hydraulic press, has been developed. Iodine value, solid content (SFI) at different temperatures, cooling curves (Shukoff 0°) and triglyceride/fatty acid composition determination confirmed effectiveness of the procedure followed. A direct relationship between yield, quality of PMF and crystallization temperature during fractionation has been achieved. Yield of 60% for olein of IV 64–67 has been achieved. Yield of 30% for PMF of IV 36–38 and 10% for high melting stearin of IV of 20–22 are also being achieved. High-melting stearin may be used in oleochemical applications, soaps, food emulsifiers and other industrial applications such as lubricating oil. Olein fraction, especially after flash hydrogenation thereby reducing the IV to 62/64, has excellent frying and cooking oil characteristics. Palm olein is also suitable as dietary fat and in infant formulation. Studies on interesterification of high-melting stearin with olein showed possibilities to formulate hardstocks for margarine and spread formulations, even without using hydrogenated fat components. Palm kernel and coconut fats or fractions or derived products are used for confectionery products as partial CB replacers and as ice cream fats and coatings. Coconut oil also serves as a starting material for the production of medium-chain triglycerides.     

Hydrogenation of fatty acids

Catalytic hydrogenation is a vital process for both the edible fats and oil and the industrial fatty chemical industries. The similarities and differences between the fat and oil and fatty acid hydrogenations in equipment, processing conditions, and catalysts employed are of some importance since both are used in the various operations. Generally, the catalytic hydrogenation of fatty acids is carried out in corrosion-resistant equipment (316SS), whereas for fats and oils while 316SS is desirable, 304SS or even black iron surffice. The speed of hydrogenation varies radically with the content of impurities in both fat and oil and fatty acid feedstocks. Especially detrimental for both hydrogenations are soap and sulfur contaminants, proteinaceous materials left in the oils from poor refining, etc. Fatty acids from vegetable oil soapstocks are especially difficult to hydrogenate. Soybean-acidulated soapstock must usually be double-distilled for good results; cottonseed soapstocks frequently triple-distilled in order that they can be hydrogenated below iodine values of 1. Fatty acid hydrogenation effectiveness is measured by achieveing a low iodine value as fast and as economically as possible. Variables that influence hydrogenation effectiveness are reactor design, hydrogen purity, feedstock quality, catalyst activity and operating conditions.     

Formulation of products from soybean oil

High quality shortenings and margarines may be produced using soybean oil as the only fat source or using soybean oil as the primary fat source with the addition of a small amount of hydrogenated cottonseed or palm oil to provide crystal stability. These shortenings and margarines are manufactured by direct hydrogenation or by blending hydrogenated and/or unhydrogenated base stocks. The properties of soybean oil preclude the need for processes other than hydrogenation and blending to produce most margarine and shortening products. It is possible to design an integrated base stock program in which a limited number of base stocks may be used jointly in margarine and shortening formulations. This type of base stock program results in fewer hydrogenation department heels and simplifies scheduling of the hydrogenation department as well as scheduling of overall operations. Solid fat index (SFI) is the analysis used for final product consistency control. While base stocks are blended to meet a final SFI requirement, this analysis is too time-consuming to be used in hydrogenation control and individual hydrogenation batches are controlled using refractometer number and congeal points. Finished product characteristics are a result of decisions that must be made regarding characteristics such as plastic range and AOM stability, which are incompatible.     

Analysis and monitoring oftrans-isomerization by IR attenuated total reflectance spectrophotometry

Attenuated total reflectance for IR determination oftrans-isomers in fats appears to have distinct advantages over procedures currently used. The AOCS standard method CD 14-61 requires weighing and quantitative dilution of a sample with carbon disulfide before spectrophotometric analysis at 10.3 μm. In contrast, according to the attenuated total reflectance analytical procedure, one neither weighs nor dilutes but merely fills the cell with oil and reads at 10.3 μm. In addition to analyses fortrans-isomers in liquid oils, margarines and shortenings, attenuated total reflectance enables one to monitortrans-development continuously during hydrogenation. The presence of catalyst in unfiltered hydrogenated oils does not interfere with attenuated total reflectance measurements in contrast to classical transmission measurements. Unfiltered oil from the hydrogenator can be circulated through the attenuated total reflectance cell to recordtrans-isomerization during the reaction. ARS, USDA.     

Formulation of zero-<Emphasis Type="Italic">trans</Emphasis> acid shortenings and margarines and other food fats with products of the oil palm

The fruit of the oil palm yields two types of oil. The flesh yields 20–22% of palm oil (C16∶0 44%, C18∶1 39%, C18∶2 10%). This represents about 90% of the total oil yield. The other 10%, obtained from the kernel, is a lauric acid oil similar to coconut oil. Palm oil is semisolid, and a large part of the annual Malaysian production of about 14 million tonnes is fractionated to give palm olein, which is widely used for industrial frying, and palm stearin, a valuable hard stock. Various grades of the latter are available. Formulae have been developed by straight blending and by interesterification of palm oil and palm kernel oil to produce shortenings and margarines using hydrogenated fats to give the consistency required. Products that include these formulations are cake shortenings, vanaspati (for the Indian subcontinent), soft and brick margarines, pastry margarines, and reduced fat spreads. Other food uses of palm products in vegetable-fat ice cream and cheese, salad oils, as a peanut butter stabilizer, and in confectioners fats are discussed briefly here.     

Analysis of Cod-Liver Oil Adulteration Using Fourier Transform Infrared (FTIR) Spectroscopy

Analysis of the adulteration of cod-liver oil with much cheaper oil-like animal fats has become attractive in recent years. This study highlights an application of Fourier transform infrared (FTIR) spectroscopy as a nondestructive and fast technique for the determination of adulterants in cod-liver oil. Attenuated total reflectance measurements were made on pure cod-liver oil and cod-liver oil adulterated with different concentrations of lard (0.5–50% v/v in cod-liver oil). A chemometrics partial least squares (PLS) calibration model was developed for quantitative measurement of the adulterant. Discriminant analysis method was used to classify cod-liver oil samples from common animal fats (beef, chicken, mutton, and lard) based on their infrared spectra. Discriminant analysis carried out using seven principal components was able to classify the samples as pure or adulterated cod-liver oil based on their FTIR spectra at the selected fingerprint regions (1,500–1,030 cm⁻¹).     

Interchangeability of fats and Oils

The requirement for interchangeability of fats and oils is a result of such factors as availability and cost of raw materials, and the effects of legislation or market preference on product composition. Such changes should not affect the product’s quality or performance. Interchangeability is practiced today in the production of products for human food, animal feed and technical uses, and is frequently controlled by computer. It is necessary fully to identify a product and its essential features whether simply by melting point or a full triglyceride structure. Modern analytical techniques such as NMR, GC, HPLC and DSC have enabled this identification to become a more exact science. The interchange may consist of a simple substitution of one oil or fat for another, or it may be more complex, involving a number of oils and fats and processes. Finally, the nature of the product may be such that it has to be “tailor-made” using sophisticated processes to produce the required triglyceride composition. The unit processes which are employed are blending, hydrogenation, fractionation and interesterification. In the last process the recently published use of enzymes is of particular interest. Problems encountered are mainly concerned with the polymorphism of fats and oils which frequently sets limits on the proportion of a particular fat which can be used. Limits are also imposed by plant processing capacity. Palm and lauric acid oils are particularly important in the context of interchangeability for both edible and technical purposes because of their fatty acid and triglyceride compositions. They provide good examples of usefulness, problems resulting from polymorphism and the difficulties of substitution.