WO1991008677A1

WO1991008677A1 - Margarine oils having both low trans- and low intermediate chain saturate content

Info

Publication number: WO1991008677A1
Application number: PCT/US1990/007410
Authority: WO
Inventors: Robert C. Dinwoodie; Michael T. Dueber; R. G. Krishnamurthy; James J. Myrick; David K. Hayashi
Original assignee: Kraft General Foods, Inc.
Priority date: 1989-12-18
Filing date: 1990-12-13
Publication date: 1991-06-27
Also published as: IT1242182B; GB2239256B; IT9048587A0; GB2239256A; IE65886B1; IT9048587A1; GB9027077D0; KR910011143A; IE904394A1; AU6979491A; CA2031936A1

Abstract

Transesterified margarine oil products having smooth mouthfeel and broad melting range characteristics which contain very low C8-C16 saturated fatty acids and low $i(trans)-unsaturated fatty acid content, as well as enzymatic methods for preparing such margarine oil products.

Description

MARGARINE OIL8 HAVING BOTH LOW TRANS¬ ACT) LOW INTERMEDIATE CHAIN SATURATE CONTENT

Background of the Invention The present invention is directed to margarine oils, and more particularly is directed to margarine oils having both low trans- acid content and low content of intermediate chain saturated fatty acids, together with margarine-type thermal melting characteristics and/or smooth organoleptic consistency.

Margarine oils are predominantly mixtures of triglycerides which have a plastic consistency at refrigeration and/or ambient temperature, but which have the essential characteristic of melting readily and with substantial completeness in the mouth of the consumer. Such a melting characteristic requires a solid fat index which has an extended gradient over a broad temperature range. In addition, margarine oils must have a crystal size and shape which provides a smooth organoleptic consistency without graininess or similar mouthfeel defects in homogeneity. Margarine oils are distinguished from plastic shortenings, which typically have a high stearic acid content and a melting point higher than body temperature, which is characterized by the presence of substantial solid fat content at body temperature. The high solid fat content at body temperature is desirable in plastic shortenings for use in various hot dishes, or in dispersed form in products such as pastries and baked goods where the high solid fat content is not deleterious. However, a residue of solid fat such as that present in conventional plastic shortenings which fails to melt at body temperature, imparts to a margarine oil an unacceptable waxy sensation in the mouth. As used herein, the term "margarine oil" and "margarine fat" are used interchangeably. Coconut oil and the other oils of the lauric acid type have a relatively low melting profile as a result of their relatively high concentration of intermediate chain saturated fatty acids and may conventionally be utilized as a component of margarine oils. By "intermediate chain saturated fatty acid" is meant an edible saturated fatty acid having from 8 to 16 carbon atoms, particularly including palmitic, myristic and lauric acids or mixtures thereof. Because the melting points of saturated fatty acids exhibit a progressive increase as the carbon chain is lengthened, fats of the coconut oil type which contain relatively large proportions of Cg to C₁₆ saturated fatty acid moieties, have lower melting points than fats with an equivalent degree of unsaturation that comprise a high proportion of C₁₈ fatty acid glycerides. However, intermediate chain dietary saturated fatty acids, notably lauric, myristic and palmitic acids common to lauric acid oils and many natural and processed food products, have been reported in the medical literature as being a factor in the production of plasma cholesterol in populations at risk for coronary heart disease. However, stearic acid although it is a saturated fatty acid, has been reported to have minimal or even reducing effect on cholesterol level ["Effect of Dietary Stearic Acid on Plasma Cholesterol and Lipoprotein Levels", Bonano e, et al., New England Journal of Medicine, Vol. 318, 1244-1271 (1988)]. Accordingly, although.lauric acid oils have desirable margarine oil properties, margarine oils which have low intermediate chain fatty acid content would be desirable.

Vegetable oils, such as cottonseed, peanut, sesame, corn and sunflower oils, and other liquid oleic-linoleic acid oils, as well as soybean oil, may be partially hydrogenated for the production of margarine oils of the requisite melt and consistency characteristics of broad thermal melting range, substantially complete melting at body temperature, and smooth organoleptic characteristics. The desired consistency is typically obtained by blending two or more partially hydrogenated vegetable oils, or blending liquid (unhydrogenated) vegetable oil with a partially hydrogenated vegetable oil. However, conventional partial hydrogenation of vegetable oils containing unsaturated acids, depending on catalyst selectivity, degree of hydrogenation and other processing variables, may produce substantial amounts of unsaturated fatty acids of trans-, rather than cis- configuration. Margarine oils which contain minimal amounts of such trans- acid moieties, together with the requisite solid fat index thermal profile, smooth organoleptic consistency and low intermediate chain fatty acid content, would be desirable.

The main components of margarine oils are triacylglycerols (triglycerides) which are triesters of glycerol and various saturated and unsaturated fatty acids. The physical properties of fats and oils are, to a large extent, determined by the characteristics of the individual fatty acid moieties and by their distribution within the triglyceride molecule. Interesterification is a technique which may be used to alter the fatty acid composition and distribution and therefore the physical properties of triglyceride mixtures. In such processes, chemical catalysis by sodium metal or a sodium alkoxide is used to promote the migration of fatty acyl groups between and within glycerol molecules, so that the product consists of acylglycerol mixtures in which the fatty acyl groups are randomly distributed among the glyceride molecules. The use of enzyme catalysts, such as site specific Upases permits formation of novel, functional fats which cannot be obtained by conventional chemical processes.

A vide variety of transesterification and interesterification procedures are known using inorganic or enzymatic catalysts to achieve redistribution of the esterified fatty acid moieties of triglyceride oils. Such procedures have not been applied to the production of margarine oils having a minimal content of intermediate carbon saturated fatty acids, together with minimal trans- acid components, the requisite solid fat index thermal profile and smooth organoleptic consistency.

Margarine oil products which have the requisite broad range of consistency parameters, together with minimal trans- acid and intermediate chain saturated fatty acid content may be desirable, and it is an object of the present invention to provide such margarine oils. These and other objects of the invention will become more apparent from the following detailed description and the accompanying drawings.

Description of the Drawings

FIGURE 1 is a process flow diagram for an embodiment of a single step batch or cocurrent continuous reaction method for producing a margarine oil in accordance with the present invention having a minimal content of unsaturated fatty acids of trans- configuration and intermediate chain saturated fatty acid;

FIGURE 2 is a process flow diagram for a continuous countercurrent reaction method for producing a margarine oil having a minimal content of unsaturated fatty acids of trans- configuration and intermediate chain fatty acids;

FIGURE 3 is a high pressure liquid chromatographic elution chart representing the triglyceride composition of initial soybean oil used in preparing a margarine oil in accordance with the present invention; and

FIGURE 4 is a high pressure liquid chromatographic elution chart representing the triglyceride composition of a margarine oil in accordance with the present invention prepared from the soybean oil of FIGURE 3.

Description of the Invention

The present invention is directed to margarine oils having both low trans- acid and intermediate chain fatty acid content, together with a broad margarine type solids fat index melting profile and a smooth organoleptic consistency. The present invention is also directed to methods for producing such margarine oils.

As indicated, the margarine oils are provided in accordance with the present invention have a low trans- acid content. By "trans- acid" is meant an unsaturated fatty acid having a carbon chain length of from 16 to 24 carbon atoms and having at least one unsaturated carbon-carbon bond which is in trans- configuration. In conventional margarine oil products prepared from partially hydrogenated vegetable oil, the trans- acid content may exceed 25 weight percent or more of the margarine oil composition, as a result of the partial hydrogenation conditions appropriate to providing a solid fat index of the margarine oil type. In this regard, the margarine oils in accordance with the present invention, comprise less than 6 and preferably less than 3 weight percent of esterified trans- unsaturated fatty acid moieties, based on the total weight of the margarine oil. Such oils may be provided which have less than 2, and even less than 1 weight percent of trans- unsaturated fatty fatty acid moieties, based on the total weight of the margarine oil. As used herein, the weight percentage of trans- unsaturated fatty acids is determined in accordance with AOCS official test Cd 14-61 (1984). Also, as used herein, the weight percent of saturated or unsaturated fatty acid moieties in a margarine oil or vegetable oil glyceride composition is calculated based on the total weight of the fatty acids contained in the margarine oil. As used herein, when referring to weight percent of one or more fatty acid moieties of a margarine oil, the weight percent is calculated based on all of the fatty acid moieties of the margarine oil being hydrolyzed to free fatty acid. The weight percent of one or more species of fatty acid moiety is then calculated as the weight percent of such one or more species based on the total weight of free fatty acids. AOCS official method Ce 1-62 (81) may be used to determine the weight percent of respective fatty acid moieties of a margarine oil.

As also indicated, the margarine oil product has a minimal amount of intermediate chain saturated fatty acid moieties. In this regard, the margarine oil product comprises less than about 6 weight percent and preferably less than about 3 weight percent of intermediate chain saturated fatty acids based on the total weight of the product. Specifically, the total content of palmitic, myristic, or lauric acids, or mixtures thereof, in free or esterified form, is less than 6 percent of the total weight of the fatty acid content of the margarine oil product and preferably less than half this amount, or less than 3 weight percent.

Further in accordance with the present invention, margarine oils are provided which have a broad profile of triglycerides of unsaturated C₁₈ fatty acids in esterified form which produce a wide variety of glyceride components of the oil. In this regard, the margarine oil has an esterified linoleic acid moiety content of from about 25 to about 45 weight percent and preferably from about 30 to about 40 weight percent and from about 0 to about 11 weight percent of esterified linolenic acid moieties and preferably from about 3 to about 5% linolenic acid moiety. Linolenic acid may generally be provided as a component of the soy oil or other linolenic acid containing oils used as a starting material. Further in accordance with the present invention, the margarine oil has an oleic acid content of from about 5 to about 25 weight percent and preferably from about 10 to about 20 weight percent. Moreover, the margarine oil comprises from about 84 to about 95 weight percent of triglycerides, and preferably from about 88 to about 92 weight percent triglycerides. The margarine oil of the invention has relatively high diglyceride content, which is believed to contribute to the smooth organoleptic properties and the solid fat melting index profile characteristics of the product. In this regard, the diglyceride content of the oil will generally be in the range of from about 5 to about 16 weight percent and preferably from about 8 to about 12 weight percent. The monoglyceride component is generally less than about 1 weight percent and preferably is less than about 0.5 weight percent, based on the total weight of the margarine oil product. The weight percent of onoglycerides and diglycerides is determined based on the actual weight of the mono and/or diglyceride component, as a percentage of the total weight of mono, di and triglycerides of the margarine oil composition.

It is an important aspect of the present invention that the fatty acid distribution of the margarine oil of the present invention is non-random, and is distributed differently among the 1-, 3- positions of the glycerine component and the 2- position of the glycerine component. In this regard, the esterified stearic acid is predominantly distributed in the 1-, 3- positions, while esterified unsaturated fatty acid moieties are in higher concentration at the central 2- position of the glyceride molecules. This non-random selective distribution prevents high concentrations of tristearin from forming in the margarine oil. This places the stearic acid moieties at the exterior of the molecule, and concentrates the unsaturated fatty acid component at the internally shielded and more sterically hindered central 2- position. In addition, the hydroxyl groups are non-randomly distributed in favor of the same 1- and 3- positions at which the high melting stearic acid moieties are concentrated, reducing potential distearate concentration. The weight percentage of the principal fatty acid components of the margarine oils of the present invention, at each of the respective l-,3- and 2- positions, is as follows: l-,3- Glyceride 2- Glyceride positions position weight percent weight percent

Palmitic acid 5-10 0-2.0 Stearic acid 50-70 0-5.0 Oleic acid 5-15 20-30 Linoleic acid 10-30 60-80 Linolenic acid 0-10 3-12

As indicated, an important aspect of the present invention is the provision of a broad melting range and smooth organoleptic characteristics. The margarine oil should have a solid fat index which decreases from a value in the range of from about 7 to about 31 percent at 10* C. , a typical refrigeration temperature, to a value of less than three percent at 38.7* C, a value slightly higher than body temperature. Margarine oils in accordance with the present invention are characterized by margarines with solid fat index profiles as follows:

Dilatometric

Solid Fat

Temperature Index Percen

10* C. 7-31 21.1^* C. 3-25 26.7* C. 0.75-10 33.3' C. 0.5 - 4 38. T C. less than 3

The specified solid fat indexes at the specified temperatures are measured by dilatometric methodology in accordance with AOCS procedure Cd 10-57. The dilatometric procedure measures volume changes in the margarine oil as a function of temperature, which changes are a function of the relative proportion of solid and liquid fats. The solid fat index is a dilatometric index on a percentage scale of 0 (for no solid fat) to 100 (for all solid fat) .

Different types of particularly desirable margarine oil having, respectively, a firm bodied (or "stick") consistency and a soft bodied (or "tub") consistency at refrigeration temperature, may be provided in accordance with the present invention. A particularly preferred margarine oil is a firm bodied margarine oil having a solids fat index characterized by having a melting dilation range from about 23 to about 31 at 10* C. (50* F.), and preferably from about 26 to about 27.6 at 10* C. At 21.1* C. (70* F.), the firm bodied margarine oil composition has a melting dilation range from about 15 to about 25 and preferably from about 21 to about 22.6. At 26.7* C. (80* F.), the firm bodied margarine oil composition has a melting dilation range from about 6 to about 10, and preferably from about 8 to about 9. At 33.3' C. (92* F.), the firm bodied margarine oil composition has a melting dilation range from about 0.5 to about 4 and preferably from about 1.9 to about 2.9, and at 38.7* C. (100^* F.), the firm bodied margarine oil composition has a melting dilation range from about 0 to about 3 and preferably less than 2.

A soft-bodied or "tub" margarine oil product may also be provided in accordance with the present invention. A soft-bodied margarine oil in accordance with the present invention will a melting dilation range from about 7 to about 12 and preferably from about 9.5 to about 10.5 at 10* C. At 21.1* C. (70* F.), the soft-bodied margarine oil composition has a melting dilation range from about 3 to about 10 and preferably from about 5 to about 8. At 26.7* C. (80* F.), the soft-bodied margarine oil composition has a melting dilation range of from about 0.75 to about 8, and typically from about 1 to about 7, preferably about 2 to about 4. At 33.3* C. (92* F.), the soft-bodied margarine oil composition has a melting dilation range from about 0.5 to about 3 and preferably from about 0.7 to about 1.2. At 38.7* C. (100* F.), the margarine oil composition has a melting dilation range from about 0 to about 1.5 and preferably less than about 0.8.

The low trans- acid and low intermediate chain saturated acid margarine oils of the present invention may be provided using immobilized enzyme systems and an inexpensive oil source such as soybean oil in a precise sequence of transesterification, separation, full hydrogenation of fatty acids liberated during transesterification and recycle steps. By "transesterification" is meant an exchange of fatty acid

jyrv.

Generally in accordance with the present invention, the margarine oil may be provided by enzymatic transesterification of an edible liquid vegetable oil comprising at least about 73 and preferably 80 weight percent of eighteen carbon fatty acid moieties (C₁₈ saturated and unsaturated fatty acids) , and more preferably at least about 85 weight percent of C₁₈ fatty acid moieties based on the total weight of the edible liquid vegetable oil such as soybean oil. Such C₁₈ fatty acid moieties include stearic acid, oleic acid, linoleic acid and linolenic acid. In addition, the edible liquid vegetable oil should comprise less than 5 and preferably less than 1 weight percent of esterified palmitic acid in the 2- glyceride position, and less than 2.5 and preferably less than 0.5 weight percent of esterified stearic acid in the 2- glyceride position.

The liquid vegetable oil may desirably further comprise at least about 15, and more preferably at least about 22 weight percent of esterified oleic acid in the liquid vegetable oil. In addition, the liquid vegetable oil will preferably comprise at least about 20 weight percent of esterified linoleic acid, and at least about 0.25 and preferably at least 5 percent of esterified linolenic acid. Moreover, the liquid oil should contain less than 2 weight percent, and preferably less than 1 weight percent of esterified stearic acid in the 2- position. As will be discussed, the limited content of stearic acid in the 2- position limits the possible formation of high melting tristearin. Sunflower, soybean, safflower, corn, soy and canola (low erucic acid rapeseed) oils or blends thereof may also be used as starting material for the manufacture of margarine oils in accordance with the present invention. Soybean oil is a particularly preferred starting material. High oleic acid oils, such as high oleic (e.g., having greater than 80% oleic acids) , sunflower, safflower, olive oil do not by themselves provide margarine oils in accordance with the present invention because the solids fat index distribution does not produce the finished oil characteristics. The low linoleic acid content of such oils produces a sharper melting point which is undesirable. These oils must therefore be interesterified in combination with linoleic oils, such as standard sunflower, safflower, corn, cottonseed or mixtures thereof.

The transesterification reaction is carried out by directed enzymatic transesterification of the liquid vegetable oil starting material with a relatively high proportion of stearic acid, using a 1-, 3- positionally specific extracellular lipase enzyme. Extracellular microbial lipases are generally of three types, depending upon their specificity. Some lipases are generally nonspecific, both as regards the position on the glycerol molecule which is hydrolyzed or esterified, and the nature of the fatty acid released or esterified. Depending on the reaction conditions, such lipases catalyze the nonselective hydrolysis, alcoholysis and/or esterification (including transesterification) of fatty acid triglycerides. The lipases produced by Candida cylindracae. also known as £. ruoosa (Benzonana, G. and S. Esposito, Biochi . Bioohv. Acta. 231:15 (1971)), Corynebacterium acnes. (Hassing, G.S., Ibid. 242:381 (1971)), and Staphylococcus aureus. (Vadehra, D.V., Lipids 9:158 (1974)), are examples of such nonspecific lipases. Such lipases are not utilized in the present methods, because they do not provide the non-random distribution required by the margarine oils of the present invention.

The 1-, 3- positionally specific lipases utilized in the present invention constitute a second type of lipases which act on the outer, 1- and 3- positions of the glycerol or triglyceride molecule. When a l-,3- positionally specific lipase is used to catalyze the interesterification of a mixture of triglycerides or a mixture of triglyceride plus free fatty acid or monoester, the action of the enzyme is substantially confined to the 1- and 3- positions of the glycerol. The lipases of Rhizopus delemar and Mucor miehei are examples of l-,3- positionally specific lipases.

A particularly preferred enzyme is an immobilized Mucor miehei lipase (NOVO Lipozyme 3A) such as described in European Patent Application 0140542, which is incorporated by reference herein. A third group of lipases has substantial selectivity for certain long chain unsaturated fatty acids having a cis- double bond at the 9- position of the fatty acid (from the carboxylate group) , and are also not used in the present methods.

The manufacturing processes for preparing the low trans- fatty acid, low intermediate chain saturated fatty acid margarine oils may be carried out in batch mode, or in continuous cocurrent or countercurrent mode. Batch processes may be carried out in a single transesterification step or multiple steps. The use of multiple steps permits use of lower stearic acid/liquid vegetable oil ratios in each step, but requires multiple separation steps. Single step batch or cocurrent continuous processes require relatively high ratios of stearic acid to liquid vegetable oil in the initial reaction mixture, but are generally more economical than multi-step processes.

In accordance with such manufacturing methods, the high C₁₈ liquid vegetable oil is combined with a stearic acid source material comprising at least about 84 weight percent of stearic acid, based on the total weight of fatty acids in the stearic acid source. The stearic acid source material is preferably stearic acid which is at least 84 percent by weight stearic acid, and less than 6 weight percent palmitic acid. However, stearic acid esters of low molecular weight monohydric alcohols such as methyl stearate and ethyl stearate may also be utilized. The stearic acid source material may include minor amounts (e.g., 0-10 weight percent) of unsaturated C₁₈ fatty acids of esters, and/or saturated or unsaturated ^c20~^c22 f^attv acids of esters. For cocurrent or batch reactions, the stearic acid component is combined with the vegetable oil in one or more reaction stages to provide a transesterification mixture which may vary in composition depending upon the end product desired, the number of transesterification stages to be utilized, and the degree of equilibrium to be achieved in the transesterification mixture. In general, for both reactions, the weight ratio of stearic acid to triglyceride in the initial transesterification mixture should be at least about 1:3, and preferably at least about 1:1. For single step transesterification mixtures, the weight ratio of stearic acid to triglyceride in the initial transesterification mixture should be at least about 1:2, and preferably in the range of from about 1:1 to about 3:2. A weight ratio of 1.15 parts stearic acid to 1 part soybean oil in a solvent such as hexane is particularly preferred in a single step process. The stearic acid and the triglyceride are desirably dissolved in hexane or other suitable solvent in a weight ratio in the range of from about 0.5 to about 2.0, solvent to combined stearic acid plus triglyceride vegetable oil such as soybean oil.

The transesterification mixture is contacted with the immobilized enzyme under time and temperature conditions for substantially equilibrating the ester groups in the 1-, 3- positions of the glyceride component, with the nonglyceride fatty acid components of the reaction mixture. The reaction time may range from about 0.5 hour to about 100 hours, depending on the concentration and activity of the lipase, and the temperature of the reaction mixture. The reaction temperature may desirably be in the range of from about 35* C. to about 60* C. By "substantially equilibrate" is meant that the transesterification reaction is at least 50 percent complete, and preferably at least 90 percent complete. Lower equilibrium transesterification conditions (e.g., 50-90% equilibrated) may be utilized to increase the reaction speed and or reduce the amount of enzyme used, but this increases the stearic acid required and increases the separation step processing requirements.

There is generally an increase in the diglyceride content of the transesterification mixture as a result of excess water in the reaction mixture. The free fatty acid or fatty acid monoester components, which include a mixture of unsaturated fatty acids together with stearic acid, are then separated from the glyceride components. The fatty acid components are subsequently fully hydrogenated to provide a stearic acid source material for blending with the liquid vegetable oil for subsequent, recyclic utilization in the transesterification reaction.

Illustrated in FIGURE 1 is a flow chart illustrating an embodiment of a batch or continuous cocurrent manufacturing method for preparing a firm-bodied margarine oil in accordance with the present invention. In the illustrated embodiment, a liquid vegetable oil 102, which is bleached and deodorized soybean oil, is combined with stearic acid 104 which is at least 94 percent by weight stearic acid, and hexane 106, in a weight ratio of 1:1.15:4 to form a transesterification mixture. The transesterification mixture may desirably be blended before introduction into the reactor 10, by proportional pump metering. The water 105 may be introduced into the soybean oil 102 at a desired level to maintain enzyme activity at a desired level (e.g., saturated or slightly supersaturated with water) and accommodate and control diglyceride formation in the transesterification reaction. The water 105 may desirably be introduced by conducting the transesterification mixture of soybean oil, hexane and stearic acid through an anionic resin bed or column in which the anionic exchange resin is water-saturated at a temperature of 40-55* C. The soybean oil, stearic acid, hexane and water are introduced into enzymatic transesterification reactor 110 at a temperature in the range of 35 to 75* C., and preferably about 40-50* C. The esterification reactor 110 contains an immobilized 1-, 3- positionally specific transesterification lipase, such as the 1-, 3- positionally specific lipase from Mucor miehei on a suitable substrate (e.g., Novo 3A Lipase as described in Example 1) .

It is important to carry out the transesterifi¬ cation reaction under inert gas in a substantially oxygen-free environment in order to prevent oxidation or rearrangement of linoleic and linolenic acid components which are more vulnerable to such oxidation in unrestricted condition. The oil may be vacuum degassed prior to reaction and maintained under oxygen-free nitrogen if desired.

Such transesterification reactions are conventionally batch or continuous cocurrent flow reactions which reach or approach equilibrium as a function of the concentration of components in the mixture. Separation of the fatty acid components from the transesterification mixture is typically a necessary step of such transesterification procedures.

In this regard, as shown in FIGURE 1, the transesterified reaction mixture which has been transesterified in reactor 110 is conducted to crystallization separator 112. A portion of the hexane may be removed by evaporation prior to introduction into the separator 112 if desired. In the separator, the saturated fatty acid components are precipitated out of solution by reducing the temperature and collecting the precipitate. The saturated fatty acid components, primarily unesterified stearic acid and a small amount of palmitic acid largely derived from the soybean oil 102, is selectively precipitated at temperatures in the range of from -20* C. to about 25* C.

The reaction mixture may be seeded with stearic acid and palmitic acid crystals to facilitate precipitation in the separator 112. The precipitated saturated fatty acids 120 may be separated from the remaining transesterified glyceride reaction mixture in an appropriate manner, such as by filtration or centrifugation. The separated fatty acid crystals may be washed with a cold solvent for triglycerides, such as hexane, to remove any liquid glyceride components entrapped with the saturated fatty acids 120. The glyceride stream 122 from the separator 112 comprises the transesterified glyceride component, the unsaturated fatty acids displaced from the soybean oil 102 upon transesterification, which are not precipitated in crystallization separator 112, and the remaining saturated fatty acids which had not previously crystallized together with at least a portion of the hexane solvent. The solvent may be removed by evaporation and returned to the solvent storage vessel for regular use. The glyceride stream 122 is conducted to a vacuum distillation apparatus 124, for removal of the remaining fatty acids and any hexane present in the mixture. The distillation may be a conventional steam deodorizer distillation apparatus at a temperature of 204 to 274* C. at a vacuum of 1.0 to 25 mm of mercury. The vacuum distillation will be carried out in accordance with conventional steam stripping practice to reduce the fatty acid content to less than 0.10 weight percent, and preferably less than 0.05 weight percent, to provide a margarine oil product stream 126, and a fatty acid distillate stream 128. ' The fatty acid stream 128 is predominantly C₁₈ unsaturated acids derived from the original soybean oil 102. Stearic and palmitic acids may be present in this stream. The palmitoleic and other intermediate chain unsaturated fatty acids constitute less than 0.2 weight percent of the unsaturated fatty acid stream 128. The unsaturated fatty acid stream 128 is introduced into hydrogenator 130 (which may be of conventional design) , where the unsaturated fatty acids are fully hydrogenated to provide a stearic acid stream 132. The stearic acid streams 120, 132 may be subjected to fractional distillation in distillation apparatus 134 to separate intermediate chain fatty acids 138 having less than 18 carbon atoms, and to provide purified stearic acid streams 136 for introduction into stearic acid source vessel 104. The lower molecular weight saturated fatty acids may be readily distilled off under vacuum conditions without damage to the saturated stearic acid. The margarine oil 126 may be provided which has a desirable, broad solid fat index, a smooth mouthfeel, a trans- acid content of less than 6 weight percent, and an intermediate saturated fatty acid content of less than 6 weight percent. While crystallization and distillation techniques are described in the embodiment of FIGURE 1 for component separation, supercritical or subcritical inert fluids such as supercritical carbon dioxide, supercritical hydrocarbons such as propane, or fluorocarbons or such subcritical pressurized liquids near the critical temperature may be used to selectively dissolve, precipitate or otherwise separate fatty acids, triglycerides and other edible fat and oil components to provide low trans- acid, low intermediate chain fatty acid margarine oils. While the system of FIGURE 1 is a batch or cocurrent reaction system, countercurrent transesterification methods may also be used to provide enzymatically transesterified margarine oils. Countercurrent reaction systems may provide higher efficiency and effective component separation.

Because of the mutual solubility of the triglyceride and fatty acid or fatty acid monoester reaction components, countercurrent processes utilizing countercurrent supercritical fluids which selectively extract and transport the fatty acid may desirably be utilized to provide efficient transesterification of the recycled stearic acid components. Countercurrent transesterification procedures may not only provide the reaction efficiencies of countercurrent operation, but also may facilitate separation of reaction products.

In supercritical fluids such as supercritical carbon dioxide, solubility of fatty acid esters such as fatty acid methyl and ethyl esters are typically an inverse function of molecular weight of the fatty acid monoester under various conditions. Similarly, the solubility of fatty acids is inversely proportional to molecular weight of the fatty acid, although fatty acids are typically less soluble in supercritical carbon dioxide, than corresponding fatty acid lower alkyl monoesters of corresponding molecular weight because of the associative or hydrogen bonding characteristics of the fatty acids.

The respective solubilities of fatty acids, fatty acid esters and triglycerides in carbon dioxide is also a function of temperature and partial pressure of C0 at relatively low supercritical pressures, above the critical pressure for C0₂ of about 72.8 atmospheres (at critical temperature of 31.1* C).

An embodiment of continuous transesterification process which moves a fatty acid or fatty acid monoester component countercurrent to triglyceride flow, and which also removes such fatty acid transesterification reaction components from the transesterified glyceride, is illustrated in FIGURE 2.

The high C₁₈ vegetable oil to be trans¬ esterified, which in the illustrated embodiment is soybean oil 212, is saturated with water and introduced into the high pressure column 214 at a point 224 between the upper outlet 216 and the lower stearic acid source material inlet 222. The soybean oil may be conducted through a column containing a water-saturated anionic exchange resin to remove non-triglyceride impurities which might poison the enzyme, and condition the oil for the reaction. The rate of introduction of the soybean oil 212 corresponds to the transesterification reaction rate permitted by the activity of the immobilized enzyme in the column 214. In this regard, the column is packed with an immobilized lipase enzyme, which is immobilized on organic or inorganic, high surface area supports such as porous ceramic rings or pellets, organic supports such as crosslinked ion exchange or phenolic resins which are insoluble in the supercritical fluid, or diatomaceous earth (e.g., Celite) . The surface area of the column packing is very large in order to promote interesterification reaction (e.g., more than 750 square meters of surface area per cubic meter) , and to promote equilibrium dissolution of the low molecular weight components in the supercritical fluid.

Stearic acid or preferably a lower alkyl stearic acid monoester 220, such as a methyl or ethyl ester of stearic acid (e.g., ethyl stearate), which is desired to be transesterified with the triglyceride 212, which may be saturated with water is introduced into the column 214 at a point 222 between the point 224 of introduction of triglyceride, and the lower outlet 218 at a rate which maximizes the desired transesterification reaction. Because this transesterification reaction is conducted in a countercurrent manner, a lower ratio of stearic acid source material components to soybean oil may be used. Lower alkyl monoesters of the stearic acid source material are preferred because they have higher solubility in the supercritical gas.

In operation, supercritical carbon dioxide (or another supercritical fluid such as an ethane-propane mixture or a fluorocarbon gas having a critical temperature for example in the range of from about 30* C. to about 80* C), is introduced at the bottom of the column 214 under pressure and temperature conditions at which relatively low molecular weight fatty acids or fatty acid esters such as stearic acid and ethyl stearate are significantly dissolved, but at which the high molecular weight triglycerides are relatively not substantially dissolved. For example, carbon dioxide pressures in the range of from about 1100 psi to about 4500 (e.g., 2000-3000 psia for ethyl stearate use) , at a reaction temperature in the range of, for example, from about 30* C. to about 40* C, are particularly preferred to provide relatively high fatty acid and/or fatty acid monoester solubility, while providing relatively low triglyceride solubility in the upwardly moving supercritical carbon dioxide stream. Such conditions of pressure and temperature may be provided in which the density of the supercritical gas is less than that of the triglyceride components, so that countercurrent flow is readily achieved. The supercritcal fluid may contain a small amount of water vapor to maintain the catalyst and to facilitate fatty acid solubility in the supercritical gas phase. The temperature, of course, cannot exceed the operating temperature of the enzyme, which will be damaged at high temperatures. In this regard, at lower supercritical pressures, the solubility of the fatty esters and triglycerides is higher at lower temperatures, and a temperature should be selected (e.g., 35* - 55* C.) which maximizes throughput rate for countercurrent transport of the fatty monoester, and the transesterification reaction rate which is necessary to achieve transesterification of the triglyceride and the fatty acid or fatty acid monoester. Fatty acid monoesters, such as methyl and ethyl stearate and the transesterified reaction product monoesters are substantially more soluble in the supercritical fluid than the corresponding acids, and accordingly are preferred reactants. The supercritical gas also serves as a diluent of the triglyceride phase to increase the reaction rate.

The supercritical carbon dioxide gas phase is less dense than the downwardly moving liquid soybean oil stream at pressures used in the system of FIGURE 2 (e.g., 1500-3500 psia) , and the density difference provides the countercurrent flow in the system. The pressure, temperature, column distances and flow rates of fatty acid or fatty acid monoester and carbon dioxide are selected so that in the zone 228 between the point of introduction of the carbon dioxide and the point 222 of introduction of the stearic acid or monoester, the fatty acid or fatty acid monoester is progressively dissolved from the triglyceride into the upwardly moving supercritical C0₂ stream. The zone 224 is primarily a stripping zone in which the fatty acid and/or fatty acid monoester components are removed from the transesterified oil product. The fatty acid or fatty acid monoester components (including the transesterified components) may be substantially completely removed from the triglyceride stream 226 before it is discharged from the column at outlet 218. In this regard, the weight ratio of the flow rate of the carbon dioxide to the flow rate of the stearic acid component 220 introduced in the column 214 may desirably be selected to be in the range of from about 5:1 to about 50:1, under conditions to maximize solubility of the fatty acid or preferably fatty acid monoester component while minimizing the solubility of the triglyceride component phase. In the zone 224, during the time of transit of the soybean oil (e.g., .25 - 6 hours) , the stearic acid monoester 220 undergoes transesterification with the triglyceride component. Because the flow of triglyceride and stearic acid or monoester is effectively diminishingly cocurrent in this stripping zone, the enzymatic transesterification reaction will tend to approach the equilibrium condition of the fatty acid monoester-triglyceride blend at the point 222 of introduction of the monoester. Accordingly, the composition of the fatty acid or fatty acid monoester which enters the countercurrent transesterification zone 226 from the monoester stripping zone 224 will be different from the composition of the fatty acid or monoester 220 introduced into the column 214 at least in part because of the transesterification which occurs in the stripping zone 224. The transesterified triglyceride margarine oil product, which may have substantially all fatty acid and fatty acid monoester components removed therefrom, is withdrawn from outlet 218.

The weight ratio of triglyceride components to the stearic acid or monoester component to achieve a desired degree of transesterification of the triglyceride is substantially greater in the system of FIGURE 2 than the ratio of triglyceride to fatty monoester utilized to achieve an equivalent degree of transesterification in a one or two step batch reaction. In this regard, the stearic acid or stearic acid monoester is introduced into the bottom of the column at a rate compared to the rate of introduction of soybean oil which nay, for example, be about half the proportion used in a batch reaction (e.g., 1:3 to 1:1 weight ratio of stearic acid component to soybean oil) .

The fatty acid or monoester component is dissolved in the upwardly moving C0₂ gas stream and carried into the transesterification zone 226, where it tends toward approaching equilibrium through exchange with the composition of fatty acids or monoesters in the countercurrent oil flow, while this composition is also being changed, through the action of the immobilized enzyme in the column. Accordingly, the fatty acid or monoester component dissolved in the supercritical gas is effectively transesterified in a countercurrent manner with the liquid triglyceride stream as it is conducted from its point of introduction 224 to the point 220 of introduction of the fatty acid monoester.

The triglyceride phase mixture continuously undergoes transesterification reaction as it moves downwardly in the zone 226 containing lipase enzyme countercurrent to the flow of supercritical gas, such that the mixture has an increasing concentration of the desired triglyceride components as it moves down the column. There is also an increasing concentration of transesterified fatty acid or monoester having fatty acid or monoester components derived from the triglyceride in the upwardly moving supercritical gas stream, in the direction toward the point of introduction of the triglyceride. Water vapor may be included in the carbon dioxide flow, the fatty acid ester flow and/or the triglyceride flow to accommodate the transesterification reaction, which may exceed the solubility of water in the triglyceride component, and to produce a desired level of diglycerides, if desired. Fatty acid components produced by hydrolysis reactions in the column 214 may also be removed by the supercritical carbon dioxide flow.

The transesterified fatty monoester dissolved in the supercritical C0₂ gas stream is carried from the column at outlet 216, through pressure let-down valve 230 into separation tank 232, where dissolved fatty acid monoester is taken out of supercritical solution as a result of the pressure reduction. The tank 232 may alternatively be heated to further reduce the solubility of the fatty acid monoester. The solubility reduction may also be accomplished by a combination of a limited pressure reduction (e.g., by 500-1000 psi) and a temperature increase (e.g., to 70-100* C.) so that the work to recompress the C0₂ for recycle use may be reduced. Alternatively, and preferably, the pressure letdown system will desirably be an energy recovery system, such as a piston or turbine engine in which the pressure let-down work is recovered and dissolved components are collected in the recovery system, so that the pressure let-down energy may be at least partially recovered for reco pression of the carbon dioxide upon recyclic operation.

The carbon dioxide which is separated from the fatty acid or monoester is conducted to compressor/thermal conditioner 234 where it is recompressed and reintroduced at the preselected operating temperature as previously discussed. A heat-pump 236 may be used to transfer heat between the compressor 234 and the separator 232 and/or pressure let-down valve 230. If an energy recovery system is used, the pressure let-down piston or turbine motor will desirably be on the same or a directly connected shaft as the compressor. The flow rate of supercritical carbon dioxide (or other supercritical gas solvent) through the column 214 is correlated with the flow rate of fatty acid ester 220 so that it is adequate to dissolve substantially all of the fatty acid monoester under the operating conditions, but dissolves a minimal amount of the initial soybean oil and other triglyceride components. The solubility of the fatty acid or fatty monoester components will desirably be greater than 1 weight percent, and preferably greater than 2 weight percent, while the solubility of triglycerides will be less than 0.5 weight percent and preferably less than 0.25 weight percent in the carbon dioxide gas phase.

If desired, the transesterified fatty ester collected in the separator tank 232 is conducted to a hydrogenation reactor 240 to fully hydrogenate the unsaturated fatty acid components to provide a predominantly stearic acid fatty monoester for reintroduction into the column 214 at point 222, as shown in FIGURE 2. The hydrogenated fatty acid components may be distilled to remove C12-C16 fatty acids, and may be esterified with a lower alkyl monohydric alcohol such as ethanol prior to or subsequent to such distillation. Intermediate chain fatty acid components may be selectively fractionated from the recycle mixture after hydrogenation. While the system of FIGURE 2 utilizes supercritical gas, such a countercurrent method may also utilize a subcritical liquified gas such as propane, propane/ethane mixtures, and liquified fluorocarbon gases (safe and inert) having a critical point of e.g., 30* C. - 90* C. Such systems, at temperatures near (e.g., within 20* C.) of the control temperature exhibit selective solubility of fatty acids and monoesters in 2-phase systems, and generally may be used as described in a manner similar to that of FIGURE 2 at elevated pressures sufficient to maintain the subcritical solvents in the liquid state. The countercurrent system of FIGURE 2 may also be used for a wide variety of transesterification reactions in addition to those which produce the margarine oils of the present disclosure.

Having generally described various aspects of the present invention, the invention will now be more specifically described by the following specific examples.

Exampl 1

Soybean oil (SBO) was converted into a stick margarine oil product which has a similar solid fat index/melting temperature profile to that of a conventional stick margarine oil product, and a smooth organoleptic characteristic. This was done by interesterifying soybean oil with stearic acid, in a two step process, using Novo 3A Lipase, a Mucor miehei immobilized lipase, which is 1-, 3- positionally specific, supplied by NOVO Laboratories, Inc., such as described in European Patent 0140542. The fatty acid distribution of the five major fatty acids of the starting soybean oil was as follows:

Table 1

Weight Percent att o

Palmitic (P) Stearic (S) Oleic (0) Linoleic (L) Linolenic (Ln)

In a first step, 73 grams of a commercial stearic acid product which was 94.0% stearic acid and 4.2 weight percent palmitic acid (Aldrich) was mixed with 157.2 grams of the liquid soybean oil, calculated to provide a final stearic acid concentration of 28.9 weight percent, equivalent to 43.4 weight percent stearic acid in the 1+3 positions.

The reaction was carried out in a hexane solvent system and utilized 0.625 grams of Novo lipase (containing 3.0-11.0 weight percent of water) per gram of oil. The reaction mixture was incubated at 40* C. in a stirred reaction vessel at 250 rp for 48 hours to assure full equilibration. To stop the reaction, the lipase was removed via filtration and the hexane solvent distilled off. The free fatty acids were removed by distillation at less than 1.0mm Hg at a temperature of 500* F. A second reaction was subsequently carried out in the same manner using the transesterified, distilled oil from the first step reaction, using the same stoichiometry, calculated to give a second step reaction product having final theoretical stearic acid concentration of about 45 weight percent.

The following table shows the Fatty Acid Distribution (FAD) in weight percents of the respective first and second step products and the Solid Fat Index (SFI) of the second step product after hexane fractionation compared to a conventional stick margarine oil: able 2

FAD 1st Step 2nd Step Product Product

5.7

^■33m . i lT I* *

12.7

33.1

4.2 tv

Conventional St ck Ma e

Further enzymatic interesterification reactions between soybean oil and stearic acid were carried out as described in Example 1. Samples were withdrawn periodically and analyzed by HPLC. A rapid HPLC analysis for triglycerides was implemented. The HPLC conditions are summarized below: Column: C-18 (Alltech) Adsorbosphere 4.6 x 250mm,

5 micron Mobile Phase: 70:30 Acetone-Acetonitrile Flow Rate: 2mL/min. Temperature: 40* C Detector: Refractive Index (Waters 401)

A chromatogram of a sample of soybean oil is illustrated in FIGURE 3. The respective component peaks are identified by their respective retention times, in minutes. The corresponding weight percents of the components as shown in FIGURE 3 are as follows:

Table 3

Peak Retention Weight

Compound Time Percent

T.T.T.n 4.83 9.8

LLL 5.51 25.2

OLL 6.53 14.3 PLL 6.73 16.4

OOL 7.91 7.5

PLO 8.14 14.0

POO 9.93 10.3

SLS 12.20 2.6

Triglycerides in soybean oil were identified, along with product TAGs from an interesterification reaction of soybean oil with stearic acid, through the use of standard oils with known TAG composition. Mixed standards were also produced by the interesterification of standard TAGs, such as LLL, with stearic and palmitic acids. When most of the significant TAGs were identified and their retention times on the HPLC column were noted, data on the enzyme reaction was gathered. FIGURE 4 is an HPLC chromatogra of soybean oil which has been transesterified with stearic acid. As in FIGURE 3, the respective component peaks are identified by their respective retention times. The corresponding weight percentages of the components, as shown in FIGURE 4 are as follows:

Table 4

Peak Retention Weight

Compound Time Percent

Unknown 3.47 5.5 LLn 4.84 2.3

LLL 5.59 6.8

OLL 6.63 3.3

PLL 6.89 6.6

SLL 8.05 21.4

SLO 9.78 11.5

SLP 10.22 9.5

Unknown 11.33 .23

SLS 12.19 26.4

SOS 15.32 7.8

Unknown 18.84 .48

By quantitatively following the disappearance of certain TAGs, such as LLL, from the initial soybean oil, or the production of certain TAGs, such as SLL or SLS, classical kinetic data was obtained and used to design a single step reaction using an increased level of transesterification enzyme, and a reduction in reaction time from 96 to 6 hours, as described in the following example.

Example 3

A single step reaction using increased levels of enzyme, was carried out having a decreased reaction time of 6 hours. The downstream separation processing of the interesterified oil was aided out by fractional crystallization of the free fatty acids from the reaction mixture. This also increased product yield.

To provide the desired composition, 180 grams of stearic acid reagent was added to 157.2 grams soybean oil.

The reaction was set up in a hexane solvent system which consisted of 2.5 ml hexane per gram of reactants. For this example, 0.375 grams of Novo 3A Lipase product (a Mucor miehei immobilized 1-, 3- specific lipase) was used per gram of oil.

The reaction was incubated for 6 hours at 40' c. in a stirred reaction vessel at 250 rpm.

A large excess of stearic acid was utilized in this batch mode reaction to achieve the desired degree of substitution of stearic acid in the triglyceride end product. In order to improve the economics of the process, and to prevent the formation of undesirable trisaturates during subsequent distillation or deodorization procedures, the excess stearic acid should be removed and recovered from the reaction mixture, prior to high temperature treatment. This was done by selective crystallization of the stearic acid from the reaction mixture. To accomplish this, the mixture was filtered to remove the enzyme, which was then washed with hexane to remove any absorbed fat. The washings and filtrate were combined and concentrated to about 70 percent of the original reaction volume. The concentrated solution was allowed to stand for 8 hours at 20* C, then at 4^* C. for 16 hours, which produced a crystalline precipitate of saturated fatty acid. The large crystalline mass was broken up, slurried with cold hexane and vacuum filtered. The crystals were washed a total of four times, with an equal volume of cold hexane each time, to remove fat. The combined washings were distilled to remove hexane and the fat was then subjected to deodorization. The crystals were then dried under vacuum and analyzed. The FAD and glyceride analyses of the crystals are shown in Tables 5 and 6.

Table 5 FAD Analysis of Recovered Fatty Acid Crystals

<0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

3.7 <0.1

0.9 <0.1 92.2

0.8 <0.1

1.4

0.2

0.2 <0.1 <0.1

0.2 <0.1 <0.1 <0.1

0.1

Table 6 Analysis of Recovered Fatty Acid Crystals

Triglyceride

Fatty Mono- Digly- Carbon Number (total) Acid glvcerides cerides 48 50 52 54 56 58

94.3 0.1 2.9 — 1.0 1.7 — The overall recovery of stearic acid in the crystallization step, accounting for exchange, was 88.7% of the theoretical value.

The reaction product was processed in a manner similar to that of the two step process of Example 1. The fatty acid distribution and solid fat indices, respectively, of the reaction product as compared to a conventional stick margarine oil, were as follows:

Table 7 Fatty Acid Distribution

FAD One Step Conventional

Product t c Ma ne O

33.2

SFI

* c.

10.0 21.1 26.7 33.3 37.8

To test the feasibility of reusing the recovered stearic acid in subsequent reactions, a test was set up in which recovered stearic acid was used for a one stage transesterification reaction as described hereinabove. Analyses of this particular batch of stearic acid crystals indicated that the material was 86.5 weight percent free fatty acids, of which 89.9 weight percent was stearic acid, and approximately 10.1 weight percent of mono, di and triglycerides. The amount of stearic acid added to the reaction mixture was adjusted to account for the amount of stearic acid present in the recycled acid. SFI, FAD and glyceride analyses on the transesterified product indicate that it is essentially the same as control batches. These results can be seen in Tables 9 through 11.

Table 9

SFI Analysis of Transesterified Soybean

Oil Produced Using Recovered Stearic Acid

W t ercent solids Temperature

10.0' C.

10.0* C.

21.I' C.

21.1* C.

26.7* C.

33.3* C.

37.8* C.

37.8^* C.

* (Values are slightly high due to SSS formed during deodorization)

Table 10

FAD Analysis of Transesterified Soybean

Oil Produced Using Recovered Stearic Acid

Table 11

Glyceride Analysis of Transesterified

Soybean Oil Produced Using Recovered Stearic Acid

Triglyceride Fatty Mono- Digly- Carbon Number

Acid glvcerides cerides 48 50 52 54 56 58

<0.1 <0.1 8.8 0.1 1.4 11.7 76.9 <0.1 0.4

Example 4

In order to make margarine, a ten liter reaction flask, and a temperature-controlled water bath were used to prepare a batch of transesterified margarine oil generally as previously described in Example 3. In accordance with such reaction, 700 grams of soybean oil, 800 grams of stearic acid, 262 grams of the NOVO 3A immobilized Lipase enzyme product and 3.75 liters of hexane were reacted to substantial equilibrium in the reaction flask. This provided a 15-fold scale up and enough transesterified oil for two batches of margarine. Analyses indicated that the fat produced in the large scale batch was substantially identical to the small scale preparations described in Example 3.

The transesterified soybean oil, which had an SFI profile substantially equivalent to that of conventional stick margarine, was incorporated into both stick margarine oil and tub margarine oil formulas. These were prepared on a small scale (350 grams) , in a jacketed, cooled Waring blender. The transesterified soybean oil, when incorporated into the tub margarine oil formula, demonstrated harder physical properties than the control. When transesterified soybean oil was incorporated into the stick margarine oil formula, the physical properties were similar to that of the stick margarine oil control.

The removal of free fatty acids from the interesterification reaction mixture was done by vacuum steam distillation (deodorization) . The conditions of the distillation and also the concentration of free fatty acids in the reaction mixture were factors which were investigated to determine if they produced changes in the final product, both physically and chemically.

Table 12 shows the effect of free stearic acid concentration, in transesterification mixture and also of extended hold times at elevated temperatures (480* F.).

Table 12

At higher stearic acid concentrations, tristearin (SSS) , is produced and increases the melting solids at 37.8* C. This table also shows that at extended hold times, SSS is produced. These results indicate that in the presence of a high concentration of stearic acid (30%) or when the deodorization is held at 480* F. for 1 hour, undesirable non-enzymatic interesterification may occur during deodorization producing high melting tristearin which adversely affects the mouthfeel of the product. It is therefore necessary to remove, in a suitable manner such as via crystallization, the bulk of the stearic acid remaining in the reaction mixture prior to deodorization to avoid formation of undesirable tristearin. Accordingly, in accordance with the present invention, it will be appreciated that improved margarine oils have been provided which have low trans- acid content, together with smooth, organoleptic mouthfeel characteristics and desirable melt characteristics. While the invention has been described with respect to certain specific embodiments, it will be appreciated that various modifications and adaptations will be apparent from the present disclosure, and are intended to be within the scope of the following.claims.

Claims

WHAT IS CLAIMED IS:

1. A margarine oil having both low trans- acid and low intermediate chain fatty acid content, together with a broad margarine type solids fat index melting profile and a smooth organoleptic consistency, comprising a blend of from about 84 to about 95 weight percent fatty acid triglycerides, from about 5 to about 15 weight percent fatty acid diglycerides and less than about one weight percent of fatty acid monoglycerides, based on the total weight of said blend, said margarine oil comprising less than 3 weight percent of esterified trans- unsaturated fatty acid and less than 6 weight percent of intermediate chain saturated fatty acids, from about 25 to about 45 weight percent of esterified linoleic acid, from about 0 to about 11 weight percent of esterified linolenic acid, from about 5 to about 25 weight percent of esterified oleic acid based on the total weight of esterified fatty acids, said margarine oil having a non-random fatty acid distribution in which esterified stearic acid is predominantly distributed in the 1-, 3- positions, while esterified unsaturated fatty acid moieties are in higher concentration at the 2- position of said glycerides within the following ranges:

and said margarine oil having a solid fat content profile within the following ranges:

Dilatometric Solid

Temperature Fat Index Percent

10* C. 7-31

21.1* C. 3-25

26.7* C. 0.75-10

33.3* C. 0.5 - 4

38.7* C. less than 3

2. A margarine oil in accordance with Claim 1 having a firm bodied consistency at refrigeration temperature, and having a solid fat index of from about 23 to about 31 percent at 10* C. , from about 15 to about 25 percent at 21.1* C. , from about 6 to about 10 percent at 26.7* c, from about 0.5 to about 4 percent at 33.3' C. and from about 0 to about 3 percent at 38.7^* C.

3. A margarine oil in accordance with Claim 1 having a soft-bodied consistency at refrigeration temperature, and having a solid fat index of from about 7 to about 12 percent at 10* C. , from about 3 to about 10 percent at 21.1* C, from about 0.75 to about 8 percent at 26.7* C. , from about 0.5 to about 3 percent at 33.3* C, and from about 0 to about 1.5 percent at 38.7* C.

4. An enzymatic transesterification method for preparing a margarine oil in accordance with Claim 1, comprising the steps of providing a stearic acid source material selected from the group consisting of stearic acid, stearic acid monoesters of low molecular weight monohydric alcohols, and mixtures thereof, said stearic acid source material comprising at least about 84 weight percent of stearic acid, based on the total weight of fatty acids in said stearic acid source material, providing an edible liquid vegetable oil comprising at least about 80 weight percent of esterified eighteen carbon fatty acid moieties based on the total weight of the edible liquid vegetable oil triglyceride, said vegetable oil further comprising less than 7 weight percent of esterified palmitic acid in 2- glyceride position, and less than 4 weight percent of esterified stearic acid in the 2- glyceride position, at least about 20 weight percent of esterified oleic acid in each of the 1, 2 and 3 glyceride positions, at least about 20 weight percent of esterified linoleic acid, at least about 5 weight percent of esterified linolenic acid, and less than 2 weight percent of esterified stearic acid in the 2- position, transesterifying said stearic acid source material and said vegetable oil triglyceride of a 1-, 3- positionally specific extracellular lipase transesterification enzyme, at a weight ratio of stearic acid source material to triglyceride oil in the range of from about 0.5:1 to about 2:1 to substantially equilibrate the ester groups in the 1-, 3- positions of the glyceride component with the nonglyceride fatty acid components of the reaction mixture, separating the transesterified free fatty acid components from the glyceride components of the transesterification mixture to provide a transesterified margarine oil product and a fatty acid mixture comprising fatty acids, fatty acid monoesters or mixtures thereof released from said vegetable oil, and hydrogenating the fatty acid mixture to provide a stearic acid source material for recyclic reaction with said vegetable oil triglyceride.

5. A method in accordance with Claim 4 wherein intermediate chain fatty acids are at least partially removed from said hydrogenated fatty acid source by distillation to provide a recycle stearic acid source material having less than 6 weight percent intermediate chain saturated fatty acids.

6. A countercurrent method for preparing a transesterified oil comprising the steps of providing a transesterification reaction zone containing a 1-, 3- positionally specific lipase transesterification enzyme, introducing a vegetable oil into the transesterification reaction zone to provide a triglyceride reaction stream through the reaction zone. introducing a fatty acid source material selected from the group consisting of fatty acid, fatty acid lower alkyl monoesters and mixtures thereof into the transesterification reaction zone to provide a fatty acid or fatty acid monoester reaction stream, conducting a supercritical gas or subcritical liquified gas countercurrent fluid which preferentially dissolves fatty acids and fatty acid monoesters over triglycerides under two-phase conditions through said zone countercurrent to the flow of the triglyceride reaction stream, at a rate and under pressure and temperature conditions to maintain a separate phase of said countercurrent fluid containing fatty acid or fatty acid monoester through the reaction zone in intimate contact with the triglyceride reaction stream, carrying out transesterification reaction of the triglyceride stream with the fatty acid or fatty acid monoester stream in the reaction zone, withdrawing a transesterified triglyceride margarine oil stream which has been transesterified with the stearic acid source material from the reaction zone, withdrawing a countercurrent fluid phase from said reaction zone countercurrent to the margarine oil stream having dissolved therein transesterified free fatty acids or fatty acid monoester produced by transesterification of said stearic acid source material with said vegetable oil, hydrogenating said transesterified fatty acid or fatty acid monoester to provide a recycle stearic acid source material, and introducing said hydrogenated recycle source material into said reaction zone.

7. A method in accordance with Claim 6 wherein said transesterified oil is a transesterified margarine oil, wherein said vegetable oil is soybean oil, and wherein said fatty acid source material is selected from the group consisting of stearic acid, stearic acid lower alkyl monoesters and mixtures thereof comprising at least 94 weight percent stearic acid in free or monoesterified form.

8. A method in accordance with Claim 7 wherein said countercurrent fluid is supercritical carbon dioxide gas at a pressure in the range of from 1100 to 2500 psia at a transesterification reaction temperature in the range of from about 40 to about 70^* C.

9. A method in accordance with Claim 7 wherein said countercurrent fluid is subcritical liquified ethane, propane, fluorocarbon gas or mixtures thereof, having a critical temperature below 100* C. which exhibits triglyceride phase separation at reaction temperature conditions approaching the critical temperature.