Dilatometric properties of some glycerides of confectionery fats

Two triglycerides, 1-oleodisterain and 2-palmito-oleostearin, which are components of some confectionery fats, were synthesized and their melting behavior and dilatometric properties were determined. Expansivities and melting dilations of the various polymorphic forms were measured. 1-Oleodisterain was found to have two melting points, 30.3 and 42.1°C., while 2-palmito-oleostearin was found to have melting points at 24, 37, and 40.5°C. The rate of transformation of the thermodynamically unstable polymorphs at temperatures below their melting points were much more rapid than those for the corresponding 2-oleo isomers previously reported. Mixtures of 2-oleopalmitostearin with 2-palmito-oleostearin and 1-oleodistearin with 2-oleodistearin were examined dilatometrically. In each of these mixtures the components apparently do not temper at the same rate to similar polymorphic forms and thus there is some degree of incompatibility even though in each of these mixtures the components are positional isomers. The properties of the intermediate melting mixtures are dependent on the method of tempering. Presented at the 52nd Annual Meeting of the American Oil Chemists' Society, St. Louis, Missouri, May 1–3, 1961. One of the laboratories of the Southern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

Dilatometric investigations of fats II. Dilatometric behavior of some plastic fats between 0° C. and their melting points

Summary 1. Dilatometric curves between 0°C. and their melting points have been obtained for the following fats: lard, butterfat, cottonseed oil, peanut oil, a commercial margarine oil, a commercial all-hydrogenated vegetable shortening, three samples of soybean oil hydrogenated to different degrees, a hard butter fractionally crystallized from hydrogenated peanut oil, a mixture of tristearin and soybean oil, and a synthetic fat containing equal molar proportions of stearic and oleic acids. 2. The dilatometric curves, of volume change in the fat against temperature, were in every case composed of a series of straight lines, separated by sharp breaks or transition points. 3. The number of linear sections in the dilatometric curves corresponded in a general way with the known degree of complexity in the glycerides of the fats, and varied from two in the case of the relatively simple stearic-oleic glyceride mixture, to at least seven in the case of the all-hydrogenated shortening. Since each break in the curve must correspond to the disappearance of a distinct class of solid glycerides or glyceride complexes, the application of dilatometry to the qualitative and quantitative determination of glyceride composition in fats is suggested. 4. Only two of the fats examined, the mixture of tristearin and soybean oil, and the synthetic stearicoleic glyceride mixture, exhibited polymorphism, even after rapid solidification in ice water. Presented before the American Oil Chemists’ Society Meeting, New Orleans, Louisiana, May 10 to 12, 1944. This is one of four regional research laboratories operated by the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Physical properties of aceto- and butyro-oleins,mono-olein,and diolein

1. A series of six oleoglycerides: 1,2-diaceto-3-olein, 1,2-dibutyro-3-olein, 1-aceto-3-olein, 1-butyro-3-olein, 1,3-diolein, and 1-mono-olein, was prepared and purified, and some of their physical properties were determined.
2. Data on densities and refractive indices of the compounds revealed that substitution of short-chain acyl groups for one or both of the hydroxyl groups in 1-mono-olein increases the density and decreases the refractive index. The effect is more pronounced for the aceto than the butyro groups.
3. By the capillary tube method, melting- and transition-point data were determined for each glyceride. For the triglycerides, 1,2-diaceto-3-olein and 1,2-dibutyro-3-olein, one melting point and two transition points for each were found. For the diglycerides, 1-aceto-3-olein and 1-butyro-3-olein, two melting points and two transition points for each were found. Two melting points and one transition point each for 1,3-diolein and 1-mono-olein were found. These melting and transition points were substantiated by heating-curve data.
4. Where possible, dilatometric measurements were made for the various polymorphic forms of the glycerides. From the data were calculated expansibilities in the solid and liquid states, melting dilations or volume changes accompanying transformations, and dilatometric melting points.

     

Thermal properties of 2-Oleodipalmitin and 2-Elaidodipalmitin and some of their mixtures

The polymorphism of 2-oleodipalmitin (POP), 2-elaidodipalmitin (PEP), and five of their mixtures was investigated by differential scanning calorimetry (DSC). The heat of fusion (ΔH_f), heat of crystallization (ΔH_c), and heat of transition (ΔH_t) were determined. Rapid conversion to higher polymorphs, partial melting during conversion, and the overlapping of polymorphic forms precluded accurate determination of some caloric values. Four of five previously identified polymorphs of POP and all four polymorphs of PEP were identified by DSC. Five POP: PEP mixtures containing 8, 16, 25, 50, and 75% PEP, respectively, were examined. The presence of PEP in POP increased the stability of the lower POP polymorphs and, in concentrations as low as 8%, also increased the conversion rate of the higher POP polymorphs. In these heating curves, POP forms 5, 4, and 3, and a higher melting fraction that consisted of higher polymorphs of POP, polymorphs of PEP, and probably mixed crystals were evident. The ΔH_f values for the tempered mixtures are lower, and the ΔH_c values for the mixtures are higher than the calculated values. Heating and cooling curves and calorimetric data tables for POP, PEP, and their five mixtures are included. Presented at the AOCS Meeting in New Orleans, May 1971.     

Properties of 2-oleodipalmitin, 2-elaidodipalmitin and some of their mixtures

The glycerides 2-oleodipalmitin (POP) and 2-elaidodipalmitin (PEP) were synthesized and their melting behavior and dilatometric properties were determined. Three mixtures of POP with PEP were examined. Five polymorphs of POP and four of PEP were identified by x-ray diffraction patterns. Rates of transformation of the lower melting polymorphs were, in general, quite rapid at temperatures just below their melting points. But transformation of unseeded POP to its highest melting form was slow and required several days at a temperature just below melting. Coefficients of expansion were determined for the highest melting polymorph and the liquid form of each triglyceride. Melting dilation was determined for the highest melting polymorph. Mixtures of POP with PEP exhibited different melting ranges depending on the tempering procedures and the composition, but even quickly-solidified mixtures tempered without melting to the highest melting range as they were slowly heated over a period of 2 hr. Slow cooling from the melt essentially segregated the components. Presented at the AOCS Meeting, Minneapolis, October 1969. So. Utiliz. Res. Dev. Div., ARS, USDA.     

Enzymatic interesterification of tallow-sunflower oil mixtures

In an effort to improve the physical and/or thermal characteristics of solid fats, the enzymatic interesterification of tallow and butterfat with high-oleic sunflower oil and soybean oil was investigated. The two simultaneously occurring reactions, interesterification and hydrolysis, were followed by high-performance liquid chromatography of altered glycerides and by gas-liquid chromatography of liberated free fatty acids. The enzymes used in these studies were immobilized lipases that included either a 1,3-acyl-selective lipase or acis-9-C₁₈-selective lipase. The degree of hydrolysis of the fat/oil mixtures was dependent upon the initial water content of the reaction medium. The extent of the interesterification reaction was dependent on the amount of enzyme employed but not on the reaction temperature over the range of 50–70°C. Changes in melting characteristics of the interesterified glyceride mixtures were followed by differential scanning calorimetry of the residual mixed glycerides after removal of free fatty acids. Interesterification of the glyceride mixes with the two types of enzymes allowed for either a decrease or increase in the solid fat content of the initial glyceride mix.     

Dilatometric studies of pure triglycerides and mixtures

Summary The melting dilations and the coefficients of expansion of the solid and liquid states have been reported for five symmetrical mixed triglycerides and three simple triglyceride . The melting dilations were found to decrease with increasing proportions of oleic acid in the triglyceride molecule. In some simple mixtures the melting dilations of the several phases were found to occur discretely, but in the more complex systems there was an extension and overlapping of the melting ranges. In the mixtures of triolein with more saturated triglycerides, the melting point of triolein was found to be generally unaffected, but the melting points of the more saturated glycerides were lowered by the presence of triolein. Calculations of the solid-to-liquid ratios from dilatometric data were found to be impossible in the more complex mixtures due to wide variations in the melting dilations of the several phases and to the overlapping of their melting ranges. Approximate calculations of solid-to-liquid ratios in simple systems in which melting dilations occur discretely can be accomplished if the melting dilations of the individual triglycerides are known. Paper No. 2703 of the Scientific Journal Series. Minnesota Agricultural Experiment Station, and Hormel Institute publication No. 73. Submitted as part of Ph.D. Thesis by B. M. Craig, University of Minnesota, 1950. Presented at meeting of the American Oil Chemists Society, San Francisco, Calif., September, 1950.     

Fractionation of lard and tallow by systematic crystallization

Summary Lard and edible tallow were subjected to a series of fractional crystallizations from acetone at temperatures from 20° to -45°C. Six recrystallized precipitate fractions and a filtrate residue were obtained from each fat. In addition to determining the more common physical and chemical characteristics, fatty acid composition of each fraction was calculated from spectrophotometric data, iodine value, and thiocyanogen value. The consistent results obtained throughout by the spectrophotometric method of fatty acid analysis lend further confirmation to the reliability of this method for composition studies of natural fats. The approximate amounts of tri-saturated, di-saturated, mono-saturated, and tri-unsaturated glycerides of the lard and tallow were estimated from the analysis of each fraction on the assumption that not more than two of these classes of glycerides were present in any one fraction. The tallow contains much higher proportions of tri-saturated and di-saturated glycerides and correspondingly lower proportions of the mono-saturated and tri-unsaturated glycerides than does lard. The amount of tri-unsaturated glycerides in lard was found to be significantly greater than meager information in the literature would indicate. The data indicate that the general pattern of glyceride formation in animals such as the pig and cow is probably of random character. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture. Presented at the 19th fall meeting of the American Oil Chemists’ Society, Chicago, Ill., Nov. 7–9, 1945.     

Dilatometric properties of some butyropalmitins,butyrostearins, and acetopalmitins

1. Six aceto- and butyroglycerides, including di-and triglycerides, were prepared and purified, and a number of their physical properties were determined.
2. Melting and transition points for each of the glycerides were determined by experiments with small portions of the samples in capillary tubes; the “thrust-in” technique was employed to detect some polymorphic transitions occurring in intervals as short as one second.
3. Using the data on melting and transition points, dilatometric data were obtained, insofar as possible, for the various crystalline modifications of the compounds as well as for the liquid state. From the dilatometric data calculations were made for expansibilities in the liquid and various solid states, and melting dilations for several solid states. In one instance the volume change on phase transition, without melting, was calculated.
4. From X-ray diffraction patterns the long and short crystal spacings for the highest melting forms of several of the glycerides were determined. On the basis of the short spacings, polymorphic designations commonly used for fats and oils were assigned. The long spacings obtained indicated a triple chain length structure for some of the compounds and as yet an undetermined structure for the other compounds.

     

Investigation of phase transitions in glyceride/paraffin oil mixtures using ultrasonic velocity measurements

A pulse echo technique has been used to measure the ultrasonic velocity of a number of 15% w/w glyceride/paraffin oil mixtures with increasing temperature (0–70 C). At the lower temperatures the glycerides are completely solid and there is a fairly steady decrease in velocity with temperature (ca. −3.8 ms⁻¹C⁻¹). As the temperature rises the glycerides become increasingly soluble in the paraffin oil and the velocity decreases more rapidly. Once the glyceride is completely soluble in the paraffin oil, a fairly steady decrease in velocity with temperature (ca. −3.3 ms⁻¹C⁻¹) resumes. The dependence of ultrasonic velocity on the amount of solid glyceride present means the technique can be used to investigate phase transitions in binary glyceride/oil mixtures.     

Utilization of high-melting palm stearin in lipase-catalyzed interesterification with liquid oils

Palm stearin with a melting point (m.p.) of 49.8°C was fractionated from acetone to produce a low-melting palm stearin (m.p.=35°C) and a higher-melting palm stearin (HMPS, m.p.=58°C) fraction. HMPS was modified by interesterification with 60% (by weight) of individual liquid oils from sunflower, soybean, and rice bran by means of Mucor miehei lipase. The interesterified products were evaluated for m.p., solid fat content, and carbon number glyceride composition. When HMPS was interesterified individually with sunflower, soybean or rice bran at the 60% level, the m.p. of the interesterified products were 37.5, 38.9, and 39.6°C, respectively. The solid fat content of the interesterified products were 30–35 at 10°C, 17–19 at 20°C, and 6–10 at 30°C, respectively. The carbon number glyceride compositions also changed significantly. C₄₈ and C₅₄ glycerides decreased remarkably with a corresponding increase of the C₅₀ and C₅₂ glycerides. All these interesterified products were suitable for use as trans acid-free and polyunsaturated fatty acid-rich shortening and margarine fat bases.     

Determination of the glyceride structure of fats

A method has been described for the quantitative determination of the following six glyceride types in fats: SSS, SSU, SUS, SUU, USU, and UUU. The method involved a quantitative oxidation of the unsaturated acids in the whole fat to the corresponding dicarboxylic acids. The oxidized fat was separated on a liquid-liquid partition column into two fractions, the first containing glycerides having no dicarboxylic acid or one dicarboxylic acid and the second containing glycerides with two or three dicarboxylic acids. Analysis of these fractions by gas chromatography coupled with lipase hydrolysis allowed the calculation of the proportions of the above six glyceride types. The oxidation, fractionation, lipase hydrolysis, gas chromatographic analysis, and the over-all method were checked on natural fats and mixtures of synthetic glycerides. The final glyceride composition appeared to be reliable to within plus or minus 2 unit per cent. Analyses are given for five natural fats. The compositions found agree very well with those calculated by a distribution theory recently proposed by Vander Wal. Contribution from the National Research Council of Canada, Prairie Regional laboratory, Saskatoon, Saskatchwan. Issued as N.R.C. No. 6161.     

Effect of liquid fat on melting point and polymorphic behavior of cocoa butter and a cocoa butter fraction

The polymorphic behavior of cocoa butter and a high-melting fraction of cocoa butter (CBF) was investigated by differential scanning calorimetry. The effect of liquid fat on melting point and polymorphic behavior was established for six mixtures: 83.5% cocoa butter and 16.5% of a low-melting fraction of cocoa butter (CBF-LM), 90% cocoa butter and 10% olive oil, and four mixtures of CBF and olive oil containing 10%, 20%, 30%, and 50% olive oil. Six polymorphs were found for cocoa butter and at least five for CBF. The melting points for cocoa butter and CBF were 35 and 38 C, respectively. Addition of CBF-LM to cocoa butter reduced the observable polymorphs to four and the melting point to 32.5 C. In cocoa butter, 10% olive oil reduced the observable polymorphs to three and the melting point to 31.5C. Similarly, 10% olive oil in CBF reduced the observable polymorphs to three and the melting point to 37 C. Amounts of 20%, 30%, and 50% olive oil in CBF reduced the polymorphs to two and the final melting point to 34.5, 33, and 32 C, respectively. Possible explanations for the observed polymorphic behavior are advanced. Changes in the rates of tempering of cocoa butter and CBF on addition of various amounts of liquid fat are discussed.     

Dilatometric investigations of fats. VI. Melting dilation as a function of chain length in fatty acids and their glyceryl esters

Melting dilations have been determined for the even-numbered, saturatedn-fatty acids in the series lauric through stearic, and some of their glyceryl esters. These data have been correlated with data obtained previously to determine the relationship between melting dilation and the effective chain length of these compounds. The melting dilations of the mono-, di-, and triglyceryl esters of a fatty acid were found to be proportional to the acid residue content of each compound. The melting dilation of a monoglyceride was one-half that of the diglyceride and one-third that of the triglyceride of the same fatty acid. The increment of melting dilation of the fatty acids and glyceryl esters increased regularly with each addition of two methylene groups, with the end group components exerting a contant effect on the volume change. Equations were developed for calculating the melting dilation of then-fatty acids and their glycerides as a function of chain length of the fatty acid radical. The melting dilations of those compounds which are unsaturated, or have less than 10 carbon atoms, cannot be calculated by these equations.     

Studies on lipid responses to interesterified soya oil-butterfat mixture in hypercholesterolemic rats and human subjects

Interesterified soya-butterfat feeding significantly decreased serum cholesterol in humans and in experimental rats. This decrease was more effective than when simple mixtures of the two fats were fed. Studies with the experimental rat indicate higher rates of side-chain degradation of cholesterol as well as 7-α-hydroxylation of cholesterol when interesterified fats replace a mixed fat regimen. The lowering of serum cholesterol parallels the decrease in concentration of fully saturated glycerides and redistribution of myristic acid from the 2-position in the glyceride to 1- and 3-positions of glycerides following interesterification.     

Thermal properties of fats and oils. VIII. Specific heats,heats of fusion,and entropy of alpha and beta tung oils

Summary Beta tung oil belongs to that group of substances which are capable of existing in more than one crystalline form, each of which has a distinet melting point. Three different melting points of the beta tung oil were observed, each dependent upon the rate of cooling. Forms I, II, and III have been used to distinguish beta tung oil melting at 52.8°, 44°, and 28° C., respectively. Equations were developed to express in cals./g./°C. the specific heats of the stable forms of tung oil. Alpha tung oil Solid state (−184° to −43°C.)C _p =0.404+0.001t Liquid state (9° to 80°C.)C _p =0.463+0.0011t Beta tung oil Solid state (−178° to 27°C.)C _p =0.390+0.0013t Liquid state (67° to 87° C.)C _p =0.489+0.00016t The specific heat of beta tung oil was found to be higher when the sample was rapidly cooled than when it was slowly cooled or tempered. The heat of fusion of the beta form of tung oil was caleulated to be 16.12 cals./g., and for the alpha form to be 21.02 cals./g. Entropies at 298.16°K. were 231.04 and 252.15 entropy units for the two forms of these oils, respectively. The liquid glycerides present at any temperature in the melting range were estimated from the data for the heat contents of the oils. The rate of liquidphase formation at constant heat input of both alpha and beta tung oils, unlike that of cottonseed and peanut oils, increased sharply during the final 10° of the interval owing to the greater homogeneity of the glycerides of the former. A report of a study made under the Research and Marketing Act of 1946. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration. U. S. Department of Agriculture.     

Polymorphic transformations in sn-1, 3-distearoyl-2-ricinoleyl-glycerol

Polymorphic transformations of sn-1,3-distearoyl-2-ricinoleyl-glycerol (SRS) have been studied with differential scanning calorimetry, X-ray powder diffraction (XRD), synchrotron radiation X-ray diffraction, and Fourier transform infrared spectroscopy (FTIR) techniques by using a 99.8% pure sample. Four polymorphs, α, γ, β′₂, and β′₁, were isolated. The thermal behavior of the four forms showed that the fusion of α at 25.8°C was followed by the crystallization of γ which melts at 40.6°C, and β′₂ and β′₁ revealed melting peaks at 44.3 and 48.0°C, respectively. No β form was observed, even when the two β′ forms were annealed around their melting points over one week. The XRD long spacing indicates that α packs into a double chain-length structure; however, γ and the two β′ phases pack into a triple chain-length structure. The polarized and nonpolarized FTIR spectra in methylene scissoring and methylene rocking regions indicated a parallel subcell packing in γ, and a mixture of orthorhombic perpendicular and parallel or hexagonal subcells in the β′₂ and β′₁ phases. Consequently, SRS exhibits quite a unique polymorphic behavior, compared to tristearoyl glycerol and sn-1,3-distearoyl-2-oleoyl-glycerol.     

Development of edible tallow fractions for specialty fat uses

Edible beef tallow was effectively fractionated by an acetone crystallization procedure to yield five fractions: two solid glyceride fractions comprising 14% (ca. 7% each) of the original tallow; two liquid fractions of 59% and 7%; and one semisolid fraction of 20%. The solid glycerides were composed of ca. 80% saturates (saturated fatty acid glyceride components), approximately an equal mixture of palmitate and stearate, with oleate as the principal unsaturate. The liquid glycerides were composed of more than 65% unsaturates (unsaturated fatty acid glyceride components), predominantly oleate, with the saturates a 3:1 mixture of palmitate and stearate. The semisolid glyceride fraction was similar to cocoa butter. It was one-third unsaturated, mainly oleate with the saturates a mixture of palmitate and stearate. The thermal behavior of the fractions was studied by differential scanning calorimetry. The liquid fraction had a differential scanning calorimetry final melting profile similar to commercial salad oil and the profile of the semisolid fraction resembled that of cocoa butter. The semisolid fraction appeared to be compatible with cocoa butter over a wide range. Mixtures of 5 and 50% cocoa butter with the semisolid fraction had melting profiles similar to that of the original cocoa butter. Presented in part at the AOCS Meeting, Los Angeles, April 1972. ARS, USDA.     

The glyceride structure of camphor(Cinnamomum camphora) seed fat

The glyceride structure of a specimen ofCinnamomum camphora seed fat has been studied using oxidation procedure for determining the trisaturated and the gravime tric azelaogly ceride analysis technique for determining di- and monosaturated glycerides. The fat contains 93% saturated acids and the molecular proportions of tri-, di- and monosaturated and triunsaturated glycerides are found to be 80,17,1 and 2% respectively. The pattern of acyl group distribution is in close agreement with the requirements of Random Distribution, Glyceride Type Distribution Rule, Widest Distribution and the three theories of Gunstone. There is no restriction in synthesis of fully saturated glycerides. The mean position of first double bond in fatty acids suggests the presence of positional isomers. Part of author’s Ph.D. thesis, Agra University, 1969.     

Crystallization and transformation mechanisms of α, β- and γ-polymorphs of ultra-pure oleic acid

Crystallization and transformation mechanisms of ultrapure (99.999%) oleic acid were examined by Differential Scanning Calorimetry (DSC) and X-ray diffraction. X-ray diffraction spectra revealed three different polymorphs newly named α, β and γ, which differ from each other most significantly in the short spacing spectra. α and β were found to be equivalent to the previous data which Lutton named low and high melting polymorphs, whereas γ was newly identified in the present study. DSC studies have clarified the thermodynamic stability of the three polymorphs in a range of temperature from -20 to 16.2 C. β is always most stable, whereas α and γ are metastable, undergoing a reversible first-order solid-state transformation at -2.2 C (on heating). DSC also showed that the crystallization behaviors are strongly dependent on the polymorphs; α crystallizes at a much higher rate than β; despite the fact that they have close melting points (α, 13.3 C; β, 16.2 C). It was demonstrated for the first time that the above peculiar polymorphic behaviors of oleic acid are quite different from those of stearic acid, a saturated fatty acid with the same carbon chain length. Presented at the AOCS meeting in Philadelphia, May 1985.