Glyceride structure of fats

Summary A theory has been presented for the formation of fats which gives the amounts of the various glyceride types equivalent to a random or modified restricted random distribution and at the same time gives a predominance of specific positional isomers. The basis of the theory is a random attachment of the fatty acids at each stage of glyceride synthesis with an intramolecular rearrangement to a preferred form at the 1,2-diglyceride level of fat formation. The theory gives a good correlation of much of the data available on glyceride structure at the present time. Like all previous theories, the present proposal is based on the analysis of the final products of fat synthesis without any definite knowledge of the mechanism of the synthesis. Much more work is required on the glyceride structure of fats and the mechanism of their biosynthesis before the distribution pattern of the fatty acids in natural fats can be definitely established. Presented at fall meeting, American Oil Chemists' Socity, Chicago, Ill., October 20–22, 1958. Issued as N.R.C. No. 5416.     

Efficiency of transfer of polyunsaturated fats into milk

Polyunsaturated milk has been produced by feeding cows safflower oil enclosed in a casein coat protected with formaldehyde (SOC-F) or formaldehyde-treated soybean (SB) preparations. The efficiency of transfer of dietary 18∶2 ranged from 17 to 42% for various lots of SOC-F and was only 2–8% for SB (per cent transfer=18.2 in milk fat per dietary 18∶2×100). The 18∶2 content of the milk fat increased from basal levels of 2–3% of total fatty acids to 35% with certain SOC-F levels and 7% with SB. Major compensatory changes were noted in 14∶0 and 16∶0 fatty acids. Blood cholesterol, triglycerides and nonesterified fatty acids all increased markedly as cows were fed increasing amounts of SOC-F. There was no increase in cholesterol in the milk. Presented at the AOCS Meeting, Los Angeles, April 1972.     

Triglyceride composition of ewe,cow, and goat milk fat

The separation and identification of the components in milk fat, which are mainly triglycerides, is a challenge due to its complex composition. A reverse-phase high-performance liquid chromatography (HPLC) method with gradient elution and light-scattering detection is described in this paper for the triglyceride analysis in ewes’ milk fat. Triglyceride identification was carried out by combining HPLC, gas-liquid chromatography (GLC), and the calculated equivalent carbon numbers of several triglyceride standards. Quantitation of partially resolved peaks in the HPLC chromatogram was accomplished by applying a peak deconvolution program. Forty-four fatty acids were identified by GLC analysis, but only 19 were used for the following prediction of triglyceride molecular species; 181 triglycerides were identified, some of which were grouped at the same peak and needed application of the deconvolution program. Consequently, coefficients of variation were close to or lower than 5%. Moreover, the triglyceride composition of ewe, cow, and goat milk fat were compared by using these methods. These results show that ewe milk fat is richer in short- and medium-chain triglycerides, and cow milk fat is richer in long-chain and unsaturated triglycerides.     

Determination of the glyceride structure of fats. glyceride structure of fats with unusual fatty acid compositions

Five fats containing less common fatty acids, nutmeg butter (myristic), rapeseed oil (erucic, eicosenoic), peanut oil (arachidic, behenic, lignoceric), tung oil (eleostearic), and coriander seed oil (petroselinic) were oxidized, and the oxidized esterified glycerides were analyzed by gas-liquid chromatography (GLC). The values obtained are compared with those calculated from lipase hydrolysis data. Although there was a general over-all agreement between the compositions calculated from lipase hydrolysis data and that obtained by GLC analysis of the oxidized glycerides, there were some discrepancies that exceeded the range of experimental error. 1 Issued as N.R.C. No. 9626.     

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.     

Triglyceride analysis by gas chromatography in assessment of authenticity of goat milk fat

The triglyceride (TG) composition of 35 samples of milk collected at different times of year from five herds of goats was analyzed using short capillary column-gas chromatography. The distribution of TG in goat milk fat was unimodal, peaking at C₄₀ (12.6%); the sum of TG from C₃₈ to C₄₄ accounted for about 50%, whereas the three classes of TG from C₄₈ to C₅₂ did not exceed 6% each. These results were compared with the corresponding data for cow milk fat. Significant differences between herds were observed, mainly in long-chain TG. To detect foreign fats in goat milk fat, two multiple regression equations based on TG content of the goat milk fat were proposed. Analysis of known mixtures of tallow, palm oil, and cow milk fat with goat milk fat have experimentally confirmed the accuracy of the equations.     

TAG composition of ewe's milk fat. Detection of foreign fats

The TAG composition of 45 samples of ewe's milk, collected throughout the year from five Spanish breeds, was analyzed according to their carbon number by using short capillary column GC. The TAG content had a bimodal distribution with maxima at C₃₈ (12.8%) and C₅₂ (8.4%). The TAG composition did not vary significantly with respect to the time of year of sampling but was affected by the breed. Multiple regression equations based on TAG content are proposed to detect foreign fats in ewe's milk fat. Analysis of known mixtures of lard, palm oil, and cow's milk fat with ewe's milk fat have experimentally confirmed the accuracy of the equations.     

Iodine number determination of milk fat and vegetable fats by refractometry

A refractometric method for the estimation of iodine number of milk fat has been suggested. About 0.2 ml of milk fat was iodinated with ca. 10 ml Wijs iodine reagent for 3 min using mercuric acetate as catalyst. The iodinated fat showed a higher refractive index than the original fat. The changes in refractive indices showed a very high correlation with the iodine values of the fats (T=0.9993). The average of the ratios of change in refractive index to iodine number was 50.7×10⁻⁵, from which the iodine number of milk fat can be calculated. The method can also be applied to vegetable fats. The ratios of change in refractive index to iodine number for the oils of peanut, rapeseed, soybean, niger, sesame, and sunflower were similar, and the average was 45.2×10⁻⁵. The ratio for linseed oil was 38.4×10⁻⁵, and for coconut fat it was similar to that of milk fat.     

Determination of the glyceride structure of fats; analysis of 14 animal and vegetable fats

The glyceride compositions of seven animals and seven vegetable fats have been determined by GLC analysis of the oxidized esterified glycerides as described in an earlier paper in this series. The compositions determined are compared with those calculated from lipase hydrolysis data according to the method of VanderWal. Good agreement was found between the calculated and determined compositions for the majority of the 14 fats. The exceptions were human fat and the more satu-rated vegetable fats, palm oil and cocoa butter, where some discrepancies occurred. Issued as NRC No. 8052. National Research Council of Canada Postdoctorate Fellow.     

Influence of triacylglycerol structure and fatty acid profile of dietary fats on milk triacylglycerols in the rat. A two-generation study

We investigated the influence of dietary fatty acid profile and triacylglycerol structure on the fatty acid profile and triacylglycerol structure of milk lipids in two generations of rats. Three groups of rats received diets containing 20% fat of which approximately 20% was n-3 fatty acids located in different positions of the triacylglycerol: a fish oil-based diet [docosahexaenoic acid (22:6n-3) predominantly in thesn-2 position], a seal oil-based diet (22:6n-3) predominantly in thesn-1/sn-3 position or a plant oil-based diet [α-linolenic acid (18:3n-3) distributed evenly between the three positions]. This design allowed us to investigate (i) the effect of the triacylglycerol structure of the dietary fat; (ii) the effect of receiving the n-3 fatty acids as long-chain derivatives or as the precursor, 18:3n-3; and (iii) the long-term effects over two generations. The fatty acid profiles of the milk lipids largely reflected the diets, but in the second generation, the level of medium-chain fatty acids was higher (P<0.05) in the milk from rats fed the fish oil diet (24%) compared with the other dietary groups (15 and 18%). This suggests an increased endogenous synthesis of fatty acids in the mammary glands of the fish oil-fed rats. The levels of long-chain n-3 fatty acids in milk were higher (P<0.05) in rats fed maire n-3 fatty acids in milk were higher (P<0.05) in rats fed marie oils (8–12%) compared with rats fed vegetable oil (1%) in both generations. The level of long-chain n-3 fatty acids was significantly higher in the milk from the fish oil-fed rats (12.3%) compared to the seal-oil fed rats (8.0%) in the first generation, but not in the second generation (8.9 vs. 9.1%). The general structure of milk triacylglycerols was maintained in the three experimental groups with 16:0 acylated in thesn-2 position and 18:1 in thesn-1/sn-3 positions. The triacylglycerol structure of mammalian milk appears to be conserved even during extreme dietary manipulation over two generations and an extensive enrichment with long-chain n-3 polyunsaturated fatty acids requires their presence in the diet.     

Certain physical and chemical requirements of fats in the evaporated milk industry

Journal of the American Oil Chemists' Society -     

The structure and chemical composition of fats and oils

This is essentially a general review of progress during the past ten years both in the chemistry of the glycerides of fats and oils and in the chemistry and nature of their constituent fatty acids. Applications of some of the newer research methods are described and discussed. This paper was presented at the Symposium on the Chemistry & Metabolism of Fats, held at the Rochester meeting of the American Chemical Society. It is published here by special arrangement with the Division of Agricultural & Food Chemistry.     

A new approach to the glyceride structure of natural fats

Conclusions A new approach to the glyceride structure of natural fats has been achieved through the application of enforced interesterification to samples of animal and vegetable fats. The results obtained further substantiatte the hypothesis that animal fats, in contradistinction to seed fats, are essentially randomly distributed. Presented in part before the American Oil Chemists' Society conventicu in New Orleans, May 7–9, 1946.     

Fasting and postprandial lipid response to the consumption of modified milk fats by guinea pigs

The objective of the present study was to investigate the effect of three modified milk fats with different melting profiles on fasting and postprandial lipid responses and on fecal fat content in guinea pigs. We hypothesized that the consumption of modified milk fat with a high m.p. results in reduced fasting and postprandial lipid responses compared with that of modified milk fat fractions with lower m.p. To test this hypothesis, male Hartley guinea pigs were fed isoenergetic diets containing 110 g of fat/kg, either from one of the three modified milk fats with high (HMF), medium (MMF), or low melting profiles (LMF), or from one of the two reference fats as whole mil fat (MF) or a fat blend similar to that of nonhydrogenated soft margarine (MA) for 28 d. Food intake (P<0.05) and body weight gain (P<0.05) were reduced in the animals fed the HMF diet compared with the other groups. In the fasting state, plasma LDL cholesterol was highest in animals fed the LMF diet, intermediary in those fed the MMF and MF diets, and lowest in those fed the HMF and MA diets (P<0.05). Postprandially, the areas under the 0- to 3-h curves for the changes in plasma TG were lower in the HMF group than in the MA- and LMF-fed guinea pigs (P<0.05). The fecal fat content was higher (P<0.05) in the HMF group compared to the other milk fat groups. The present results suggest that modified milk fats can impact food intake, body weight gain, fasting cholesterolemia, and postprandial triglyceridemia, and these changes may be attributed to an altered fat absorption.     

Detection of interesterified fats in hydrogenated fats

Interesterification of fats is being used increasingly as an alternative to hydrogenation in preparing shortening and margarine bases. The detection of interesterified fats in vanaspati (a hydrogenated fat) is relevant because of possible adulteration problems. Either palmitic acid-rich or stearic acid-rich interesterified fats were blended with 13 market samples of hydrogenated fat (vanaspati) and examined by on-plate lipase hydrolysis of glycerides, gas chromatographic determination of fatty acids of the isolated 2-monoglycerides and calculation of two emperical indices. These were R₁, the ratio of the amounts of palmitic acid present in the 2-position to that in the total glyceride, and R₂, the ratio of saturated acid present in the 2-position to total saturated fatty acid in the fat. The vanaspati, R₁ was always below 10 and R₂ was always below 20. The presence of 5–10% interesterified fat raised both figures and offered a suitable basis for the detection of interesterified fats in hydrogenated fats.     

Estimating Thermodynamic Properties of Pure Triglyceride Systems Using the Triglyceride Property Calculator

To date, the most comprehensive model for predicting thermodynamic properties of pure triglycerides was presented by Wesdorp in “Liquid-multiple solid phase equilibria in fats: theory and experiments” (1990). In this paper, we present (1) corrections to the published model, as well as (2) a software implementation of the model for numerical assessment. The software tool, Triglyceride Property Calculator (TPC), uses a semi-empirical model to estimate the enthalpy of fusion and melting temperature for a given triglyceride based on its molecular composition and polymorphic form. These estimates are compared to experimentally collected data when available. The web application is available at http://www.crcfoodandhealth.com (under research tools) and through the AOCS Lipid Library. The quality of estimates is characterized according to defined counting metrics and presented for TAG subcategories. Additionally, the extrapolative value of the TPC is assessed by checking for consistency with underlying thermodynamic constraints. The current TPC implementation is effective in describing experimentally collected melting point data, with greater than 91% of the fitted values falling within 10% of the actual data. The TPC is also very good at describing collected enthalpy data. The underlying semi-empirical model and parameter set perform well in ensuring enthalpy predictions are thermodynamically consistent, however, extrapolated melting temperatures appear unreliable. Developing models and parameter sets that ensure thermodynamic consistency is a priority with future TPC iterations.     

Gelchromatographische Bestimmung polymerisierter Triglyceride

Determination of Polymerized Triglycerides by Gel Chromatography For separation of monomer polymerized triglycerides in deep frying fats a simple glas apparatus is described. Polystyrene ”?Biobeads S-X 2″ is used as separation material and dichlormethane as eluent. In used deep frying fats a correlation exists between the non polar fat components, determined by column chromatography, and polymerized triglycerides.     

Triglyceride composition of coconut oil

Triglycerides of coconut oil were fractionated by GLC into 13 groups based on their carbon numbers of 28 to 52. These groups represent 99.8% of the total glycerides of coconut oil. With the fatty acid composition of each group, it was possible to calculate the composition of 79 types of triglycerides. These types are defined by the nature of their constitutive fatty acids but the position of the acids on glycerol is unknown. Each group usually has only one major type of triglyceride. For example, group 36 has 52% of trilaurin. Also four types of triglycerides comprise 42.4% of the total glycerides and 24 types comprise 85%. The experimentally found distributions in each group are compared to the random distributions calculated from the fatty acid composition. For groups with carbon numbers 38 and 40, the experimental and random distributions were very similar but for most other groups, the distributions found were much different from the calculated random distributions.