The fate of carbon from long-chain fatty acids and glucose in dairy cows which were fed with protected fat was studied using stable isotope technique. The experiment was carried out on two groups of dairy cows (n=16 in each group) during the first 15 weeks of the lactation period. The cows were fed isoenergetic and isoproteinogenous diets based on corn silage. About 1.8 kg of tapioca starch in the diet of the starch group was substituted by about 0.7 kg of rumen protected fat (Ca salts of palm oil and soybean oil) in the diet of the fat group. The carbon atoms of dietary fat were naturally depleted in 13C as compared to carbon atoms of starch. Daily milk performance and lactose output were significantly (P < 0.05) higher among the cows fed with fat diet. In comparison to the starch group, the enrichment of milk fat with 13C was significantly lower, while that of breath CO2 was significantly higher in the fat group (P < 0.05). This means the fatty acids were incorporated into milk fat in preference to metabolic oxidation. Further studies showed that blood glucose is oxidized to a lower extent and is used for the synthesis of lactose to a higher proportion if the cows were fed with the fat diet. The glucose entry rate into the body glucose pool was not different between the diets. In conclusion, the dietary fatty acids perform a glucose sparing effect and improve the glucose supply for the mammary gland.

Besides the transpositional isomers of oleic acid (trans-C18:1) also cis/trans positional isomers of linoleic acid (transC18:2) are supposed to be related to a number of negative physiological effects. The trans-C18:2 area, comprising all isomers with at least one trans double bond, is rather complex and has been investigated little by gas chromatographic (GC) analysis so far. Depending on the analytical conditions, numerous overlaps between Cl 8:2 isomers, saturated or monounsaturated fatty acids (FA) occur. Based on several isothermal analyses on a highly polar 100-m GC column (1130, 140 to 190 degreesC) in combination with pre-separations using argentation thin-layer chromatography a separation of the trans Delta9,trans Delta12 isomer (t9t12), further trans-C-18:2 isomers as well as C18:1 isomers like cis Delta16-C18:1 could be achieved. The isomer t9t12 is of particular interest from the viewpoint of nutritional physiology. Furthermore, mass spectrometric analysis allowed the identification of the rarely described 11-cyclohexylundecanoic FA. Depending on the column temperature, this FA shifts across a wide range of the C1 8:1/C18:2 isomeric region leading to many quantitative falsifications as a result of overlaps with other peaks. In 100 milk fats mean contents of t9t12 and the cyclohexyl FA of 49 +/- 24 mg/100 g and 0.16 +/- 0.03 g/100 g FA could be established. Additionally, interferences of the linoleic acid peak with trans Delta11,cis Delta15-C18:2, cis Delta9,cisDelta15-C18:2 and C19:1 could be demonstrated, resulting in an overestimation of linoleic acid of up to 86% at certain column temperatures.

The aim of our study was to explore whether the substitution of starch by rumen protected fatty acids in diets of dairy cows results in a transfer of carbon atoms from lipids into milk lactose. Because the carbon atoms of fat are naturally depleted in C-13 as compared to carbon atoms of carbohydrates we hypothesized that the 13C content in milk lactose is lower when dietary fat carbon atoms are used for lactose synthesis. For this purpose the C-13/C-12 ratio in milk lactose, fat, and in blood CO2 of samples from Holstein-Friesian cows was assessed weekly during the first 15 weeks of lactation. Treatments consisted of a corn silage-based diet supplemented with starch (control, C) or protected fatty acids (calcium salts, CS). Treatments were isoenergetic and isonitrogenous. The following results were found (C/CS, Mean+/-SEM): milk yield 38.8+/-1.7/41.5+/-1.0 kg/d; milk protein 3.1+/-0.05/2.9+/-0.03% (P<0.05); milk fat 4.3+/-0.2/4.0+/-0.2%; milk lactose 4.7+/-0.03/4.7+/-0.03%; milk urea 217+/-6/242+/-8 mg/l (P<0.05); blood glucose 3.5+/-0.08/3.4+/-0.05 mmol/l. Carbon atoms in the milk fat of the CS group were C-13-depleted in comparison to the milk fat of the C group (P<0.05). The C-13 level in milk lactose did not differ between the groups. Surprisingly the C-13 in blood CO2 of the C group was depleted in comparison to the CS group. It can be concluded that the entry of C-13-depleted carbon atoms from fatty acids into the citric acid cycle seems to be inhibited by dietary fatty acids. Transfer of carbon atoms from fatty acids into lactose by the citric acid cycle and gluconeogenesis from oxalacetate is apparently not enhanced by feeding protected fat.

LipidsVolume 37, Issue 12 p. 1149-1150 Letter to the Editor Reassessment of the contribution of bovine milk fats to the trans-18:1 isomeric acid consumption by European populations. Additional data for rumenic (cis-9,trans-11 18:2) acid Robert L. Wolff, Robert L. Wolff INRA, UNL, Dijon cedex, 21065 France Deceased.Search for more papers by this authorDietz Precht, Corresponding Author Dietz Precht [email protected] Federal Dairy Research Centre, Institute of Dairy Chemistry and Technology, P.O. Box 6069, Kiel, 24121 GermanyTo whom correspondence should be addressed at Institute of Dairy Chemistry and Technology, Federal Dairy Research Center, P.O. Box 6069, 24121 Kiel, Germany. E-mail: [email protected]Search for more papers by this author Robert L. Wolff, Robert L. Wolff INRA, UNL, Dijon cedex, 21065 France Deceased.Search for more papers by this authorDietz Precht, Corresponding Author Dietz Precht [email protected] Federal Dairy Research Centre, Institute of Dairy Chemistry and Technology, P.O. Box 6069, Kiel, 24121 GermanyTo whom correspondence should be addressed at Institute of Dairy Chemistry and Technology, Federal Dairy Research Center, P.O. Box 6069, 24121 Kiel, Germany. E-mail: [email protected]Search for more papers by this author First published: 01 December 2002 https://doi.org/10.1007/s11745-002-1013-0Citations: 20 Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume37, Issue12December 2002Pages 1149-1150 RelatedInformation

The objective of this study was to determine the effect of a dairy cows diet supplemented with rumen protected fat on the proportions of cis and trans isomers of C16:1, C18:1 and C18:2 in milk fat. Further, the effect of this diet on the level of different conjugated linoleic acid (CLA) isomers should be investigated. Milk fat samples from high yielding Holstein-Friesian cows fed a control diet (n=1 6) or a diet supplemented with rumen protected fatty acids (Ca soaps, CS; n=1 6) were collected weekly during the first 15 weeks of lactation. With argentation thin-layer chromatography followed by low-speed high-resolution-gas chromatography on a 100-m capillary column 11 trans-Cl 6:1, 11 trans-Cl 8:1 isomers, as well as 8 cis-C18:1 isomers including the rarely described cis Delta16-C18:1 isomer were separated and quantified. Furthermore, 8 cis/trans-C18:2 isomers and 7 CLA isomers were determined. With special gas chromatographic conditions it was possible to identify t9t12-C18:2 without overlaps with other isomers. The results show that the content of denovo synthesized fatty acids (FA) in milk fat was reduced by the CS diet and that the dietary lipids were not completely protected from ruminal biohydrogenation. Increases of more than 150% were observed for t6-8, t13-14, cl 2, c9t12 as well as for the CLA isomers t10c12 and t9t11 in the CS group. The relative trans-Cl 8:1 isomeric profile of the milk fats in the CS group corresponded to the typical composition of winter milk fat during the barn feeding period, although the high oleic content as well as the high total content of trans-C18:1 FA pointed to the typical "soft" milk fat from the pasture feeding period in summer. The relative isomeric contributions of trans-Cl 8:1, cis-C18:1, trans-Cl 8:2 and CLA isomers demonstrate that the CS diet had no fundamental influence on biohydrogenation mechanism in the rumen concerning trans octadecenoic acids, besides the increase in the total amount of all these isomers. However, the especially high levels of c 12 or of certain trans-Cl 8:2 and CLA isomers point out that biohydrogenation does play a certain role concerning their origin under CS feeding conditions.

LipidsVolume 37, Issue 6 p. 627-629 Letter to the Editor A critique of 50-m CP-Sil 88 capillary columns used alone to assess trans-unsaturated FA in foods: The case of the TRANSFAIR study Robert L. Wolff, Robert L. Wolff INRA, UNL, B.P. 86510, 17, rue Sully, Dijon Cedex, 21065 FranceSearch for more papers by this authorDietz Precht, Corresponding Author Dietz Precht [email protected] Institute of Dairy Chemistry and Technology, Federal Dairy Research Center, Kiel, 24121 GermanyTo whom correspondence should be addressed at INRA, UNL, 17, rue Sully, B.P. 86510, 21065 Dijon Cedex, France. E-mail: [email protected]Search for more papers by this author Robert L. Wolff, Robert L. Wolff INRA, UNL, B.P. 86510, 17, rue Sully, Dijon Cedex, 21065 FranceSearch for more papers by this authorDietz Precht, Corresponding Author Dietz Precht [email protected] Institute of Dairy Chemistry and Technology, Federal Dairy Research Center, Kiel, 24121 GermanyTo whom correspondence should be addressed at INRA, UNL, 17, rue Sully, B.P. 86510, 21065 Dijon Cedex, France. E-mail: [email protected]Search for more papers by this author First published: 01 June 2002 https://doi.org/10.1007/s11745-002-0942-yCitations: 24AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article.Citing Literature Volume37, Issue6June 2002Pages 627-629 RelatedInformation

The objective of this study was to evaluate the effect of individual C18 isomers on milk fat depression (MFD) and on milk yield from high-yielding cows in early lactating period (week 2 to 15 postpartum (p.p.)) by feeding a high fiber ration. Milk fat samples from 16 Holstein-Friesian cows of a control group and from 16 cows with Ca soaps (CS) of fatty acids supplementation (75% palm fat, 25% sunflower and soybean oil) were weekly collected during the first 15 lactation weeks. In the CS group one-third of the starch (relative to the control group) was substituted with the protected fat on an energy equivalent basis. In the CS group a decrease in the milk fat content (FC) by 17.6% and an increase in the milk yield by 23.9% was observed during week, 13 to 14. Statistically significant relationships were calculated between FC and the isomers trans A 6-8 (t6-8; r= -0.76), t9 (r= -0.78) and cl 2 (r=-0.74) after week 13 to 14. With the used high fiber CS diet t6-8 and cl 2 in milk fat proved to be important isomers indicating MFD and simultaneously demonstrating the greatest increase from the control diet to the CS feeding. When considering all 15 lactation weeks in the CS group, the isomer cl 2 again showed the highest correlation (r= -0.98) and the conjugated linoleic acid (CLA) c9t11 the second highest r-value (r=-0.95) in relation to FC.

LipidsVolume 36, Issue 2 p. 213-217 Letter to the Editor Overestimates of oleic and linoleic acid contents in materials containing trans fatty acids and analyzed with short packed gas chromatographic columns Dietz Precht, Corresponding Author Dietz Precht [email protected] Institute of Dairy Chemistry and Technology Federal Dairy Research Centre, PO Box 60 69, Kiel, D-24121 Germany [email protected] [email protected] [email protected] [email protected]Search for more papers by this authorJoachim Molkentin, Joachim Molkentin Institute of Dairy Chemistry and Technology Federal Dairy Research Centre, PO Box 60 69, Kiel, D-24121 GermanySearch for more papers by this authorMark A. McGuire, Corresponding Author Mark A. McGuire [email protected] Department of Animal and Veterinary Science, University of Idaho, Moscow, Idaho, 83844 [email protected] [email protected] [email protected] [email protected]Search for more papers by this authorMichelle K. McGuire, Corresponding Author Michelle K. McGuire [email protected] Department of Food Science and Human Nutrition, Washington State University, Pullman, Washington, 99164 [email protected] [email protected] [email protected] [email protected]Search for more papers by this authorRobert G. Jensen, Corresponding Author Robert G. Jensen [email protected] 186 Chaffeeville Rd., Storrs, Connecticut, 06268-2637 [email protected] [email protected] [email protected] [email protected]Search for more papers by this author Dietz Precht, Corresponding Author Dietz Precht [email protected] Institute of Dairy Chemistry and Technology Federal Dairy Research Centre, PO Box 60 69, Kiel, D-24121 Germany [email protected] [email protected] [email protected] [email protected]Search for more papers by this authorJoachim Molkentin, Joachim Molkentin Institute of Dairy Chemistry and Technology Federal Dairy Research Centre, PO Box 60 69, Kiel, D-24121 GermanySearch for more papers by this authorMark A. McGuire, Corresponding Author Mark A. McGuire [email protected] Department of Animal and Veterinary Science, University of Idaho, Moscow, Idaho, 83844 [email protected] [email protected] [email protected] [email protected]Search for more papers by this authorMichelle K. McGuire, Corresponding Author Michelle K. McGuire [email protected].edu Department of Food Science and Human Nutrition, Washington State University, Pullman, Washington, 99164 [email protected] [email protected] [email protected] [email protected]Search for more papers by this authorRobert G. Jensen, Corresponding Author Robert G. Jensen [email protected] 186 Chaffeeville Rd., Storrs, Connecticut, 06268-2637 [email protected] [email protected] [email protected] [email protected]Search for more papers by this author First published: 01 February 2001 https://doi.org/10.1007/s11745-001-0710-zCitations: 19AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL REFERENCES 11. Wolff, R.L., Combe, N.A., Precht, D., Molkentin, J., and Ratnayake, W.M.N. (1998) Accurate Determination of trans-18:1 Isomers by Capillary Gas–Liquid Chromatography on Cyanoalkyl Polysiloxane Stationary Phases, Oleagineaux, Corps Gras Lipides 5, 295– 299. 22. Wolff, R.L., and Bayard, C.C. (1995) Improvement in the Resolution of Individual Trans-18:1 Isomers by Capillary Gas–Liquid Chromatography: Use of a 100-m CP-Sil 88 Column, J. Am. Oil Chem. Soc. 72, 1197– 1201. 33. Precht, D., and Molkentin, J. (1995) Trans Fatty Acids: Implications for Health, Analytical Methods, Incidence in Edible Fats and Intake, Nahrung 39, 343– 374. 44. Chen, Z.Y., Pelletier, G., Hollywood, R., and Ratnayake, W.M.N. (1995) Trans Fatty Acid Isomers in Canadian Human Milk, Lipids 30, 15– 21. 55. Sheppard, A.J., Iverson, J.L., and Wierauch, J.L. (1978) Composition of Selected Dietary Fats, Oils, Margarines, and Butter, in Handbook of Lipid Research: 1. Fatty Acids and Glycerides ( A. Kuksis, ed.), pp. 341– 379, Plenum Press, New York. 66. Palmquist, D.L., Beaulieu, A.D., and Barbano, D.M. (1993) Feed and Animal Factors Influencing Milk Fat Composition, J. Dairy Sci. 76, 1753– 1771. 77. Harzer, G., Haug, M., Dieterich, I., and Gentner, P.R. (1983) Changing Patterns of Human Milk Lipids in the Course of the Lactation and During the Day, Am. J. Clin. Nutr. 37, 612– 621. 88. Wolff, R.L., Precht, D., and Molkentin, J. (1998) Trans-18:1 Acid Content and Profile in Human Milk Lipids. Critical Survey of Data in Connection with Analytical Methods, J. Am. Oil Chem. Soc. 75, 661– 671. 99. Precht, D., and Molkentin, J. (1999) C18:1, C18:2 and C18:3 trans and cis Fatty Acid Isomers Including Conjugated cis δ 9,trans δ 11 Linoleic Acid (CLA) as Well as Total Fat Composition of German Human Milk Lipids, Nahrung 43, 233– 244. 1010. Precht, D., and Molkentin, J. (2000) Recent Trends in the Fatty Acid Composition of German Sunflower Margarine, Shortenings and Cooking Fats with Emphasis on Individual C16:1, C18:1, C18:2, C18:3 and C20:1 trans Isomers, Nahrung 44, 222– 228. 1111. Precht, D., and Molkentin, J. (1997) Trans-Geometrical and Positional Isomers of Linoleic Acid Including Conjugated Linoleic Acid (CLA) in German Milk and Vegetable Fats, Fett/Lipid 99, 319– 326. 1212. Precht, D., and Molkentin, J. (1996) Rapid Analysis of the Isomers of trans-Octadecenoic Acid in Milk Fat, Int. Dairy J. 6, 791– 809. 1313. Craig-Schmidt, M.C. (1998) Worldwide Consumption of trans Fatty Acids, in Trans Fatty Acids in Human Nutrition ( J.L. Sébédio, and W.W. Christie, eds.), pp. 59– 113, The Oily Press Ltd., Dundee. 1414. McGuire, M.A., McGuire, M.K., Griinari, J.M., Nurmela, K.V.V., Park, Y.S., and Shultz, T.D. (1998) Regulation of Human Milk Fat Synthesis by Trans Fatty Acids, FASEB J. 12, A202. 1515. Wolff, R.L., Precht, D., and Molkentin, J. (1998) Occurrence and Distribution Profiles of trans-18:1 Acids in Edible Fats of Natural Origin, in Trans Fatty Acids in Human Nutrition ( J.L. Sébédio, and W.W. Christie, eds.) pp. 1– 33, The Oily Press Ltd., Dundee. Citing Literature Volume36, Issue2February 2001Pages 213-217 ReferencesRelatedInformation

The aim of this study was to determine the effects of a diet supplemented with rumen-protected linoleic acids (C18:2) on the composition of milk fat and the energy balance of dairy cattle during the first 15 wk of lactation. The 32 Holstein-Friesian cows were allotted in two treatment groups; in the experimental group one-third of the starch (relative to the control group) was substituted with protected fat on an energy basis. Milk samples from all cows were collected weekly from week 2 to 15 postpartum (p.p.). To analyze the milk fat composition milk samples from 16 cows in each group were collected from week 6 and 7 as well as from week 13 and 14 p.p. and were mixed together, respectively. Triglyceride analysis demonstrated an extensive use of depot fat in both cow groups at the beginning of the lactation period. However, calculated energy balance, triglyceride composition and back fat thickness showed that the usual deficit of energy intake in early lactation was significantly shortened in the experimental group by three weeks. In comparison with the control group the content of the saturated fatty acids (FAs) C12, C14 and C16 in the experimental group decreased by 17.3% at 6 to 7 wk and by 19.2% at 13 to 14 wk. The stearic acid content of milk fat was increased by 25.9% at 6 to 7 wk and by 27.7% at 13 to 14 wk in the experimental group. The content of cis Delta9 oleic acid was increased by 21.6% at 6 to 7 and by 30.3% at 13 to 14 wk, while the C18:2 FA content was doubled as compared with the control group. Thus besides the increase of the trans-C-18:1 FA (TFA) content the nutritional value of fats could be improved using the experimental fat supplement. The TFA content still remained within the range of variation of natural milk fats. Additionally the experimental fat intake led to a number of desired effects; an increase in the content of conjugated linoleic acids (cis Delta9,trans Delta11) by 55.9% (6 to 7 wk) and by 97.1% (13 to 14 wk p.p.), respectively, and a decrease in the cholesterol level. Further, the butyric acid content increased relatively by more than 20%. The addition of this fat resulted simultaneously in a changed triglyceride composition with increased C50, C52 and C54 contents. Thus a markedly improved spreadability of the resulting butter might be expected.

Data about the cholesterol content in edible fats like bovine milk fat are important for balancing the cholesterol intake with food. A comparison of 3 different cholesterol determination methods showed that with the direct analysis by a 25 m long TAP steel capillary column the same results could be obtained as with a time-consuming saponification standard method including thin-layer chromatographic cleaning and subsequent silylation. On the other hand with a rapid direct method using a short packed column 21% unsaponifiables as e.g. minor sterols or hydrocarbons could be found in the "cholesterol peak". The analysis of 1142 German milk fats led to a mean cholesterol content of 265.6 +/- 20.0 mg/100 g fat (range: 204.4 to 382.5). For 165 milk fats from other 12 EU-countries, a similar mean cholesterol content of 258.5 +/- 19.9 mg/100 g fat (range: 215.0 to 331.6) was detected. Compared with sufficiently fed cows, underfed cows demonstrated an approx. 10.1% lower mean cholesterol content (238.7 +/- 9.7 mg/100 g fat). On the other hand, during the first 7 days post partum, the colostrum showed a significantly higher mean cholesterol content of 327.2 +/- 99.0 mg/100 g fat (n = 15; range: 213.1 to 583.9). Further, with special conditions as feeding of rape-seed the cholesterol content can be significantly lowered by 8-13%. An extraordinary lowering up to 50% can be reached by dry fractionation of milk fat (stearin "hard" fraction).

The distribution profiles of individual trans- as well as cis-18∶1 isomers from the fat prepared from the hump adipose tissue and the milk from Camelus dromedarius (the single-humped Arabian species) are described. Gas-liquid chromatography on two capillary columns with different polarities and lengths were used for this purpose in combination with argentation thin-layer chromatography. A comparison of the profiles established is made with that of true ruminant fats. In the fats from the dromedarius as well as from true ruminants, the trans-18∶1 isomers have their ethylenic bonds in all positions between Δ4 and Δ16. The prominent trans isomer is the 11–18∶1 (vaccenic) acid in all species, and the complete distribution profiles are quite similar. Concerning the cis isomers, the prominent isomer is oleic acid, followed by cis-vaccenic acid, as in true ruminant fats. Other cis isomers encompass the Δ6–8 and the Δ12 to Δ15 isomers. Camelidae (suborder Tylopoda) and Bovidae (suborder Ruminantia) have evolved independently since the Eocene, that is for approximately 50 million years. Despite this considerable period, and the profound differences in anatomy, morphology, physiology, ecological and dietary habits between the extant species of these suborders, the rumen microflora has continued to synthesize the same trans- and cis-octadecenoic acid isomers, in comparable proportions, at least as deduced from their composition profiles. We conclude that the trans-18∶1 acid profile is not intrinsically species-dependent, but it can be affected by the nature and the proportions of dietary unsaturated fatty acids that themselves depend on the feed, and that may be species-specific.

The trans- as well as the cis-18∶1 isomer profiles were established in cow, goat, and ewe cheese fats, with the assumption that these are representative of the corresponding milks. Argentation thin-layer chromatography was combined with low-temperature high-resolution gas-liquid chromatography on 100-m highly polar capillary columns, thus adding precision to earlier data for these species. Despite differences in the absolute content of trans-18∶1 isomers between species, the relative profiles were essentially similar. Except for the minor trans Δ6–Δ8 group, all trans-18∶1 isomers with their ethylenic bonds between positions Δ4 and Δ16 (including the resolved critical pair Δ13/Δ14) were separated and quantitated individually. As expected, vaccenic (trans Δ9−18∶1) acid was the main isomer, accounting for as much as 37 to 50% of the total fraction. It was observed that the goat trans-18∶1 isomer profile was usually rather close to that of cows in winter (barn feeding), whereas that of the ewe shows a seasonal dependence. The trans-18∶1 profile of ewe milk fats from this study resembles that of cows in the transition period between winter and summer (pasture) feeding. Regarding the cis-18∶1 acid fraction, two isomers (oleic and cis-vaccenic acids) accounted for ca. 97% of that fraction for the three species, with the cis-Δ12 isomer ranked third. The analytical procedure employed here appears a convenient alternative to oxidative-based procedures (generally ozonolysis), taking less time and alleviating some draw-backs of the latter procedure.

Low-temperature gas-liquid chromatography (GLC) was applied to study the distribution profiles of isomeric trans-and cis-hexadecenoic acids in ruminant (cow, goat, and ewe) milk fat after their fractionation by argentation thin-layer chromatography (Ag-TLC). The fat was extracted from cheeses (12 samples of each species), the most common foods made with goat and ewe milks. The predominant trans-16∶1 isomer is palmitelaidic acid (the Δ9 isomer), but it does not exceed one-third of the total group, which itself represents 0.17% (cow), 0.16% (goat), and 0.26% (ewe) of the total fatty acids. The trans-Δ3 16∶1 isomer, which is reported for the first time in ruminant lipids and which likely comes from the animals' feed, is present at a level of ca. 10% of the trans-16∶1 acid group. Otherwise, all isomers with their ethylenic bond between positions Δ4 and Δ14 are observed in the three species studied, roughly showing the same relative distribution pattern. Quantitatively, the trans-16∶1 isomers only represent ca. 5% of the sum of the trans-16∶1 plus trans-18∶1 isomers, and they appear of little importance in comparison. It is inferred from this and recent studies that some previously reported data that were established for consumption assessments dealt in fact mainly with iso-17∶0 acid, which was confused with (and added to) trans-Δ9 (palmitelaidic) acid; consequently, these results were large overestimates. Regarding the cis-16∶1 acids, the Δ9 isomer is the prominent constituent as expected, but the second-most important isomer is the Δ13 isomer. It does not appear that trans-16∶1 isomers are from ruminant milk fats of great nutritional importance as compared with trans-18∶1 isomeric acids. As for trans-18∶1 isomers, the combination Ag-TLC/GLC is a necessary procedure to quantitate trans-16∶1 acids accurately and reliably. Ag-TLC allows removal of interfering branched 17∶0 acids and cis-16∶1 acids, and low-temperature GLC permits an accurate measurement of all individual isomers most of which with baseline resolution.

The intake of trans C18:1 as well as of trans hexadecenoic acids (trans C16:1) is believed to be related with numerous physiological disadvantages, such as the risk of coronary heart disease. Since most of the existing data on trans C16:1 contents in human milk fat have been determined without a pre-separation by thin-layer chromatography (TLC), the gas chromatographically determined contents of trans C16:1 frequently are too high due to overlaps with C17 fatty acids. Using a highly polar column with a length of 100 m after AgNO3-TLC allowed to establish an average content of total trans C16:1 of 0.15 ±0.04% from 39 samples of human milk fat. Moreover, the C16:1 positional isomers trans Δ4, Δ5, Δ6/7, Δ8, Δ9, Δ10, Δ11, Δ12, Δ13 and Δ14 could be quantified from 15 samples exhibiting mean relative contents of 2.6, 3.5, 7.6, 7.2, 24.7, 10.4, 10.1, 14.3, 8.4 and 11.3% related to the total trans C16:1 content, respectively. Also, the C16:1 isomer trans Δ3 could be identified occurring in traces with a mean absolute content of 2 mg/100 g fatty acids. A baseline separation of almost all trans isomers could be achieved for the first time. Further, mass spectrometric analyses of FAME and DMOX derivatives allowed to identify the isomer trans Δ4. Among the C16:1 isomers cis Δ7 to cis Δ14 the isomer cis Δ9 predominated with a relative proportion of 68.3% and an absolute content of 1.88% of all fatty acids. Correspondingly, among the C17:1 isomers cis Δ7 to cis Δ11 the isomer cis Δ9 with 82.6% had the highest relative content.

A survey of the total content of trans-18∶1 acids and their detailed profile in French food lipids was conducted in 1995–1996, and 1999. For this purpose, 37 food items were chosen from their label indicating the presence of partially hydrogenated vegetable oils (PHVO) in their ingredients. The content as well as the detailed profile of these isomers was established by a combination of argentation thin-layer chromatography and gas-liquid chromatography (GLC) on long polar capillary columns. With regard to the mean trans-18∶1 acid contents of extracted PHVO, a significant decrease was observed between the two periods, i.e., from 26.9 to 11.8% of total fatty acids. However, only minor differences were noted in the mean relative distribution profiles of individual trans-18∶1 isomers with ethylenic bonds between positions Δ4 and Δ16 for the two periods. The predominant isomer was Δ9–18∶1 (elaidic) acid, in the wide range 15.2–46.1% (mean, 27.9±7.2%) of total trans-18∶1 acids, with the Δ10 isomer ranked second, with a mean of 21.3% (range, 11.6 to 27.4%). The content of the unresolved Δ6 to Δ8 isomer group was higher than the Δ11 isomer (vaccenic acid), representing on average 17.5 and 13.3%, respectively. Other isomers Δ4, Δ5, Δ12, Δ13/Δ14, Δ15, and Δ16, were less than 10% each: 1.0, 1.6, 7.4, 7.1, 1.8, and 1.0%, respectively. However, considering individual food items, it was noted that none of the extracted PHVO were identical to one another, indicating a considerable diversity of such fats available to the food industry. A comparison of data for French foods with similar data recently established for Germany indicates that no gross differences occur in PHVO used by food industries in both countries. Estimates for the absolute mean consumption of individual isomers from ruminant fats and PHVO are made for the French population and compared to similarly reconstructed hypothetical profiles for Germany and North America. Differences occur in the total intake of trans-18∶1 acids, but most important, in individual trans-18∶1 isomer intake, with a particular increase of the Δ6–Δ8 to Δ10 isomers with increasing consumption of PHVO. It is inferred from the present and earlier data that direct GLC of fatty acids is a faulty procedure that results (i) in variable underestimates of total trans-18∶1 acids, (ii) in a loss of information as regards the assessment of individual isomeric trans-18∶1 acids, and (iii) in the impossibility of comparing data obtained from human tissues if the relative contribution of dietary PHVO and ruminant fats is not known.

Gas-chromatographic analysis of butyric acid (C4) in mixed spreadable fats can be used to calculate the milk fat proportion, either by additional analysis of the underlying pure milk fat (component sample) or by using a mean C4 content instead. After comparison of several analytical variants and subsequent development of an improved draft standard for quantitation of milk fat in mixed fats, this draft was checked for accuracy in three EU-wide ring tests performed with 26 participating laboratories. Due to the natural variation of the butyric acid content in European milk fats, deviations from the actual milk fat content may amount up to +/-10% in addition to analytical errors when calculating with a mean C4 content instead of the C4 content of a component sample. Though the reproducibility could be improved by application of correction factors derived from a reference fat, only the calculation based on the additional analysis of a component sample of the pure milk fat led to an acceptable accuracy concerning the trueness of the results in combination with good repeatability (r) and reproducibility (R). Finally, several further improvements of the draft standard led to a precision of r = 4.3% and R = 6.0% relative to the mean of two milk fat contents determined. Thus, the tested procedure proved its suitability for a control method of the declared milk fat content in mixed fat spreads.

In some countries the content of trans fatty acids (TFA) in margarines has strongly decreased as a result of the continuous discussion on their disadvantages regarding aspects of nutritional physiology. However, still in 1994 almost 1/3 of total fatty acids in part of German sunflower margarines, shortenings and cooking fats comprised these unfavourable TFA. In the present study the main interest was laid on trans-C16:1, trans-C18:1, trans-C20:1, trans-C18:2 and trans-C18:3 fatty acids and particularly their individual isomers, as negative metabolic activity of TFA possibly might only be attributable to certain isomers. By combining argentation thin-layer chromatography with gas chromatography using a 100-m capillary column (CP-Sil 88) trans fatty acid contents were determined in nearly all German brands of sunflower margarines (SFM; n = 9) and of cooking fats and shortenings (CFS; n = 10). Concerning the above-mentioned groups of isomers mean TFA contents of 0.01, 4.88, 0.00, 0.45 and 0.03% for SFM as well as of 0.01, 5.02, 0.03, 0.70 and 0.17% for CFS were established, respectively. The re-evaluation of samples from 1994 and 1996 exhibited that the total TFA content (sum of all mentioned isomers) in SFM decreased from 21.77% (range: 13.78-26.29; n = 11) to 5.37% (1.98-6.15%; n = 9) between 1994 and 1999. Also the total TFA content in CFS on average strongly decreased from 11.77% (0.08-33.63; n = 16) in 1994 and 12.52% (1.61-26.79%; n = 7) in 1996 to 5.91% (0.43-19.72%; n = 10) in 1999. However, even the newest CFS samples partly exhibited relative high TFA contents. In addition to the total TFA contents all positional isomers of trans-C18:1, trans-C18:2 and trans-C18:3 in SFM and CFS were quantified and compared between different years. The conjugated linoleic acid (cis delta 9, trans delta 11) occurred only in small amounts of 0.03% and 0.02% in current SFM and CFS.

From a great number of European bovine milk fats (up to 2110 samples) frequency distributions of the contents of conjugated linoleic acid (c9t11-C18:2) as well as of the trans fatty acids (TFA) trans-C18:1, trans-C18:2, t11-C18:1 (vaccenic acid), t11c15-C18:2 (main isomer of trans-C18:2) and of total TFA were established considering different normal feeding conditions (barn feeding, pasture feeding and feeding in the transition periods in spring and late autumn). In addition to the average contents of c9t11 (0.76%), trans-C18:1 (3.67%), trans-C18:2 (1.12%) and total TFA (4.92%) the corresponding variation ranges of 0.13-1.89%, 1.29-7.17%, 0.30-2:04% and 1.71-8.70%, respectively, were determined in these EU milk fats using a combination of Ag-TLC and GC. High correlation coefficients (r) between the contents of the CLA isomer c9t11 and the contents of trans-C18:1, trans-C18:2, total TFA and C18:3 of 0.97, 0.91, 0.97 and 0.89, respectively, could be calculated. Another high correlation with r=.89 between C18:3 and t11c15-C18:2 points at a probable metabolic pathway in the biohydrogenation of linolenic acid (c9c12c15 --> c9t11c15 --> t11c15 --> t11).