C18:1, C18:2 and C18:3 trans and cis fatty acid isomers including conjugated cis delta 9, trans delta 11 linoleic acid (CLA) as well as total fat composition of German human milk lipids

Evaluation of two GC columns (60-m SUPELCOWAX 10 and 100-m CP Sil 88) for analysis of milkfat with emphasis on CLA, 18:1, 18:2 and 18:3 isomers, and short- and long-chain FA

Milkfat is a complex mixture of many diverse FA, some of which have demonstrated health benefits including anticancer properties. Attempts are under way to enrich milkfats with long-chain n-3 PUFA and CLA. It has been recommended that the analysis of these milkfats requires gas chromatography (GC) equipped with long, highly polar capillary columns. However, many analyses have been reported using CARBOWAX type (polyethylene glycol) capillary columns, such as SUPELCOWAX 10, even though the separation characteristics of many of the FA and their isomers present in milkfats have not been described in detail. This includes the isomers of CLA, cis- and trans-octadecenoic acid (18:1), linoleic acid (18:2n-6), and linolenic acid (18:3n-3), and the long-chain PUFA. On the other hand, the resolution of these FA and their isomers has been more fully described using the highly polar capillary columns, such as CP Sil 88 and SP2560 because of the improved resolution obtained using these polar columns. The present study was undertaken to characterize the separation of these FA present in milkfats using a 60-m SUPELCOWAX 10 column, to compare the results to those from a 100-m CP Sil 88 column, and to determine if these two columns could possibly serve to complement each other for the analysis of total milkfat. The advantages of the SUPELCOWAX 10 column were a better resolution of the short-chain saturated from their monounsaturated FA (MUFA) analogs, and a complete separation of the alpha-linolenic (18:3n-3) and eicosadecenoic acid (20:1) isomers. It also provided an alternative elution order of the linoleic (18:2n-6), 18:3n-3 and gamma-linolenic (18:3n-6) acid isomers. On the other hand, the CP Sil 88 column provided a better resolution of the CLA isomers, MUFA, the isolated cis and trans MUFA fractions, the PUFA, and many the 18:2n-6 and 18:3n-3 isomers. A complete analysis of milk lipids using the CP Sil 88 column required the prior separation of total FAME using silver ion-TLC. The results of the present study confirm that the 100-m highly polar capillary GC columns are mandatory for the analysis of milk lipids, and at best, the 60 m SUPELCOWAX 10 capillary column serves as a complementary GC column to provide different separations in certain regions based on its intermediate polarity.

Fatty acid composition and conjugated linoleic acid content of different tissues in rats fed individual conjugated linoleic acid isomers given as triacylglycerols small star, filled

HEAT TREATMENT OF VEGETABLE OILS GAVE RISE TO FOUR MAIN CONJUGATED LINOLEIC ACID (CLA) ISOMERS : the 9c,11t, 9t,11t, 10t,12c and 10t,12t. The diet of male Wistar rats was supplemented with 150 mg/day either 9c,11t-, 9t,11t-, 10t,12c- or 10t,12t CLA isomers for 6 days and their effects on lipid composition were investigated in liver, heart, skeletal muscle Gastrocnemius, kidneys, brain and adipose tissue. The incorporation of all isomers was low (< 1.4%) and the level was as follows : adipose tissue > Gastrocnemius > liver, kidneys > brain. The main changes in the overall lipid composition were observed in skeletal muscle (Gastrocnemius) and in heart and were associated with feeding the 10t,12c and 10t,12t isomers. The diet enriched in 10t,12t CLA decreased the total long chain polyunsaturated fatty acid proportion in Gastrocnemius (from 18.4% to 14.4%) and increased that of 20:4 n-6 in heart (from 16.9 to 19.3%). The diet enriched in 10t,12c CLA decreased the monounsaturated fatty acid proportion in Gastrocnemius (from 32.0 to 26.1%) and produced an effect similar to the 10t,12t in heart. By contrast, the 9c,11t and 9t,11t isomers did not affect fatty acid composition in all tissues and organs. We concluded that ingestion of 10t,12c and 10t,12t CLA present in oils and in CLA mixtures could change muscle lipid composition.

Comparative studies on individual isomeric 18:1 acids in cow, goat, and ewe milk fats by low-temperature high-resolution capillary gas-liquid chromatography

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 delta6-delta8 group, all trans-18:1 isomers with their ethylenic bonds between positions delta4 and delta16 (including the resolved critical pair delta13/delta14) were separated and quantitated individually. As expected, vaccenic (trans delta9-18:1) 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-delta12 isomer ranked third. The analytical procedure employed here appears a convenient alternative to oxidative-based procedures (generally ozonolysis), taking less time and alleviating some drawbacks of the latter procedure.

Study of individual trans- and cis-16:1 isomers in cow, goat, and ewe cheese fats by gas-liquid chromatography with emphasis on the trans-delta3 isomer

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 delta9 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-delta3 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 delta4 and delta14 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-delta9 (palmitelaidic) acid; consequently, these results were large over-estimates. Regarding the cis-16:1 acids, the delta9 isomer is the prominent constituent as expected, but the second-most important isomer is the delta13 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 trans18:1 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.

Follow-up of the delta4 to delta16 trans-18:1 isomer profile and content in French processed foods containing partially hydrogenated vegetable oils during the period 1995-1999. Analytical and nutritional implications

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 delta4 and delta16 for the two periods. The predominant isomer was delta9-18:1 (elaidic) acid, in the wide range 15.2-46.1% (mean, 27.9+/-7.2%) of total trans-18:1 acids, with the delta10 isomer ranked second, with a mean of 21.3% (range, 11.6 to 27.4%). The content of the unresolved delta6 to delta8 isomer group was higher than the delta11 isomer (vaccenic acid), representing on average 17.5 and 13.3%, respectively. Other isomers delta4, delta5, delta12, delta13/delta14, delta15, and delta16, 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 delta6-delta8 to delta10 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.