Composition and structure of some consumer-available edible fats

Stereospecific distribution of fatty acids in bovine milk fat triglycerides

Pancreatic lipase deacylation was used to study the variation in distribution of the fatty acids at positionsn-2 of milk fat triglycerides of a series of butters and of the milk obtained from a cow on a restricted feeding regimen. Selected samples were analysed for stereospecific distribution of their triglyceride fatty acids which were found to be esterified in a non-random manner. The percentage of a fatty acid at positionsn-3 generally decreased with increase in the chain length of the acid; the reverse occurred at positionsn-1. There was no major variation in the stereospecific distribution of fatty acids throughout the year; the variation that did occur was exhibited mainly by the medium chain length acids. Variation was greater at positionssn-1 andsn-3 than at positionsn-2 and when the proportion of an acid varied at positionsn-1 it usually varied at positionsn-3 in the reverse manner.

For the milk samples it was found that change in triglyceride fatty acid composition was not associated with random increases or decreases of fatty acids at the 3 stereospecific positions. With changing triglyceride fatty acid composition (6:0, 8:0, 10:0, 12:0, 14:0, and 16:0 decreasing and 18:1 increasing) the percentage of 6:0, 8:0, 10:0, 12:0, 14:0 and 16:0 acids at positionsn-3 decreased while the percentage of 18:0 and 18:1 acids increased. These changes were compensated for by changes in the opposite direction at positionssn-1 andsn-2.

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.

Impact of processing on formation of trans fatty acids

Trans fatty acids are formed during hydrogenation which is done to improve the functionality and oxidative stability of oils. Several process conditions affect the content of trans fatty acids in hydrogenated oil. There is conflicting evidence as to whether intake of trans fatty acids, in foods such as margarine, affects the types and levels of cholesterol produced in the blood. Epidemiological studies have shown associated increases in total cholesterol and low density lipoproteins, as well as decreased levels of high density lipo-proteins in the blood. It is unknown whether these effects are related directly to trans fatty acids or to the decrease of unsaturated fatty acids in the diet. This chapter will cover the recent nutritional status of trans fatty acids and the effect of processing on the levels of trans fatty acids in foods.

Trans fatty acids: implications for health, analytical methods, incidence in edible fats and intake (a review)

Trans fatty acids (TFA) are supposed to be related to a variety of physiological effects. Numerous studies in this field are gathered and compared, which mainly deal with the influences on lipoprotein levels in plasma and their effects with regard to coronary heart diseases. Furthermore, the analytical accessibility of trans fatty acids by different methods is presented. Thus, the most reliable method for an exact quantitation of trans fatty acids in edible fats is the combination of Ag-TLC with GC. The contents of TFA, in particular trans-octadecenoic acids, in bovine and human milk fat, in partially hydrogenated vegetable fats and oils as well as in processed food from different countries, determined in numerous studies, are summarized. Especially results on the isomeric distribution of positional isomers of trans-octadecenoic acid may be of future interest, since negative metabolic activities might only originate from certain isomers. Finally, intake rates of TFA in several countries are presented. It can be concluded that there still is need for further nutritional studies and that the discussion about TFA should not neglect the comparison with the saturated fatty acids C12, C14 and C16.

Competitive deposition of trans-12 and cis-9-octadecenoates into egg yolk lipids

The deposition of trans-12-octadencenoate-12(13)-3H (12t-18:1-3H) was compared to cis-9-octadecenoate-10-14C (9c-18:1-14C) in the major egg yolk neutral lipids and phospholipids trans-12-Octadecenoate was preferentially incorporated into cholesteryl esters (CE), phosphatidylcholines (PC), and phosphatidylethanolamines (PE) but was discriminated against in triglycerides (TG). Isotopic ratios indicate that 5.9 and 5.6 times more 12t-18:1-3H than 9c-18:1-14C was esterified at the 1-acyl position of PE and PC, respectively. The combined 1- and 3-acyl positions of TG and the 2-acyl position of TG, PE and PC were each preferentially esterified with 9c-18:1-14C.