Content and distribution of trans ‐18:1 acids in ruminant milk and meat fats. Their importance in european diets and their effect on human milk

The trans ‐18:1 acid content and distribution in fats from ewe and goat milk, beef meat and tallow were determined by a combination of capillary gas‐liquid chromatography and argentation thin‐layer chromatography of fatty acid isopropyl esters. The trans isomers account for 4.5 ± 1.1% of total fatty acids in ewe milk fat (seven samples) and 2.7±0.9% in goat milk fat (eight samples). In both species, as in cow, the main isomer is vaccenic ( trans ‐11 18:1) acid. The distribution profile of trans ‐18:1 acids is similar among the three species. The contribution of ewe and goat milk fat to the daily intake of trans ‐18:1 acids was estimated for people from southern countries of the European Economic Community (EEC): France, Italy, Greece, Spain, and Portugal. It is practically negligible for most of these countries, but in Greece, ewe and goat milk fat contribute ca. 45% of the daily consumption of trans ‐18:1 acids from all dairy products (0.63 g/person/day for a total of 1.34 g/person/day). The trans ‐18:1 acid contents of beef meat fat (ten retail cuts, lean part) and tallow (two samples) are 2.0 ± 0.9% and 4.6%, respectively, of total fatty acids (animals slaughtered in winter). Here too, the main isomer is vaccenic acid. Other trans isomers have a distribution pattern similar to that of milk fat. Beef meat fat contributes less than one‐tenth of milk fat to the trans ‐18:1 acid consumed. The daily per capita intake of trans ‐18:1 acids from ruminant fats is 1.3–1.8 g for people from most countries of the EEC, Spain and Portugal being exceptions ( ca. 0.8 g/person/day). In France, the respective contributions of ruminant fats and margarines to the daily consumption of trans ‐18:1 acids are 1.7 and 1.1 g/person/day (60 and 40% of total, respectively). These proportions, based on consumption data, were confirmed by the analysis of fat from milk of French women (ten subjects). The mean content of trans ‐18:1 acids in human milk is 2.0 ± 0.6%, with vaccenic acid being the major isomer. Based on the relative levels of the trans ‐16 18:1 isomer, we could confirm that milk fat is responsible for the major part of the daily intake of trans ‐18:1 acids by French people. The daily individual intake of trans ‐18:1 isomers from both ruminant fats and margarines for the twelve EEC countries varies from 1.5 g in Spain to 5.8 g in Denmark, showing a well‐marked gradient from the southwest to the northeast of the EEC.