Trans- and cis-octadecenoic acid isomers in the hump and milk lipids from Camelus dromedarius

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 Camelu s dromedarius (the single-humped Arabian species) are described. Gas-liquid chromatography on two capillary columns with different polarities and leng ths were used for this purpose in combination with argentation thin-layer c hromatography. A comparison of the profiles established is made with that o f 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 positi ons between Delta4 and Delta 16. 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 ac id, followed by cis-vaccenic acid, as in true ruminant fats. Other cis isom ers encompass the Delta6-8 and the Delta 12 to Delta 15 isomers. Camelidae (suborder Tylopoda) and Bovidae (suborder Ruminantia) have evolved independ ently since the Eocene, that is for approximately 50 million years. Despite this considerable period, and the profound differences in anatomy, morphol ogy, physiology, ecological and dietary habits between the extant species o f these suborders, the rumen microflora has continued to synthesize the sam e trans- and cis-octadecenoic acid isomers, in comparable proportions, at l east as deduced from their composition profiles. We conclude that the trans -18:1 acid profile is not intrinsically species-dependent, but it can be af fected by the nature and the proportions of dietary unsaturated fatty acids that themselves depend on the feed, and that may be species-specific.