Methyl-branched fatty acids and chiral anteiso-fatty acids in neutral and polar lipids of biological samples

Fatty acids (FA) are ubiquitously found in nature, where they represent the basic building blocks of naturally occurring lipids of living organisms. In most cases, FA are chemically bound to a glycerol backbone, either in the form of the acylglycerols, which belong to the group of neutral lipids (typically >80% of food lipids), or in the form of phospholipids, the polar lipids (typically <1-20% of food lipids). Only a small proportion of FA occurs in the free form or is linked to backbones other than glycerol. Fatty acids in these molecules are responsible for a variety of distinct biological and physiological properties. More than one thousand FA are present in nature but only a low percentage of them are widespread throughout biological samples. The main FA are saturated or cis-unsaturated and contain an even number of carbon atoms. A multitude of other FA, however, can be found in trace amounts. For instance, the trans-FA or the methyl-branched FA, namely the iso- and anteiso- FA, are characteristic representatives of the minor FA. The latter are distinctive constituents of the phospholipid bilayer in different microorganisms, so that their presence in food lipids has been linked to bacterial sources. Moreover, anteiso-FA are chiral due to the methyl substituent on the antepenultimate carbon atom. Little was known about the enantiomeric distribution of anteiso-FA in nature and especially in the phospholipids of food samples.