GEOMETRICAL-ISOMERS OF ESSENTIAL FATTY-ACIDS IN LIQUID INFANT FORMULAS

Lipid was extracted from liquid infant formulas using diethyl ether-ethanol-hexane. Fatty acid methyl esters were prepared using boron trifluoride catalyzed transesterification. Fatty acid methyl esters were separated by gas-liquid chromatography using a CPSil88 cyanopropylsilicone column. Fatty acids were identified by comparison of retention times with standards and calculated equivalent chain lengths with geometrical isomers of 18:2w6 and 18:3w3 prepared by elaidinization of linseed oil. The levels of linoleic and linolenic acid in all but three samples exceeded 20% and 3% of total fatty acids, respectively. Trans geometrical isomers of linoleic (18:2w6) and linolenic (18:3w3) acids were present in all formulas. The amount of the 18:3 tcc isomer was higher than cct or tct+ctt. Trace amounts of etc were found. 18:2 tt and 18:3 ttt were not detected. Levels of total trans fatty acids ranged from 0.15% to 1.26%. The isomerization of linoleic acid ranged from 0.17% to 2.4%. Isomerization of linolenic acid ranged from 2.6% to 23.5%. Infant formulas have substantial variations in 18:3w3 isomerization. The most highly isomerized formulas would provide almost one quarter of the 18:3 as isomers. Infants could receive substantial relative amounts of linolenic acid isomers from typical liquid infant formulas.