Trans fatty acids are produced when oils and fats containing unsaturated fatty acids are hydrogenated in the presence of a catalyst. Hydrogenation primarily increases the melting range of the unsaturated fats and thereby enables their incorporation into many solid fat formulations. When an unsaturated fat or oil is fully hydrogenated, all the unsaturated fatty acids are converted into their saturated analogues. Since the unsaturation in most vegetable oils is largely in the 18-carbon fatty acids, namely, oleic (18:1 n-9), linoleic (18:2 n-6) and linolenic (18:3 n-3), full hydrogenation of such oils would result in a stearic acid (18:0), high melting block of fat. Partial hydrogenation, usually in the presence of nickel catalysts, results in the formation of trans fatty acids that are the geometrical isomers of the unsaturated fatty acids, containing at least one double bond in the trans configuration. This trans double bond configuration impacts the physical properties of the fatty acid with a potential for reducing the fluidity of the fatty acid thereby increasing its melting point. Thus, partial hydrogenation of liquid oils has been the tool of choice to enable their use in solid fats, especially margarine formulations. Partial hydrogenation actually results in both cis and trans fatty acids anywhere between carbon 4 and carbon 18 of the fatty acid molecule with elaidic acid (9trans 18:1) being a major isomer and smaller amounts of numerous other trans isomers occurring concurrently. Upwards of 20 different cis and trans geometrical isomers have been recorded following partial hydrogenation of vegetable oils. Small amounts of trans fatty acids occur naturally in dairy fat (butter) and meat as a result of bio-hydrogenation in the fore stomach of ruminants.
Keywords: MPOB PUBLICATIONS, NUTRITION, HEALTH, PALM OIL, DIETARY FATS, TRANS FATTY ACIDS