Trans fatty acids

Peer-reviewed | Manuscript received: April 09, 2018 | Revision accepted: : July 09, 2018

Origin, metabolism, health risks

Origin and nomenclature of trans fatty acids

Unsaturated fatty acids have double bonds mostly in cis-configuration, leading to a kink in the hydrocarbon chain. Trans fatty acids (TFA) on the contrary are unsaturated carboxylic acids with at least one double bond in trans configuration. In contrast to the cis isomer the hydrocarbon chain of a monounsaturated trans fatty acid is almost straight (♦ Figure 1).

Structure, melting point and other physical properties shift TFA in the direction of saturated fatty acids. For one TFA are generated during partial industrial hydrogenation of vegetable oils and, to a small extent, during oil refining [1]. This process turns liquid oils into semi-solid spreadable fats. Since the 1960s partially hydrogenated fats were a preferred alternative for saturated fats in the food industry. A high TFA content improves the functionality of a fat, i.e. texture and structure, thermal and oxidation stability and extends shelf life. There are also natural sources of TFA in fat from ruminants, i.e. milk fat and meat and products made from them, as enzymes of the rumen bacteria incompletely hydrogenate polyunsaturated fatty acids of the feed. Depending on the feeding regimen fat in cow’s milk contains 2–8% TFA [1, 2].

Abstract

Trans fatty acids (TFA) are generated both during partial industrial hydrogenation of oils and by incomplete microbial hydrogenation of polyunsaturated fatty acids in the rumen. Elaidic acid (t9-18:1), the trans isomer of oleic acid, is the major isomer in industrial sources of TFA. Some trans isomers of linoleic acid and of α-linolenic acid may also arise, depending on the vegetable oil used for hydrogenation and processing conditions. Vaccenic acid (t11-18:1) is the major trans isomer in ruminant fats. Elaidic acid and vaccenic acid differ in various biochemical activities. TFA show adverse effects on blood lipids, inflammation parameters and endothelial function. Epidemiological studies observed an increased risk of coronary heart diseases and total mortality with increasing intake of industrially generated TFA. Particularly fats for baking, roasting and deep-frying have or had a high content of TFA. Originally, margarine was an important source. Due to mandatory regulations and voluntary measures the TFA content of foods and thus TFA intake decreased markedly in many countries. This probably decreased health risks.

Keywords: elaidic acid, vaccenic acid, metabolism, health risks, intake, (governmental) regulations

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