Trans‐18:1 acid content and profile in human milk lipids. Critical survey of data in connection with analytical methods

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Abstract
This study presents an in‐depth, critical survey of the current knowledge about trans‐ 18:1 acid content and profile in human milk lipids. Emphasis is placed on the analytical methods employed to quantitate trans‐ 18:1 acids, most of which lead to imprecise quantitative data. It is demonstrated that data obtained by single gas‐liquid chromatography (GLC) on polar capillary columns are underestimates by 25–40%. Several experiments indicate that the total content of trans‐18:1 acids in human milk is directly related to the quantities ingested the previous day(s), provided no gross weight loss occurs during breast‐milk feeding. Equations have been proposed to describe this relationship, and apparently the percentage of trans‐18:1 isomers, relative to total fatty acids, is approximately three‐fourths the quantity (in g) ingested by lactating mothers. That is, the determination of the trans‐18:1 acid percentage in human milk is a convenient means to estimate trans‐18:1 acid consumption by corresponding populations. Adapted methods (i.e., silver‐ion thin‐layer chromatography, coupled with GLC on long polar capillary columns) allow accurate quantitation of most individual trans‐ 18:1 acids, more particularly of the trans‐Δ16 isomer. This determination, along with a knowledge of the distribution of individual isomers in ruminant fats and partially hydrogenated oils, is a convenient means to estimate the relative contribution of these two dietary sources to the distribution of individual trans‐18:1 isomers in human milk lipids. A comparison of human milk and infant formulas is made with regard to trans‐18:1 acid content and profile. Important differences are noted between data from European countries and from North America.