ARTICLE
TITLE

Trans fatty acids and their role in the milk of dairy cows

SUMMARY

Lipids obtained from dairy products are an important part of the human diet in many countries. Approximately 75% of the total consumption of fat from ruminant animals comes from bovine milk fat. Trans fatty acids (tFA) are produced during biohydrogenation of mono- and poly-unsaturated FA in the rumen. They are mixtures of positional and geometrical isomers that are incorporated into the milk fat of lactating cows. The most important sources of tFA in the human diet are partially hydrogenated vegetable oils and ruminant milk and meat products. Ruminant-derived lipids often contain 1-8% of total fatty acids as tFA, which are predominantly 18:1 isomers. The most common FA in ruminant fat is vaccenic acid (18:1 trans-11) (VA), accounting for 60-80% of total tFA. Unlike other tFA, VA can be converted to rumenic acid (RA) through the action of stearoyl coenzyme-A desaturase. Today, consumers are becoming aware of the relationship between dietary fat, health maintenance, and disease prevention. These concerns have increased the need to investigate the metabolic fate and bioactivity of dietary FA. By altering the nutrition of cows, farmers can markedly and rapidly modulate the FA composition of milk FA. The largest changes can be obtained either by feeding animals high-quality forage, particularly fresh pasture, or by adding plant or marine oils to the diet. Given that economic factors define future profits for farmers, diet manipulation may be the most practical and appropriate approach to change milk’s FA composition. La grasa de productos lácteos es muy importante en la dieta humana en muchos países. Aproximadamente, el 75% del consumo total de grasa de productos de rumiantes proviene de la grasa láctea. Los ácidos grasos trans (AGT) son producidos durante la hidrogenación ruminal de AG poliinsaturados. Son una mezcla de isómeros que son incorporados en la grasa láctea de vacas lactantes. La principal fuente de AGT de la dieta humana proviene de los aceites vegetales parcialmente hidrogenados y de la leche y carne de rumiantes. Usualmente los lípidos de la leche y carne de rumiantes contienen entre 1 a 8% de AGT del total de AG presentes, y en su mayoría compuestos por isómeros 18:1. El AGT más común en la grasa de rumiantes es el vaccénico (18:1 trans-11), el cual representa entre un 60 a 80% del total de AGT. A diferencia de los AGT de los aceites vegetales parcialmente hidrogenados, los AGT de rumiantes (ácido vaccénico) pueden ser convertidos en ácido ruménico a través de la enzima estearoil coenzima-A desaturasa. Actualmente, los consumidores están conscientes de la relación entre la grasa de la dieta, la salud y la prevención de enfermedades. Estas preocupaciones han motivado la necesidad de investigar el destino metabólico y la bioactividad de los AG de la dieta. Mediante la manipulación de la nutrición de la vaca lechera, los productores pueden modular y alterar la composición de la grasa láctea. Los cambios más grandes se pueden observar mediante la calidad del forraje de la dieta (pastos) o mediante la utilización de suplementos vegetales o marinos en la dieta. Dado que la factibilidad económica está definida por las ganancias de los productores, la manipulación de la dieta de la vaca lechera es la alternativa más factible y práctica para modificar la composición de la grasa láctea. 

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