Lawson R E, Moss A R, Givens D I
ADAS Bridgets Dairy Research Centre, Martyr Worthy, Winchester SO21 1AP, UK.
Nutr Res Rev. 2001 Jun;14(1):153-72. doi: 10.1079/NRR200121.
Health benefits for man have been associated with conjugated linoleic acid (CLA) and dairy products are highlighted as offering the best opportunity to increase CLA consumption. CLA is synthesised in the rumen as an intermediate in the biohydrogenation of linoleic acid to stearic acid. The supplies of both intermediates and endproducts of biohydrogenation are affected by the substrate supply and extent of biohydrogenation, thus influencing the CLA content of milk from ruminants. The majority of CLA is present in the rumen in the form of the cis-9,trans-11 isomer. The transfer efficiency of CLA to milk fat is affected by the presence of different isomers of CLA. Ruminant mammary and adipose cells are able to synthesise cis-9,trans-11-CLA from trans-11-18:1 (vaccenic acid) by the action of the Delta9-desaturase enzyme. Plant oils are high in both linoleic and linolenic acids, which results in increased CLA production in the rumen and in the mammary gland. The CLA content of milk increases when cows are offered grazed grass. Many published studies examining the CLA concentration of processed milk were confounded by variations in the concentration of CLA in the raw milk.
共轭亚油酸（CLA）对人体健康有益，乳制品被视为增加CLA摄入量的最佳途径。CLA是在瘤胃中由亚油酸生物氢化生成硬脂酸的中间产物。生物氢化的中间产物和终产物的供应受底物供应和生物氢化程度的影响，进而影响反刍动物乳中的CLA含量。大部分CLA以顺-9，反-11异构体的形式存在于瘤胃中。CLA不同异构体的存在会影响其向乳脂肪的转化效率。反刍动物的乳腺和脂肪细胞能够通过Δ9-去饱和酶的作用将反-11-18:1（vaccenic acid）合成顺-9，反-11-CLA。植物油富含亚油酸和亚麻酸，这会导致瘤胃和乳腺中CLA产量增加。给奶牛喂饲青草时，乳中的CLA含量会增加。许多已发表的研究在检测加工乳中CLA浓度时，因原料乳中CLA浓度的变化而受到干扰。
