Kraft Jana, Collomb Marius, Möckel Peter, Sieber Robert, Jahreis Gerhard
University of Jena, Institute of Nutrition, D-07743 Jena, Germany,
Lipids. 2003 Jun;38(6):657-64. doi: 10.1007/s11745-003-1111-z.
The uniqueness of ruminant milk lipids is based on their high concentration of CLA. Maximal CLA concentrations in milk lipids require optimal conditions of ruminal fermentation and substrate availability, conditions like those present in pasture-fed cows. Our previous work showed that farm management (indoor feeding vs. pasture feeding) markedly influenced the CLA concentration. In this study, the objective was to evaluate the influence of the farm management system as dependent on different locations. Milk samples from different locations (Thuringia and the Alps, representing diverse altitudes) were collected during the summer months and analyzed for FA profile and CLA isomer distribution. The proportion of PUFA and total CLA in milk fat was significantly lower in milk from indoor cows compared with the pasture cows in the Alps. The trans-11 18:1 in milk fat of Alpine cows was elevated, in contrast to lower values for trans-10 18:1. Milk from cows grazing pasture in the Alps was higher in EPA and lower in arachidonic acid than milk from indoor-fed cows. The proportion of cis,trans/trans,cis isomers of CLA was 10 times higher from the indoor cows than from the Alpine cows. In addition to the major isomer cis-9,trans-11, this difference also occurred for the trans-11,cis-13 isomer, which represented more than a fourth of the total CLA present in milk fat. This is the first report showing a special isomer distribution in the milk fat of cows living under very natural conditions. We hypothesize that the CLA isomer trans-11,cis-13 is formed in large quantity as a result of grazing mountain pasture, which is rich in alpha-linolenic acid.
反刍动物乳脂的独特性在于其共轭亚油酸（CLA）的高浓度。乳脂中CLA的最大浓度需要瘤胃发酵和底物可用性的最佳条件，类似于放牧奶牛所具备的条件。我们之前的研究表明，农场管理方式（室内饲养与放牧）对CLA浓度有显著影响。在本研究中，目的是评估依赖于不同地点的农场管理系统的影响。在夏季收集来自不同地点（图林根州和阿尔卑斯山，代表不同海拔）的牛奶样本，并分析其脂肪酸谱和CLA异构体分布。与阿尔卑斯山放牧奶牛的牛奶相比，室内饲养奶牛的牛奶中多不饱和脂肪酸（PUFA）和总CLA的比例显著更低。阿尔卑斯山奶牛乳脂中的反式-11 18:1升高，而反式-10 18:1的值较低。与室内饲养奶牛的牛奶相比，阿尔卑斯山放牧奶牛的牛奶中二十碳五烯酸（EPA）含量更高，花生四烯酸含量更低。室内饲养奶牛的CLA顺式/反式/反式/顺式异构体比例比阿尔卑斯山奶牛高10倍。除了主要异构体顺式-9，反式-11外，反式-11，顺式-13异构体也存在这种差异，该异构体占乳脂中总CLA的四分之一以上。这是第一份显示生活在非常自然条件下的奶牛乳脂中特殊异构体分布的报告。我们推测，CLA异构体反式-11，顺式-13大量形成是由于放牧富含α-亚麻酸的山地牧场所致。
