Richter Eva Katharina, Spangenberg Jorge E, Klevenhusen Fenja, Soliva Carla R, Kreuzer Michael, Leiber Florian
Institute of Agricultural Sciences, ETH Zurich, Universitaetstrasse 2, 8092, Zurich, Switzerland.
Lipids. 2012 Feb;47(2):161-9. doi: 10.1007/s11745-011-3599-0. Epub 2011 Aug 12.
This study explores the potential use of stable carbon isotope ratios (δ(13)C) of single fatty acids (FA) as tracers for the transformation of FA from diet to milk, with focus on the metabolic origin of c9,t11-18:2. For this purpose, dairy cows were fed diets based exclusively on C(3) and C(4) plants. The FA in milk and feed were fractionated by silver-ion thin-layer chromatography and analyzed for their δ(13)C values. Mean δ(13)C values of FA from C(3) milk were lower compared to those from C(4) milk (-30.1‰ vs. -24.9‰, respectively). In both groups the most negative δ(13)C values of all FA analyzed were measured for c9,t11-18:2 (C(3) milk = -37.0 ± 2.7‰; C(4) milk -31.4 ± 1.4‰). Compared to the dietary precursors 18:2n-6 and 18:3n-3, no significant (13)C-depletion was measured in t11-18:1. This suggests that the δ(13)C-change in c9,t11-18:2 did not originate from the microbial biohydrogenation in the rumen, but most probably from endogenous desaturation of t11-18:1. It appears that the natural δ(13)C differences in some dietary FA are at least partly preserved in milk FA. Therefore, carbon isotope analyses of individual FA could be useful for studying metabolic transformation processes in ruminants.
本研究探讨了单个脂肪酸（FA）的稳定碳同位素比率（δ(13)C）作为追踪脂肪酸从日粮向牛奶转化的潜在用途，重点关注共轭亚油酸（c9,t11-18:2）的代谢来源。为此，给奶牛仅饲喂基于C(3)和C(4)植物的日粮。通过银离子薄层色谱法分离牛奶和饲料中的脂肪酸，并分析其δ(13)C值。与来自C(4)牛奶的脂肪酸相比，来自C(3)牛奶的脂肪酸的平均δ(13)C值更低（分别为-30.1‰和-24.9‰）。在两组中，所分析的所有脂肪酸中，c9,t11-18:2的δ(13)C值最负（C(3)牛奶=-37.0±2.7‰；C(4)牛奶=-31.4±1.4‰）。与日粮前体18:2n-6和18:3n-3相比，在t11-18:1中未检测到显著的(13)C贫化。这表明c9,t11-18:2中δ(13)C的变化并非源于瘤胃中的微生物生物氢化作用，而很可能源于t11-18:1的内源性去饱和作用。看来某些日粮脂肪酸中天然的δ(13)C差异至少部分保留在牛奶脂肪酸中。因此，对单个脂肪酸进行碳同位素分析可能有助于研究反刍动物的代谢转化过程。
