Institute of Food Chemistry, University of Hohenheim, Garbenstrasse 28, D-70599 Stuttgart, Germany.
J Agric Food Chem. 2010 Jan 27;58(2):707-12. doi: 10.1021/jf9034805.
Branched chain fatty acids (iso- and anteiso-fatty acids) are common minor compounds of the lipids found in dairy products and fish (<1-3%) and major fatty acids of Gram-positive bacteria. Their presence in food has been associated with bacterial sources. Bacterial lipids usually consist of polar lipids and virtually no triacylglycerides while food lipids are predominantly composed of triacylglycerides. In this study, we examined the difference in the iso- or anteiso-fatty acid content and composition of neutral and polar lipids in fish and cheese samples. Neutral lipids (triacylglycerides) were separated from the polar lipids (phospholipids) by means of solid-phase extraction (SPE). Deuterium-labeled internal standards were used to verify the successful performance of the accelerated solvent extraction and particularly the SPE. The separated lipid fractions were transformed into their corresponding fatty acid methyl esters, and the concentrations of seven iso- and anteiso-fatty acids were determined by means of gas chromatography coupled to electron ionization mass spectrometry operated in the selected ion monitoring mode (GC/EI-MS-SIM). No coelutions of branched chain fatty acids with other fatty acids were obtained on the medium polar column used for quantification. The branched chain fatty acid content of 17 cheese and 7 fish samples ranged between 0.2% and 1.9% in polar lipids and between 0.1% and 1.7% in neutral lipids. The concentration of total branched chain fatty acids in fish was 2-10 times lower than that found in cheeses, and the relative distribution of iso-17:0 and iso-15:0 increased compared to their anteiso homologues. While branched chain fatty acids in polar lipids of cheese constituted only approximately 1% of the content in total lipids, their contribution in fish was significantly higher (6% to >30%).
支链脂肪酸（异和反脂肪酸）是乳制品和鱼类中脂质的常见少量化合物（<1-3%），也是革兰氏阳性菌的主要脂肪酸。它们在食物中的存在与细菌来源有关。细菌脂质通常由极性脂质组成，几乎不含三酰基甘油，而食物脂质主要由三酰基甘油组成。在这项研究中，我们研究了鱼和奶酪样品中中性和极性脂质的异或反脂肪酸含量和组成的差异。通过固相萃取（SPE）将中性脂质（三酰基甘油）与极性脂质（磷脂）分离。氘标记的内标用于验证加速溶剂萃取和特别是 SPE 的成功性能。分离的脂质部分转化为相应的脂肪酸甲酯，并通过气相色谱与电子电离质谱在选择离子监测模式下（GC/EI-MS-SIM）测定七种异或反脂肪酸的浓度。在所使用的中等极性柱上，没有支链脂肪酸与其他脂肪酸的共洗脱。17 个奶酪和 7 个鱼样品中支链脂肪酸在极性脂质中的含量在 0.2%到 1.9%之间，在中性脂质中的含量在 0.1%到 1.7%之间。鱼中总支链脂肪酸的浓度比奶酪低 2-10 倍，异-17:0 和异-15:0 的相对分布与它们的反同系物相比有所增加。虽然奶酪中极性脂质中的支链脂肪酸仅占总脂质含量的约 1%，但在鱼中的贡献明显更高（6%至>30%）。
