Tzompa-Sosa D A, van Aken G A, van Hooijdonk A C M, van Valenberg H J F
Dairy Science and Technology Group, Food Quality and Design, Wageningen University, PO Box 17, 6700 AA, Wageningen, the Netherlands.
NIZO Food Research, PO Box 2, 6710 BA, Ede, the Netherlands.
J Dairy Sci. 2014 Jul;97(7):4542-51. doi: 10.3168/jds.2014-7937. Epub 2014 May 16.
Fatty acids (FA) are nonrandomly distributed within milk fat triacylglycerols (TAG). Moreover, the structure of milk fat TAG differs with feeding regimens. So far, nothing is known about the variation of milk fat TAG structure among individual cows. A deep understanding of the normal variation of TAG structures and the relationships between milk fat FA profile and its TAG structure could help to better control functional and compositional differences between milk fats from various sources and to increase the knowledge on milk fat synthesis. The focus of the present study was to determine the regiospecific TAG structure of individual samples of winter milk fat from Dutch Holstein-Friesian cows with a wide variation of FA profiles and with 2 diacylglycerol acyltransferase 1 (DGAT1) genotypes: DGAT1 K232A genotype AA and DGAT1 K232A genotype KK. From an initial set of 1,918 individual milk fat samples, 24 were selected. The selected samples had a wide range of FA composition and had either DGAT1 K232A genotype AA or KK. The structure analysis was done with a regiospecific approach. This analysis is based on the acyl degradation of TAG by a Grignard reagent and further isolation of sn-2 monoacylglycerols by thin-layer chromatography. An intra- and interpositional approach was used to study the structural variation. With the intrapositional approach, the amount of an FA at the secondary (sn-2) and primary (sn-1,3) positions was related to its total amount in the TAG. With the interpositional approach, the proportion of C8:0, C10:0, C14:1 cis-9, C16:1 cis-9, and C18:1 cis-9 at sn-2 was positively correlated with the amount of C16:0 in the triacylglycerol; in contrast, saturated C14:0, C16:0, and long-chain saturated FA (C14:0-C18:0) were negatively correlated. These observations suggest that the amount of long-chain saturated FA in TAG influences the positioning of other FA in the TAG. With an interpositional approach, the DGAT1 polymorphism had a significant effect on the proportional positioning of C16:0 at sn-2. These results provide a new direction to controlling functional and compositional differences between milk fats.
脂肪酸（FA）在乳脂肪三酰甘油（TAG）中呈非随机分布。此外，乳脂肪TAG的结构会因饲养方式而异。到目前为止，关于个体奶牛之间乳脂肪TAG结构的差异尚不清楚。深入了解TAG结构的正常变异以及乳脂肪FA谱与其TAG结构之间的关系，有助于更好地控制不同来源乳脂肪之间的功能和成分差异，并增加对乳脂肪合成的认识。本研究的重点是确定来自荷兰荷斯坦 - 弗里生奶牛的冬季乳脂肪个体样本的区域特异性TAG结构，这些样本具有广泛的FA谱变异以及两种二酰甘油酰基转移酶1（DGAT1）基因型：DGAT1 K232A基因型AA和DGAT1 K232A基因型KK。从最初的1918个个体乳脂肪样本中，选择了24个。所选样本具有广泛的FA组成，并且具有DGAT1 K232A基因型AA或KK。结构分析采用区域特异性方法进行。该分析基于格氏试剂对TAG的酰基降解以及通过薄层色谱进一步分离sn-2单酰甘油。采用了内部和位置间方法来研究结构变异。通过内部位置方法，FA在二级（sn-2）和一级（sn-1,3）位置的含量与其在TAG中的总量相关。通过位置间方法，sn-2位的C8:0、C10:0、C14:1顺式-9、C16:1顺式-9和C18:1顺式-9的比例与三酰甘油中C16:0的含量呈正相关；相反，饱和的C14:0、C16:0和长链饱和FA（C14:0 - C18:0）呈负相关。这些观察结果表明，TAG中长链饱和FA的含量会影响其他FA在TAG中的定位。通过位置间方法，DGAT1多态性对sn-2位C16:0的比例定位有显著影响。这些结果为控制乳脂肪之间的功能和成分差异提供了新的方向。
