Triglyceride composition of bovine milk fat with elevated levels of linoleic acid

The effect of increasing the linoleic acid (18:2) content of milk fat on the composition and structure of the triglycerides (TG) was investigated. Protected sunflower seed supplement was added to the diet of a cow grazing on pasture, and the structure and composition of the milk fat compared with the milk fat from its monozygous twin which had been fed a control diet. The relative proportions of TG fractions of high, medium, and low molecular weight in the milk fat with elevated levels of 18:2 (15.5% 18:2) were 43.0, 19.5, and 37.5 moles %, respectively, compared with 36.1, 19.7, and 44.2 moles %, respectively in the milk fat from the cow fed the control diet. Separation of these three TG fractions of each milk fat into TG classes with different levels of unsaturation showed that the milk fat with elevated levels of 18:2 contained higher proportions of diene, triene, and tetraene TG and correspondingly lower proportions of saturated and, to a lesser extent, monoene TG. The saturated and monoene TG from the two milk fats had similar fatty acid compositions. However, the diene TG of the 18:2-rich milk fat included high proportions of the combination of 18:2 with two saturated fatty acids (FA) which are minor constituents of normal milk fats. Likewise, the triene TG reflected the presence of 18:2 in combination with 18:1 and a saturated FA.