Select fame

The method for analysing the fatty acid profiles is described elsewhere [25 (link),26 (link)].
The methyl esters were determined using a Hewlett-Packard 5890 series II gas chromatograph, a fused silica capillary column Select FAME (100 m × 0.25 mm, 0.25 μm film thickness) (Varian, Bellafonte, PA, USA), and a flame ionisation detector. Quantification was achieved according to Commission Regulation (ECC) No 2568/91 [3 ]. Values are the average of two determinations per sample.

Milk fat was extracted with petroleum ether from freeze-dried milk samples. FAs in extracted fat were re-esterified to their methyl esters with a methanolic solution of potassium hydroxide. Briefly, 0.2 mL 2M KOH in methanol was added to 1 mL petroleum ether extract, and the sample was left for 2 min in a water bath at 60 °C. The sample was then neutralized with 0.4 mL 1M HCl in methanol, diluted with 1 mL petroleum ether, and used for GC analysis. Methyl esters of FAs were determined by GC method (Table 1) using a Varian 3800 apparatus (Varian Techtron, Palo Alto, CA, USA) with FID (for quantitative) and 4000 MS detector (Varian; for qualitative analysis) on a capillary column 50 m × 0.25 mm and 0.25-µm film thickness (SELECT FAME; Varian).
FA proportion is specified by counting peak area proportion to the total peak area of all determined FAs. Weight percentage data were calculated from the area data by means of the relative factors by standards FAME mix (Supelco, Darmstadt, Germany). A total of 56 FAs were determined by the GC method.