2.3.3. Vitamin A Concentration

The Vit A in colostrum was measured using high-performance liquid chromatography (HPLC) with a UV detector as described previously [13]. In brief, after the samples were thawed, the fat was saponified with alcoholic potassium hydroxide solution. The Vit A was extracted from unsaponifiable portions with n-hexane and evaporated under nitrogen. The residue was dissolved in methanol and injected into the reverse phase C18 µ-Bondapak (3.9 × 300 mm) column (Water Corp., Milford, MA, USA). The mobile phase consisted of methanol (RCI Labscan Ltd., Bangkok, Thailand) set at the flow rate of 1 mm/min and Vit A was detected at 340 nm using the HPLC system (HPLC-Shimadzu, Kyoto, Japan). The recovery of the added standard at the level 5–20 ppm was 99.5% and a standard deviation of 3.78.