Isolation, Quantification, and Biosynthetic Origin of Orotic Acid in Milk

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Abstract
The most frequently used methods for estimating orotic acid in milk are variations of a colorimetric procedure. The assay involves the isolation of orotic acid by dialysis and anion exchange and silicic acid chromatography. This is followed by the silylation of the purified orotic acid and its quantification by GLC. This technique was compared with a colorimetric method on various milk samples and the results by the 2 methods were similar. Both confirmed the high orotic acid content of bovine mik. Orotic acid was less in commercial cultured buttermilk and goat milk and not detectable in human milk. The ability to isolate orotic acid in essentially pure form made it possible to study its biosynthesis in vivo. Intramammary infusion of 14C uniformly labeled aspartic acid, a precursor, confirmed in vitro studies indicating that orotic acid in milk originates almost exclusively in mammary cells.