Stability of labile folates is enhanced by binding to milk folate-binding protein

Folic acid is the parent of a number of derivatives that are vitamins, esse ntial for DNA and amino acid synthesis. Almost all naturally occurring fola tes are tetrahydro-folates, which are susceptible to oxidation in air, with loss of vitamin activity. Tetrahydrofolate (H4F) and 10-formyltetrahydrofo late are very labile, 5-methyltetrahydro-folate (5-CH3-H4F) is moderately l abile, while 5-formyltetrahydrofolate is quite stable. The predominant fola te present in milk is 5-CH3-H4F at a concentration of approximately 50 mu g /L. Folate binding protein (FBP) is present in bovine milk at a concentration i n excess of that required to bind all milk folates. The results of this pap er demonstrate that FBP stabilises tetrahydrofolates.