- Title
- Physicochemical effect of pH and antioxidants on mono- and triglutamate forms of 5-methyltetrahydrofolate, and evaluation of vitamin stability in human gastric juice: implications for folate bioavailability
- Creator
- Ng, Xiaowei; Lucock, Mark; Veysey, Martin
- Relation
- Food Chemistry Vol. 106, Issue 1, p. 200-210
- Publisher Link
- http://dx.doi.org/10.1016/j.foodchem.2007.05.057
- Publisher
- Elsevier
- Resource Type
- journal article
- Date
- 2008
- Description
- This report examines the physico-chemical properties of mono and triglutamate forms of 5-methyltetrahydrofolaten (5CH₃–H₄–PteGlun) in human gastric juice and under artificial conditions, typical of the upper gastrointestinal tract. Degradation of 5CH₃–H₄–PteGlun to 5-methyldihydrofolaten (5CH₃–5,6-H₂PteGlun) and on to the C₉–N₁₀ scission product p-aminobenzoylglutamate (P-ABG), and the salvage of 5CH₃–H₄–PteGlun from 5CH₃–5,6-H₂PteGlun was examined with emphasis on the influence of pH and ascorbic acid. At pH 3.5, physiological levels of ascorbic acid (50 μMol/l) salvage both 5CH₃–H₄PteGlu₁ and 5CH₃–H4PteGlu₃ from acid labile 5CH₃–5,6-H₂PteGlun and prevent loss of vitamin activity as indicated by P-ABGn formation. This process is less efficient at pH 7.0, although under such conditions 5CH₃–5,6-H₂PteGlun is rendered relatively stable. Ascorbic acid (50 μMol/l) reduces degradation of 5CH₃–H₄PteGlu₁ and 5CH₃–H₄PteGlu₃ at both pH 3.5 and 7.0. However, irrespective of ascorbic acid, 5CH₃–H₄PteGlu₁ and 5CH₃–H₄PteGlu₃ are both more stable at pH 3.5 than pH 7.0. There is a clear differential between mono- and polyglutamate stability, since, irrespective of pH or the presence of ascorbic acid, 5CH₃–H₄PteGlu₁ is inherently more stable than 5CH₃–H₄PteGlu₃. While ascorbic acid clearly stabilises mono- and triglutamate forms of methylfolate in human gastric juice, a factor in gastric juice removes any differential instability as seen in buffer solution. We speculate that this endogenous factor could be either a binding protein or some other antioxidant. These in vitro findings provide information that may be useful in evaluating the in vivo bioavailability of natural polyglutamate forms of the vitamin.
- Subject
- 5-methyltetrahydrofolate; folic acid; vitamin; dietary folic acid; vitamin C; vitamin bioavailability; vitamin absorption
- Identifier
- http://hdl.handle.net/1959.13/42768
- Identifier
- uon:4942
- Identifier
- ISSN:0308-8146
- Language
- eng
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