Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.13/42768

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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
Author/Creator
Ng, Xiaowei;  Lucock, Mark;  Veysey, Martin
Institution
The University of Newcastle. Faculty of Faculty of Science & Information Technology, School of Environmental and Life Sciences
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.
Relation
Food Chemistry Vol. 106, Issue 1, p. 200-210
Publisher Link
http://dx.doi.org/10.1016/j.foodchem.2007.05.057
Date
2008
Publisher
Elsevier
Keyword(s)
5-methyltetrahydrofolate;  folic acid;  vitamin;  dietary folic acid;  vitamin C;  vitamin bioavailability;  vitamin absorption
Resource Type
journal article
Identifier
http://hdl.handle.net/1959.13/42768
Identifier
ISSN:0308-8146
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Subject
"Food Chemistry"
 
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