The Degradation of L-Ascorbic Acid in Neutral Solutions Containing Oxygen

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Abstract
The stability of L-ascorbic acid was examined by incubating it alone and in the presence of α-N-formyl-L-Lysine (NFL) at pH 7.0 (0.1 M phosphate buffer) in the presence of oxygen, a metal ion chelator, and in both the presence and absence of sodium cyanoborohydride. Among the large number of degradation products produced, threonic, oxalic, glyceric and glyoxylic acids, as well as threose were all identified by GLC-MS. Decarboxylation is also a feature of the degradation, with approximately 30% of the ascorbic acid undergoing degradation via this pathway. In the presence of cyanoborohydride and NFL, ε-N-carboxymethyl-L-lysine (CML) was detected as a reaction product as well. Using GLC-MS as the detection method and ascorbic acid-1-13C as the reactant, only glyoxylic acid and CML were found to contain a 13C label, indicating that, of the compounds identified above, only these latter two contain C-1 of ascorbic acid.