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Covalent binding of l-ascorbic acid (AA) to proteins (protein ascorbylation) occurs during food processing and storage and in vivo. It contributes, for example, to browning and various changes in the physical and physiological properties of proteins. Since oxalic acid monoalkylamides (OMAs) are formed in high yields from AA and primary amines under oxidative conditions, it was determined if OMAs also represent an ascorbylation product of proteins. Therefore a polyclonal anti-OMA antibody was raised, and a high-titer antiserum was obtained which is specific against OMA. In a competitive ELISA total binding inhibition was achieved by ascorbylated protein, indicating that ascorbylation of proteins leads to the formation of OMA. OMA is only formed under aerobic conditions. Proteins, which were glycosylated with other carbohydrates such as glucose, did not show cross-reactivity, indicating that the antiserum can be used to detect OMA as a specific marker for ascorbylation. Keywords: l-Ascorbic acid; ascorbylation; immunochemical detection; Maillard reaction; OMA protein; oxalic acid monoalkylamide

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