IMMUNOCHEMICAL DETECTION OF OXALIC-ACID MONOAMIDES THAT ARE FORMED DURING THE OXIDATIVE REACTION OF L-ASCORBIC-ACID AND PROTEINS

Covalent binding of L-ascorbic acid (AA) to proteins (protein ascorbyl ation) occurs during food processing and storage and in vivo. It contr ibutes, for example, to browning and various changes in the physical a nd physiological properties of proteins. Since oxalic acid monoalkylam ides (OMAs) are formed in high yields from AA and primary amines under oxidative conditions, it was determined if OMAs also represent an asc orbylation product of proteins. Therefore a polyclonal anti-OMA antibo dy was raised, and a high-titer antiserum was obtained which is specif ic against OMA. In a competitive ELISA total binding inhibition was ac hieved by ascorbylated protein, indicating that ascorbylation of prote ins leads to the formation of OMA. OMA is only formed under aerobic co nditions. Proteins, which were glycosylated with other carbohydrates s uch as glucose, did not show cross-reactivity, indicating that the ant iserum can be used to detect OMA as a specific marker for ascorbylatio n.