Determination of the Maillard product oxalic acidmonolysinylamide (OMA) in heated milk products by ELISA.

Oxalic acid monolysinylamide (OMA), a Maillard product which had initially been identified as a reaction product of L-ascorbic acid, was formed, dependent on the reaction conditions, also from other carbohydrate sources. At elevated temperatures and in the presence of oxygen, the reaction of lactose with proteins resulted in the formation of relatively high amounts of OMA. Using a polyclonal antibody, which bound with high specificity and affinity to OMA-modified proteins, a competitive enzyme linked immunosorbent assay (ELISA) was developed to measure OMA formation in heat-treated milk products. The assay performance was characterized for OMA-modified beta-lactoglobulin diluted in buffer or pasteurized milk. For the latter, the least detectable dose was determined as 1.4 ng/ml with a linear range for quantification between 2 ng/ml and 200 ng/ml. For some samples intra- and interassay variation were determined. The ELISA was used to measure OMA-formation in heated milk and commercially available infant formula.