Rapid Method Using Two Microbial Enzymes for Detection of l -Abrine in Food as a Marker for the Toxic Protein Abrin

Abrin is a toxic protein produced by the ornamental plantAbrus precatorius , and it is of concern as a biothreat agent. The small coextracting moleculeN -methyl-l -tryptophan (l -abrine) is specific to members of the genusAbrus and thus can be used as a marker for the presence or ingestion of abrin. Current methods for the detection of abrin orl -abrine in foods and other matrices require complex sample preparation and expensive instrumentation. To develop a fast and portable method for the detection ofl -abrine in beverages and foods, theEscherichia coli proteinsN -methyltryptophan oxidase (MTOX) and tryptophanase were expressed and purified. The two enzymes jointly degradedl -abrine to products that included ammonia and indole, and colorimetric assays for the detection of those analytes in beverage and food samples were evaluated. An indole assay using a modified version of Ehrlich's/Kovac's reagent was more sensitive and less subject to negative interferences from components in the samples than the Berthelot ammonia assay. The two enzymes were added into food and beverage samples spiked withl -abrine, and indole was detected as a degradation product, with the visual lower detection limit being 2.5 to 10.0 μM (∼0.6 to 2.2 ppm)l -abrine in the samples tested. Results could be obtained in as little as 15 min. Sample preparation was limited to pH adjustment of some samples. Visual detection was found to be about as sensitive as detection with a spectrophotometer, especially in milk-based matrices.