Evaluation of an in vitro bioassay for the detection of purified ricin and castor bean in beverages and liquid food matrices

The potential use of ricin as a biological weapon in food highlights the necessity for the development of food-specific detection methods. Current methods for the detection of ricin consist of various immunoassays, which detect only one subunit of the ricin toxin and therefore may not be indicative of a biologically active molecule. An in vivo assay, such as a mouse bioassay, can indicate the biological activity of the toxin; however, this method is not feasible for laboratories that do not have animal testing facilities. The purpose of this study was to develop an in vitro assay for the detection of biologically active ricin in beverages and liquid foods. Acidic and high-protein beverages were spiked with either purified ricin or ground castor beans and added to cultured human Jurkat cells. After an overnight incubation, the supernatant was tested for lactate dehydrogenase (LDH) activity with a colorimetric assay. LDH was released from the cytosol upon cell damage and was positively correlated with cell death. Ricin was detectable in all the matrices tested, with a sensitivity of 10 to 100 pg/ml. Biologically active ricin was detectable in all the matrices incubated with ground castor bean material. This method provides a confirmatory way to detect biologically active ricin that can be utilized by laboratories lacking animal facilities.