Thermal Stability of Ricin in Orange and Apple Juices

Ricin is a potent protein toxin that could be exploited for bioterrorism. Although ricin may be detoxified using heat, inactivation conditions in foods are not well characterized. Two brands of pulp-free orange juice and 2 brands of single-strength apple juice (one clarified and the other unclarified) containing 100 mu g/mL added ricin were heated at 60 to 90 degrees C for up to 2 h. With increasing heating times and temperatures the heat-treated juices exhibited decreasing detectability of ricin by enzyme-linked immunosorbent assay (ELISA) and cytotoxicity to cultured cells. Z-values for ricin inactivation in orange juices were 14.4 +/- 0.8 degrees C and 17 +/- 4 degrees C using cytotoxicity assays, compared to 13.4 +/- 1.5 degrees C and 14 +/- 2 degrees C determined by ELISA. Although insignificant differences were apparent for z-values measured for the 2 orange juice brands, significant differences were found in the z-values for the 2 brands of apple juice. The z-values for ricin inactivation in the clarified and unclarified apple juices were 21 +/- 4 degrees C and 9.5 +/- 1.1 degrees C, determined by cytotoxicity assays, and 20 +/- 2 degrees C and 11.6 +/- 0.7 degrees C, respectively, using ELISA. Overall, there were no significant differences between results measured with ELISA and cytotoxicity assays. Ricin stability in orange juice and buffer was evaluated at 25 degrees C. Half-lives of 10 +/- 3 d and 4.9 +/- 0.4 d, respectively, indicated that active ricin in juice could reach consumers. These results indicate that ricin in apple and orange juices can remain toxic under some processing and product storage conditions. Practical Application: Ricin is a potent toxin that is abundant in castor beans and is present in the castor bean mash by-product after cold-press extraction of castor oil. U. S. Health and Human Services recognizes that ricin could be used for bioterrorism. This study reports the stability of ricin in apple and orange fruit juices at temperatures ranging from 60 to 90 degrees C (140 to 194 degrees F).