I’ve had some interesting e-mail on the subject, which I thought I’d address here for the curious. One person mentioned the possibility of ricin dissolved in DMSO. I have to say that that’s a nasty thought, because DMSO certainly does increase skin permeability. But I don’t know how soluble a large peptide like this would be – even in DMSO, which is generally a solvent of last resort in chemistry. And even if you could get some of the protein in there, odds are excellent that it would denature, change its conformation as it went into solution. Most enzymes shift around so much going into solvents like DMSO that they lose their activity completely. Not all of them, though – but I would put ricin in the category of unlikely to survive the transition. It has an important disulfide bond that would probably be labile to oxidation on storage in DMSO as well.
Others have mentioned food adulteration. If my guesstimate of a gram or two for lethality is right, a big problem would be that the stuff would probably alter the taste of whatever you added it to. I certainly have no idea of what ricin tastes like – and I’m not about to find out, because sublethal doses are still pretty unpleasant. But it’s unlikely to be unnoticable. The heat of cooking is an even better denaturant than any organic solvent, usually, but ricin is said to be unusually heat-stable. That’s not saying much in protein chemistry, though – boiling water is considered insane heat in the protein world. It’s not likely to be a useful agent in someone’s french fries; you’ll just have to count on the acrylamide.