This is similar to the scare over irradiated meat. Scientists since the 1960's have agreed that it is safe to use low-level radiation to kill all the microbes in food to increase the shelf life. The food doesn't retain any radioactivity; it's not different than food preserved in other ways. But when you are required to sell your normal hamburger as "irradiated hamburger", no one is going to buy it. The public sees a word similar to radiation and they are going to think that the meat contains radiation, even though it doesn't.
Specifically gamma rays. Gamma rays don't remain in the food after you fire them, so you can fire as many as you want at meat and it would never turn toxic.
