That would be formaldehyde.
They also treat tomatoes with ethylene gas to "ripen" green tomatoes before their time so they keep on the shelf longer.
And that appetizing orangish-pink salmon filet? Dye.
The yellow in your grocery-store egg yolk? Dye in the chickens diet because factory chickens don't get enough sunlight to naturally turn the yolks yellow.
My family is seriously thinking about buying all our animal products from local farms, these things are just too nasty, but I'm not giving up meat. (please don't try to convince me otherwise, I've heard it all.)