I am of the mind that preservatives in food in general are a bad thing, we and our pets are designed to eat simple items, the more complex the product tends to be (for example the sugar from a piece of fruit vs. sugar contained in a soda pop) these break down in the body and leave different items behind, trace amounts of chemicals that absorb into your dog’s blood stream or collect in the body.  I think that with the whole organic and hormone free movement, we can get to a place where the food we and our pets eat is not packed full of so many fillers and garbage, and I think as that happens the incidence of dog food allergies and human food allergies will both go down in number as a result.