what is causing this

My son is almost 4 and is allergic to casein (milk protein) we have switched him to soy milks and casein free products.  We purchased some "Tofutti" brand dairy free (and casein free) pizzas for him.   I have noticed the last 2 times I have given it to him that minutes after eating he develops a rash on each side of his mouth.  They first time the rash on each side was round and bright red.  This time one side is rounded and the other is more of a rectangle.  The rash is very red and had a very obvious warmth when you touch it.  The last time it seemed to be flat but this time noticed one or two raised spots.  He does not have it anywhere else.  It does not itch him.  He does not have this kind of reaction from the casein in products...and this one is casein free.  These are the ingredients in the product.

Wheat flour (unbleached), water, Dairy-Free Better than mozzarella cheese, partially hydrogenated soybean oil, tofu, soy protein, crushed tomatoes, potato flakes, maltodextrin, corn starch, vinegar, adipic acid, sodium phosphate, soy lecithin, natural flavors, sugar, salt, yeast, spices, garlic powder.

I believe he has had all of these before with the exception of Maltodextrin and Adipic acid.  Is anyone familiar with either of these?  

[Pum]

I answered you on the allergy forum.