I'm going to park a few more links to articles about canine nutrition and selecting commercial dog foods below. I realize that most of them are behind paywalls, so if anyone wants details about a particular article, please feel free to PM me:
This article is about how commercial dog foods are made, and the rules and regulations for nutritional content:
Evaluating Pet Foods: How Confident Are You When You Recommend a Commercial Pet Food?
This is an article about commercial dog foods used in elimination diets, and how some of them are contaminated with other protein sources:
ELISA testing for common food antigens in four dry dog foods used in dietary elimination trials - Raditic - 2010 - Journal of Animal Physiology and Animal Nutrition - Wiley Online Library