The colored varieties of corn - such as blue and purple - contain higher amounts of antioxidants than white or yellow corn. This is due to the anthocyanins which are present in their purple pigments. For example, at least one variety of purple corn has tested out with an ORAC of 10,800. For this reason, we often recommend incorporating the colored corns into your recipes whenever possible.
In the case of the Navajo blue corn mush recipe, we are actually surprised it scored as low as it did. That said, the cooking process and other ingredients used can greatly diminish the naturally occurring antioxidants in a food. The ash in particular would be a concern, since burnt items create a substance called acrylamide, which is classified as a suspected carcinogenic substance by the WHO.
USDA Database for the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 - Prepared by Nutrient Data Laboratory, Beltsville Human Nutrition Research Center (BHNRC), Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA) - May 2010