Most restaurants - fast food as well as sit-down - typically use frozen hamburger patties which are defrosted and then fried, which is the type of patty reflected in this test. However even when a frozen (uncooked) hamburger was tested, its value was only 9% higher for one brand and actually 64% lower for another brand. In other words, a hamburger has very little antioxidants, even before it is exposed to heat from cooking.
Research Support, Non-U.S. Gov't: Carlsen MH, Halvorsen BL, Holte K, et al. Nutrition Journal NIH Jan 2010