Many packaged goods undergo transition metal-catalyzed oxidative spoilage. Recently, a nonmigratory photocurable metal-chelating coating was developed as an innovative active packaging approach to control oxidation of foods. In the present study, we investigate the influence of competing ions and increasing viscosity on the iron-chelating capacity and antioxidant efficacy of this coating in a model complex food system. The addition of calcium and magnesium causes a decrease in iron chelating capacity; however, 61% chelating capacity of materials was retained when 0.8 M sodium was present. Materials retained iron-chelating capacity even in solutions of 2700 cP, similar to the viscosity of salad dressing. Additionally, metal-chelating films significantly delayed transition metal-catalyzed ascorbic acid degradation, even in the presence of competing ions and at increased viscosity. These results suggest that metal-chelating active packaging coatings may present a new technological approach to addressing consumer demands for reduced additive use while controlling food spoilage and waste.