Effect of domestic cooking methods on antioxidant capacity of fresh and frozen kale

The aim of this study was to evaluate the changes in the antioxidant capacity of fresh and frozen kale during domestic cooking methods (e.g., boiling, microwaving, and steaming). The antioxidant activities of the samples were measured using three in vitro assays (1,1-diphenyl-2-picrylhydrazyl assay, 2, 2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid assay, and ferric reducing antioxidant power assay). The steaming treatment was found to be the best cooking method to retain antioxidant compounds, followed by the microwaving and boiling treatments. The frozen uncooked samples exhibited a higher antioxidant capacity than the fresh, uncooked samples, indicating that the freezing process could enhance the antioxidant capacity of the kale.