In a large mixing bowl, using an electric mixer, beat together the cake mix, egg whites, vegetable oil, and 1 1/2 cups of pureed strawberries for 2 minutes. Scrape down the sides of bowl to make sure all the batter is well incorporated. Using a mini ice-cream scoop, fill the muffin tins about 3/4 of the way to the top. Bake until the tops are golden and a toothpick inserted in the center comes out clean, about 8 to 10 minutes. Remove the tins from the oven cool slightly before removing the muffins. Cool completely on a wire rack before frosting.