In a large bowl, combine the dry ingredients. Add oil and orange juice; beat until smooth. In another bowl, beat egg whites until stiff peaks form. Fold into orange juice mixture. Coat a 9x5-in. loaf pan with cooking spray; dust with flour. Pour batter into pan.
Bake at 350° for 1 hour or until a toothpick inserted in the center comes out clean. Cool for 10 minutes before removing from pan to wire rack to cool completely. Dust with confectioners' sugar.