Preheat oven to 350ºF.  Lightly coat a  8x2x2 baking pan with nonstick cooking spray. In a large bowl, combine flours, brown sugar, cinnamon, ginger, baking powder and baking soda. In a small bowl, combine buttermilk, applesauce, molasses and egg whites; add to flour mixture. Beat until combined. Pour into baking pan and bake 30 to 35 minutes. Cool for 10 minutes, cut cake into nine squares and dust with powdered sugar.