Preheat oven to 375°F. In a large bowl, combine dry ingredients and set aside. In another bowl, mash bananas and mix in mayonnaise. Add the wet ingredients to the dry and stir until incorporated. Pour into 2 greased loaf pans and bake for 35-40 minutes or until a toothpick inserted in the middle comes out clean. Cool in pan for at least 10 minutes before removing and slicing.