I have a recipe for an apple cake that calls for all purpose flour. I was wondering if a whole wheat pastry flour, like the one made by Arrowhead Mills, can be substituted for all of the white flour or just some of it. I know when using a hard wheat whole wheat flour, only half can be whole wheat, but this pastry flour seems different. If all whole wheat pastry flour can be used, are any other changes needed in the recipe, such as more liquid, fat, etc.? Thanks!