Dredge an apple piece in the flour mixture, coating it well on all sides but letting any excess fall back into the bowl. Dip the wedge in the egg-white mixture, coating it all over and allowing any excess to fall back into the bowl. Set the wedge in the graham cracker crumbs and press firmly but gently, turning the wedge to get a full coating on all sides, even the edges. Coat generously with nonstick spray and set aside. Continue dredging and dipping the remaining apple wedges.