To prepare streusel: In a small bowl, combine flour, brown sugar, cinnamon, and salt. Stir in walnuts. Drizzle apple juice concentrate and oil over dry ingredients and rub with your fingers until crumbly. Set aside.
Preheat oven to 350*. Coat 2 - 8 1/2x4 1/2 loaf pans with cooking spray.
To prepare bread: In a large bowl, beat egg whites with an electric mixer on low speed until foamy. Add cream of tartar, increase speed to medium-high and beat until soft peaks form. Gradually add 1/2 cup sugar, beating until stiff peaks form.
In a small bowl, combine buttermilk, oil and vanilla. Whisk the remaining sugar and cinnamon. make a well in the center of the dry ingredients; add the wet ingredients and stir with a rubber spatula just until combined. Fold in apples, then the beaten egg whites. Spoon the batter into prepared pans, smoothing the tops. Sprinkle with reserved streusel. Bake the loaves 35-40 minutes or until lightly browned and a skewer inserted in the center comes out clean. Cool in the pans on a wire rack for 10 minutes. Remove from the pans and finish cooling on the rack.