Preheat oven to 350. Peel, seed, and finely chop apples. Grease 12 muffin cups or line with paper liners; set aside. Combine dry ingredients in medium bowl. Combine and add eggs, apple juice concentrate, melted butter, and vanilla; mix just until dry ingredients are moistened. Stir in apple and walnuts. Spoon batter into prepared cups, filling each cup 3/4 full. Bake 25 minutes, until golden brown. Let stand in pan on wire rack 5 minutes. Remove from pan. Serve warm or at room temperature. Cooled muffins may be wrapped securely and frozen up to 3 months.