In a mixing bowl, combine egg whites, milk, bread crumbs, and black pepper. Add chicken and mix well. Shape into 12 meatballs. In a large saucepan, heat oil over medium heat. Add meatballs and cook until no pink remains in chicken. Remove meatballs from pan. In same saucepan, combine sauerkraut and onions. Stir in rice and water. Add meatballs and pureed tomatoes. Bring to a boil. Reduce heat and simmer, covered for 30 minutes or until rice is done.