Grate the sweet potatoes, onion, apple and carrot. Ring out the shavings in a cheese cloth or paper towel (this is to ensure the pancakes won't be soggy). Then in a large bowl, place shredded sweet potatoes, grated onion, grated apple, grated carrot, 2 egg whites and 1/4 cup flour. Then add 1/2 teaspoon salt and 1/2 teaspoon pepper. Mix well.