State the name of the optional ingredient of no.1397 recipe.
no.1397 recipe refers to recipe_id = 1397; optional ingredient refers to optional = 'TRUE'
SELECT T1.name FROM Ingredient AS T1 INNER JOIN Quantity AS T2 ON T1.ingredient_id = T2.ingredient_id WHERE T2.recipe_id = 1397 AND T2.optional = 'TRUE'