Definition of 'optimum'. optimum (ÉptÉªmÉm ) or optimal. The optimum or optimal level or state of something is the best level or state that it could achieve. Aim to do some physical activity three times a week for optimum health. ...regions in which optimal conditions for farming can be created.
Use Tapioca Flour. Also know as tapioca starch, it's a great substitute. You'll want to use 2 tablespoons for every 1 tablespoon of cornstarch. Use Rice Flour. Rice flour thickens up like regular flour so use the same proportion: 3 tablespoons for every 1 tablespoon of cornstarch.
Arrowroot does give a glossy appearance in recipes. The downside of arrowroot is that it is not likely to be on hand in a pinch, and it still requires a longer cooking time in order to receive the same thickening result. Other acceptable substitutions for cornstarch include tapioca and rice or potato starch. Tapioca is a good substitute if the recipe requires chilling after cooking. Rice or potato starch are good substitutes if the recipe is to be frozen after cooking.