Cornstarch (Best Option)
1 tablespoon cornstarch per 1 tablespoon arrowroot powderCornstarch is a starch derived from corn and is widely used as a thickening agent. It gelatinizes at a similar temperature to arrowroot and creates a clear, glossy sauce which is ideal for tomato sauce where clarity and texture are important.
To use cornstarch effectively, mix it with an equal amount of cold water before adding to the hot sauce to avoid lumps. Cook the sauce just until thickened, as prolonged heating can cause cornstarch-thickened sauces to thin out.
Compared to arrowroot, cornstarch may produce a slightly less delicate texture but maintains a similar appearance and thickening strength, making it the best practical substitute in tomato sauce.