What is the name of the starch that leaks out when heated to thicken a sauce?

The starch that leaks out when heated to thicken a sauce is primarily amylopectin, a component of starch molecules. When starch granules are heated in liquid, they gelatinize and release amylopectin, which thickens the sauce. This process is commonly utilized in cooking with ingredients such as flour, cornstarch, or other starchy thickeners.