Glucono delta-lactone (GDL) is a naturally-occurring food additive used as a sequestrant, an acidifier, or a curing, pickling, or leavening agent. It is a lactone (cyclic ester) of D-gluconic acid. Pure GDL is a white odorless crystalline powder.

GDL is commonly found in honey, fruit juices, and wine. Being acidic, it adds a tangy taste to foods, though it has roughly a third of the sourness of citric acid. It is metabolized to glucose; One gram of GDL yields the roughly the same amount of metabolic energy as one gram of sugar.

Upon addition to water, GDL is partially hydrolysed to gluconic acid, with the balance between the lactone form and the acid form established as a chemical equilibrium. The rate of hydrolysis of GDL is increased by heat and high pH.