L-Glucono-1,5-lactone, also known as glucono delta-lactone (GDL), is a naturally occurring food additive and a cyclic ester of gluconic acid. It is a white, crystalline powder that is soluble in water. In aqueous solution, it hydrolyzes slowly to gluconic acid, which imparts a mild, non-astringent sourness. Its primary application is in the food industry as a versatile acidulant, leavening agent, and sequestrant. It is widely used in baked goods, dairy products (e.g., tofu, cheese), meat processing, and beverages to control acidity, texture, and shelf life. In the pharmaceutical industry, GDL serves as an excipient, particularly as a gentle, delayed-action acid source in effervescent tablets and as a disintegrant. Due to its slow hydrolysis, it provides a controlled pH decrease, making it valuable in systems requiring a delayed acid release. It is generally recognized as safe (GRAS) by regulatory bodies like the FDA for use in food.