Amino sugars comprising six carbon atoms, with glucosamine and galactosamine as the best-known examples. They are structural units in chitin, glycosaminoglycans, and bacterial cell walls, and they surface in food science through shellfish-derived ingredients such as glucosamine, through fermentation microbiology, and in the analytical chemistry of carbohydrates. Because they bridge carbohydrate and nitrogen chemistry, they matter in studies of Maillard-type reactions and of functional ingredients derived from crustacean shells. Their identification in a food matrix usually signals either a specific added ingredient or the natural biochemistry of the raw material.