Citric acid is a weak organic acid. It is a natural preservative/conservative which occurs naturally in citrus fruits and is also used to add an acidic or sour taste to foods and drinks. In biochemistry, the conjugate base of citric acid, citrate, is important as an intermediate in the citric acid cycle, which occurs in themetabolism of all aerobic organisms. It consists of 3 carboxyl (R-COOH) groups.