Citric acid is an organic acid found a variety of fruits and Acidity regulators vegetables, but it is most concentrated in lemons and limes. It is a natural preservative and is also used to add an acidic (sour) taste to foods and soft drinks. In biochemistry, it is important as an intermediate in the citric acid cycle or Krebs cycle (see the last paragraph) and therefore occurs in the metabolism of almost all living things. Excess citric acid is readily metabolized and eliminated from the body. Citric acid is an antioxidant. It is also used as an environmentally friendly cleaning agent.