Citric acid is a weak organic acid, and it is a natural preservative and is also used to add an acidic, or sour, taste to foods and soft drinks. In biochemistry, it is important as an intermediate in the citric acid cycle and therefore occurs in the metabolism of virtually all living things. It can also be used as an environmentally benign cleaning agent.
As a food additive, citric acid is used as a flavoring and preservative in food and beverages, especially soft drinks. Citrate salts of various metals are used to deliver those minerals in a biologically available form in many dietary supplements. The buffering properties of citrates are used to control pH in household cleaners and pharmaceuticals.
In water softening, citric acid’s ability to chelate metals makes it useful in soaps and laundry detergents. By chelating the metals in hard water, it lets these cleaners produce foam and work better without need for water softening. In a similar manner, citric acid is used to regenerate the ion exchange materials used in water softeners by stripping off the accumulated metal ions as citrate complexes.The saturation point for citric acid and water is 59%.
Citric acid is the active ingredient in some bathroom and kitchen cleaning solutions. A solution with a 6% concentration of citric acid will remove hard water stains from glass without scrubbing. In industry it is used to dissolve rust from steel. Citric acid can be added to ice cream to keep fat globules separate, and can be added to recipes in place of fresh lemon juice as well. Citric acid is used along with sodium bicarbonate in a wide range of effervescent formulae, both for ingestion and for personal care.
Citric acid is used in biotechnology and the pharmaceutical industry to passivate high-purity process piping (in lieu of using nitric acid). Citric acid is also used in shampoo, as a stop bath as part of the process for developing photographic film, in food coloring to balance the pH level of the normally basic dye, and as a delay to prompt natural cement.