Citric acid is a natural occurring fruit acid, produced commercially by microbial fermentation of a carbohydrate substrate. Citric acid is a weak organic acid found in citrus fruits. It is a good 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 and therefore occurs in virtually all living things. It also serves as an environmentally friendly cleaning agent and acts as an antioxidant.
Citric acid is the most widely used organic acidulant and pH-control agent in foods, beverages, pharmaceuticals and technical applications. Citric acid has a vital function in human and animal metabolism. Humans synthesise and break down an astonishing amount of citric acid - over 1.5 kg - every day. The citric acid cycle is one of the body's most important metabolic pathways. The main food constituents - carbohydrates, fat and some protein - are broken down into carbon dioxide and water, releasing energy for the body's various functions. Pure citric acid is a white crystalline powder.
The acidity of citric acid results from the three carboxy groups COOH which can lose a proton in solution. If this happens, the resulting ion is the citrate ion. Salts of citric acid containing this ion are called citrates. An important one is calcium citrate or "sour salt", which is commonly used in the preservation and flavoring of food.
First isolated from lemon juice by a Swedish chemist, Carl Wilhelm Scheele, in 1784, citric acid is manufactured by fermentation of cane sugar or molasses in the presence of a fungus, Aspergillus niger. It is used in confections and soft drinks (as a flavoring agent), in metal-cleaning compositions, and in improving the stability of foods and other organic substances (by suppressing the deleterious action of dissolved metal salts).
Citric acid is used to give lemonade, jams, sweets and confectioneries their characteristic acidulous flavour. It also plays an important role in the stabilization of oils and nutritional fats, and in vegetable, fruit, fish and meat preserves. It is used in the formulation of all effervescent tablets currently in pharmaceutical use, and in certain detergents.
As an edible acidifier, citric acid is widely used for its advantages of high solubility, least toxicity, strong chelating power and pleasant taste. It is applied as condiment, preservative (as in beverage and sweets), antioxidant when acting with ascorbic acid (as in fruit freezing) and pH adjustor (as in preparation of sweets and fruit jelly). Citrate sodium, citrate potassium and citrate calcium are proved safe and dependable as chelating agents and food dyes. Citric acid plays an important role in the pharmaceutical industry. It produces frothing effect when acid carbonate is to be made.