Citric acid is an organic acid, belongs to Carboxylic Acids , first isolated in 1784 by Carl Wilhem Scheele.

How can we extract citric acid from lemon juice? Citric acid is isolated by precipitating it with to calcium oxide to yield calcium citrate salt, from which citric acid is regenerated by treatment with sulphuric acid.
Citric acid (that occurs in the metabolism of almost all living things) exists in a huge variety of fruits and vegetables and can be found in woods, mushrooms and even in tobacco. Lemon juice contains a 5-7% of citric acid.

Many production processes are now provided by the industrial technology: citric acid, actually, can be manufactured  in bioreactors, in a low pH (acid) and low iron environment, by sugar fermentation of microorganisms such as the transgenic fungus Aspergillus niger. During this process, citric acid cycle is disturbed and  the fungus expel citric acid.

Citric acid is a white crystalline solid substance, water soluble, chemically composed by 3 carboxyl acids, 3 hydroxyl acids  and 1,5 pentaionics. In the dry state, it occurs as rhombic crystals and taken, in very small doses, assists bone tissue regeneration.
An overdose is dangerous: toxicity test have measured a death rate of 50%, in rats receiving 3gr/kg.

Use

Citric acid is widely used in food industries as acidifier and preservative for food and beverages; it is denoted by E number E330.

In pharmaceuticals, citric acid provides the acid source in effervescent tablets in addition to being used to adjust pH. It’s also employ to produce cianographic paper, in printing tissue and as metal cleaner.
It’s often used in detersive production to abridge hard water (limescale), because it captures calcium salts.

In medicine, it‘s considered an excellent blood coagulator along with sodium (sodium citrate) and it’s often supportive in some renal calculus diseases.
It sounds strange, but citric acid is a real panacea to decrease body acidity.

Among all its properties…

Citric acid aids hyperglycaemic patients, reducing the sugar amount in blood.