Almost all of the world’s output of citric acid, an intermediate in tricarboxylic acid cycle, is produced microbiologically. Citric acid cycle is a food preservative and flavoring agent of fruit juices, candy, ice cream, marmalade and other products. It is also used in pharmaceuticals as an iron chelator (binder), as a preservative for store blood, and in ointments and cosmetics. The chemical industry uses about 25 percent of the citric acid produced as a feedstock for making a variety of products.
Citric acid is commercially produced from sugar beet and cane molasses by Aspergillus niger, which is capable of converting 42 percent of the raw sucrose to citric acid. Because of complex regulatory mechanisms, citric acid accumulates as an intermediate and is excreted. The citric acid in the culture filtrate is then precipitated.