Citric acid production by Yarrowia lipolytica

Recently, with an increasing annual demand of more than two million tons, citric acid (CA) has become the main additive and functional component in the food, pharmaceutical, and chemical industries. This rising demand has induced research to search for alternative and cheap ways to fulfil CA requirements in industry. Lately, Yarrowia lipolytica has been considered as a promising microorganism in the production of CA since it has many advantages over moulds: mainly high productivity, easier cultivation (convenient for continuous process), and the capability to use a wide range of agricultural or industrial by-products and wastes as cheap carbon sources. CA production by this yeast depends on certain factors such as medium composition (type and concentrations of carbon, nitrogen, and trace elements) and the type of strain used (wild, mutant, or genetically engineered), as well as cultivation conditions (pH, temperature, dissolved oxygen, etc.). This review principally details recent studies concerning CA production by Y. lipolytica with an emphasis on techniques to increase productivity and yield to meet the expanding demand for this organic acid. Suitable substrates and production factors for high and cost-efficient CA production are discussed. Downstream processes and production systems are also reviewed.