O. M., Abonama, Hoda Mahrous, El baz A. F., and Hamza H. A. 2014. “Citric Acid Optimization by Candida Tropicalis under Submerged Fermentation Conditions Using a Plackett-Burman Design”. Journal of Life Sciences Research 1 (3):70-75. http://asianonlinejournals.com/index.php/Lifsc/article/view/607.