Oyeniran, O.O., et al. “A Modeling Study by Response Surface Methodology on the Culture Parameters Optimization of Citric Acid Bioproduction from Sweet Potato Peel”. Ife Journal of Technology, vol. 22, no. 1, May 2013, pp. 21-25, http://ijt.oauife.edu.ng/index.php/ijt/article/view/117.