Abdulatif, Muhamed Omar, et al. “Optimal Conditions For Production Acidic D-Xylanase By Aspergillus Niger in Submerged Fermentation”. Journal of Biotechnology Research Center (JOBRC), vol. 5, no. 3, Dec. 2011, pp. 14-21, doi:10.24126/jobrc.2011.5.3.174.