450 http:/ / crmb.aizeonpublishers.net/ content/ 2014/ 4/ crmb450-456.pdf Current Research in Microbiology and Biotechnology Vol. 2, No. 4 (2014): 450-456 Research Article Open Access ISSN: 2320-2246 Optimum conditions for α- amylase production by Aspergillus niger mutant isolate using solid state fermentation Dalal S. Bedan, Ghazi M . Aziz and Ali J. R. Al - Sa’ady* Biotechnology Dept. College of Science, University of Baghdad, Iraq * Corresponding author: Ali J. R. Al - Sa’ady; email: ali.jabbar15@yahoo.com ABSTRACT Twenty one local isolates of Aspergillus niger were screened for their ability to produce α-amylase using solid- state fermentation (SSF), A. niger N11 local isolate exhibited maximum efficiency for amylase production, this isolate had been chosen for mutation by CO 60 Gamma ray. Several food wastes were used, such as wheat bran, potato peel, banana peel and corn cob. The highest yield of amylase produced from A. niger N11 mutant isolate was obtained with wheat bran when used as a substrate. Soluble starch and Ammonium nitrate (1%w/ w) used as the best additional carbon and nitrogen supplements respectively. The optimum pH, temperature and incubation period for α-amylase production by mutant isolate were found to be 5.5, 30 ° C and 6 days, respectively. Keywords: α- Amylase, Aspergillus niger , Gamma ray, Solid-state fermentation INTRODUCTION Amylases are a class of enzymes that are capable of digesting glycosidic linkages in starch components and glycogen molecules, these enzymes refer to glycoside hydrolase enzymes group which have enzyme commission number (EC:3.2.1). They are widely distributed in plant, microbial and animal kingdoms, which show varying in action patterns depending on the source. Amylases have significant applications in food, fermentation, textile, paper and pharmaceutical industries. Currently, they comprise about 30% of the world enzyme production [1]. Amylases are widely distributed in microorganisms (bacteria and fungi). Molds are capable of producing high amounts of amylase; Aspergillus niger is used for commercial production of α -amylase. Studies on fungal amylases especially in developing countries have concentrated mainly on Aspergillus niger, probably because of their ubiquitous nature and non-fastidious nutritional requirements of these organisms. It is possible to enlist the use of amylases under extreme condition of pH and temperature using thermo- acidophilic and alkaline amylases. [2]. For the microbial α-amylases production, two types of fermentation methods are mainly used : submerged and solid state fermentation .solid state fermentation system is reported to be the most appropriate process for developing countries ,because of the simplicity of the technique, superior volumetric productivity , low energy requirements , less water output, better product recovery, lack of foam build up. The low availability of water reduces the possibilities of contamination by bacteria and yeast, higher levels of aeration, low cost and availability of media employed in SSF [3]. The principle of solid state fermentation system derived from the nature or it is mimesis of the nature by which microorganism especially fungi preferred to grow in media nearly void of free water such as agricultural wastes, organic soil particles, cereals and fruit .The selection of a suitable microorganism is an important aspect of SSF for production of enzymes. The microorganism should be able to grow at low water activity (aw=0.6-0.7). Fungi and yeast were termed as suitable microorganisms for SSF (Solid state fermentation) according to the theoretical concept of water activity, whereas bacteria have been considered less suitable. However, experiences have shown that Received: 25 July 2014 Accepted: 12 August 2014 Online: 16 August 2014