Effect of some physiological factors on citric acidproduction bythreeisolates ofAspergillus niger acid - hydrolyzed sawdust as a carbon source

Citric acid (2-hydroxy-propane-1, 2, 3-tricarboxylic acid) was first isolated from lemon juice in 1784. It is a primary metabolic product which is formed in the tricarboxylic acid (Krebs) cycle. It is estimated that the market value of citric acid will exceed two billion dollars in 2019. About 70% of total citric acid produced globally is utilized in food industry, while about 12% is utilized in pharmaceuticals and cosmetic industries and the remainder in other industrial purposes. The industrial production of citric acid is undertaken by fermentation process in the presence of filamentous fungi for large scale of production. Aspergillus niger is the most efficient fungus due to its ability to produce more citric acid per unit time and ferment different inexpensive raw materials. Materials and Methods: Three isolates of the fungus Aspergillus niger (An1, An2, An3) were used throughout this study using different carbon source concentration in the form of sawdust acid hydrolysis supplemented with different concentration of (NH4)2H2SO4 as a nitrogen source. The effect of hydrogen ion concentration and addition of methanol to the fermentation medium was also investigated. Results and Discussion: The results indicated that the optimization of carbon and nitrogen concentration had stimulatingeffect on citric acid production by the three used isolates. Moreover, addition of methanol at concentration of 1% at pH of 3.5 highly increased citric acid production. Conclusion: we concluded that the agriculture waste was a favorable substrate for the production of citric acid especially it is cost effective and easily obtainable.