No abstract

The present

Introduction: 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.

This study was aimed to grow the local isolates yeast Candida tropicalis on locally prepared sawdust powder hydrolysate as a basal medium and carbon source with respect to single cell protein (SCP) production. The saw dust powder was treated with 10% H2SO4 for one hour at 100 0C. After cooling the supernatant containing the isolated sugar separated from debris by filtration and used as a carbon source and basal medium for yeast growth and SCP production. A high amount of SCP was achieved after five days of incubation, the percentage of the produced SCP 39.05% of the biomass dry weight, which is equivalent to 3.07g/l. SCP formation biosynthesis was affected by the level of nitrogen present in the medium; a high amount of protein being achieved in fermentation medium containing 0.3% urea in which the percentage of the yielded SCP was increased to 42.54%, (3.71g/l) of the biomass dry weight. The effect of varying nitrogen sources on SCP accumulation was also assayed. Medium containing ammonium phosphate greatly stimulated protein production in which the produced SCP was increased to reach 5.90 g/l. The produced amount equivalent to (48.22%) of the biomass dry weight. Conversely, a medium containing sodium nitrate had a suppressive effect on SCP production. This evidence clearly suggests that the metabolic versatility of Candida tropicalis may be employed in the conversion of low-grade material into high SCP product.