الفهرس 
Introduction
Citric acid-producing microorganismsOnly 14 pages are availabe for public view
 |  | from | 151 |  |  |
| | | from | 151 | | |
Abstract
Citric acid is one of the most important organic acids in the foods and pharmaceutical industries, citric acid had extracted from natural resources specially citrus fruits, then citric acid was begin to produced with using Aspergillus niger. This study aim to use Aspergillus niger to produce citric acid by screening some strains which can produce citric acid and screening some media which used for citric acid production, then to reach the maximum citric acid production some factors were studied. The first section including screening nine stains of Aspergillus niger, six of it were local CA1, CA2, CA3, CA4, CA5, CA6 and three of it were exported from USA. It were namely NRRL 2270, NRRL 3 NRRL 67. Six cultural media were used as basal media for citric acid production cultivation was made in 250 ml. Erlenmeyer flasks, each containing 100 ml of sterile medium. The flasks were incubated at 30(R@(BC on a rotary shaker at 150 r.p.m.. It could observe that the best strain of citric acid producer was A. niger CA2 on medium No.2, which had cane molasses. The second section including studying the factors affecting on citric acid production as follows The best time of fermentation, the optimum, total sugars, the treatment with K4Fe(CN)6 and ammonium oxalate, nitrogen sources and the best concentration of it, phosphoric acid was used as phosphorus sources with a concentration of 0.3 ml/L, 0.2 g/L magnesium sulfate was used, the optimum inoculum volume, were investigated and there were no positive effect on the production citric acid with the adition of several trace metal ions or ethanol. The third section was using the fermenter. The fourth section was studied the effect of the immobilized spores with calsium algenate, and useing this immobiliezd spores as an inoculum to produce citric acid. The possibility of citric acid production was 51.1 g/L in fermentor by the selected stain No, 2, meduim which containing (g/L): sugar cane molasses 272, ammonium phosphate 2, phosophoric acid 0.3 ml, magnesium sulfate 0.2, pH 5.5, at 30?C, after eight days of fermentation.