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Journal of Biological Sciences
Year: 2001  |  Volume: 1  |  Issue: 5  |  Page No.: 401 - 411

Production Physiology of Cellulases and β-glucosidase Enzymes of Aspergillus niger Grown under Solid State Fermentation Conditions

M. Fadel    

Abstract: A new isolate of A. niger F-119 was utilizaed to produce endoglucanase (EC 3. 21. 4) exoglucanase (EC 3. 2. 1. 91) and 13- glucosidase (EC 3. 2. 1. 21) adopting the solid state fermentation condition using radicle waste as main substrate. Cultural conditions including moisture level, incubation period, initial pH, incubation temperature and inoculum size were evaluated. The fungus expressed high enzymes production at moisture level 70% (w /w), initial pH 4.5, inoculum size 10% (v/w) at 32°C after 72h which yielded 31.5, 46.0 and 215.2 I U/g original sub st rate. Supplementation of the culture medium with ammonium sulphate (at a level of 20 mg N/g substrate) enhanced enzyme activities. Similarly, wheat bran at 20% (w/w) was the most suitable carbon source for o b taining high enzyme yields. Sucrose at level 1% (w/w) was found to be more effective for enzymes biosynhesis raising the enzymes levels to 59.2, 74.4 and 445 I U/g substrate of FPase, CMCase and β-glucosidase respectively. The distribution of the solid medium at 1.5 cm proved to be suitable for enzymes production wherein the process can be successfully repeated for four different cycles. Partial purification with ammonium sulphate showed that the protein fraction obtained at 20%-40% ammonium sulphate saturation was most suitable for enzymes recovery. The enzymes were found to be active and stable at temperatures 55, 65 and 60°C, p H 4.5, 5.5 and 4.5. The effect of treatment with different concentrations of sodium hydroxide on delignification of wheat straw substrate and thus enhancing the enzymatic hydrolysis of wheat straw was markedly accelerated after treatment with 4.5% NaOH solution.

The partially purified 20-40% ammonium sulphate precipitate enzymes fraction and mouldy substrate were compared with crude enzyme extract to hydrolyze the alkali-treated wheat straw. The highest hydrolysis 82.8% was obtained using mouldy substrate. The enzymatic hydarolyzate containing 68% glucose of total sugars. The enzymatic hydrolyzate of the alkali-treated wheat straw was fermented for 48h by Saccharomyces cerevisiae and hybrid of S. cerevisiae has the ability to convert pentoses to enthanol 29.1 and 35.9 gram ethanol/100 g alkali-treated wheat straw were yielded by the two strains respectively.

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