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Articles by Mahmoud M. Berekaa
Total Records ( 3 ) for Mahmoud M. Berekaa
  Mahmoud M. Berekaa , Yasser R. Abdel-Fattah and Hany M. Hussein
  An experimental design technique was carried out to investigate the bioaccumulation of chromium VI by the rubber degrading nocardioform actinomycete Gordonia polyisoprenivorans VH2. Response Surface Methodology (RSM) was adopted to acquire the best level of four variables namely, pH, FeSO4, NaNO2 and Cr (VI) which have been optimized to bring about maximum chromium biosorption percentage. In this respect, the 3-level Box-Behnken design was employed. A polynomial model has been created to correlate the relationship between the four variables and chromium biosorption. The optimal combination of those variables for chromium biosorption evaluated from the non-linear optimization algorithm of EXCEL-Solver was as follows (mg L-1): FeSO4, 18; NaNO2, .75; Cr (VI), 41.25 at pH 6.7. Based on the predicted model, an experimental verification of the optimal conditions revealed chromium biosorption percentage of 90%, which is more than 3 folds the basal medium.
  Gahda A. Youssef and Mahmoud M. Berekaa
  In this study, bagasse was used as substrate for endoglucanase (carboxymethyl-cellulase; CMCase) production using locally isolated Aspergillus terreus and the culture parameters were optimized for enhancing cellulase yield. The fungus showed 0.9 U mL-1 endoglucanase (CMCase) activity, during growth on basal salts medium at 35oC, initial pH value of 5.5 and in presence of 5% bagasse as a sole c-source. Preliminary experiments to address the most suitable nitrogen source as well as the optimal substrate (bagasse) treatment revealed that the optimal enzyme activity were 2.1 and 2.43 U mL-1 in presence of 3 g yeast extract and 1 N HCl or 1 NaOH, respectively. Statistically based experimental design was applied to optimize the production of endogluconase by A. terreus. To evaluate the effect of different culture conditions on the production of CMCase enzyme, Plackett-Burman factorial design was carried out. Twelve variables were examined for their significance on enzyme production. Treated bagasse (T2), non treated bagasse (NT), K2HPO4, NaNO3, trace elements, KCl, temperature and pH were the most significant factors encourage CMCase enzyme production, whereas treated bagasse (T3), yeast extract and MgSO4, were the most significant factors decreasing CMCase enzyme production. The pre-optimized medium showed approximately 4 folds increase in cellulase enzyme production.
  Yasser R. Abdel-Fattah , Nadia A. Soliman and Mahmoud M. Berekaa
  Optimization of poly-γ-glutamic acid (PGA) produced by the glutamate-independent Bacillus licheniformis SAB-26 has been carried out using response surface methodology. Predicted maximum PGA yield (57.9 g L-1) was calculated using non-linear optimization algorithm powered by Microsoft Excel, where the optimized medium composition was (g L-1): casein hydrolysate, 12.2; ammonium sulfate, 20; K2HPO4, 27 and KH2PO4, 27 after 72 h. A verification experiment was carried out to compare predicted and experimental results, where experimental yield reached (59.9 g L-1) in a good sign of model validity. Pulsed feeding experiment of citrate at different time intervals revealed increasing the polymer production to 88 g L-1.
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