الفهرس 
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Abstract
The present study was conducted for the possible utilization of water hyacinth plant (Eichhornia crassipes), one of the worst invasive aquatic plants in Egyptian environment, as a substrate for production of microbial xylanase under different fermentation techniques. Among 10 tested microorganisms, Bacillus amyloliquifaciens NRRL B-14393 showed the highest activity of extracellular cellulase-free xylanase under solid-state fermentation of water hyacinth plant (stem & leaves). Distilled water was the most suitable extraction solution. Different fermentation parameters were studied for optimization of production process. Xylanase yield was enhanced 2.33 fold as compared to unoptimized condition ( 232.37 U/ g wet substrate ; 4674.4 U/g dry substrate) by growing the bacteria on 10 g of fresh plant supplemented with 0.5 % sucrose at 35 C with initial pH 6.0, 7.0 % inoculum size and an initial moisture level of 95% for 24 hours. No nitrogen source or additives were required for enhancing the enzyme yield. Purification of B. amyloliquifaciens xylanase was done using DEAE-Sepharose and Sephadex G-100 columns which affected specific activity (1009.14 U/mg) and 18.67 purification fold. The pure xylanase has molecular weight 34.679 and 29 KDa by gel filtration and SDS-polyacrylamide gel electrophoresis ,respectively. The pure xylanase showed a maximal activity at pH 9.5(5mM Tris-HCl) and 50C. Using birch wood xylan as a substrate, xylanase had a Km value of 2.94mg ml-1and Vmax of 10.92 µmole min-1 ml-1.The enzyme was nearly completely inhibited by MnSO4 and HgCl2at 1&10mM concentration. B. amyloliquifaciens xylanase was consisting of 17 amino acids and rich in aspartic acid and tyrosine. End product analysis of the purified xylanase by HPLC, revealed that the enzyme was of the type of non-arabinose liberating endoxylanase. The resulted xylooligosaccharides (XOS) mixture exhibited potent antioxidant activity. Enzymatic degradation of some pretreated agricultural residuesusing the crude B. amyloliquifaciensxylanase showed promising results.XOS were obtained from the respective pretreated agricultural residues by the crude xylanase action in a range 54.4%-85.5%. XOS mixtures of orange and mango peels exhibited relatively higher antioxidant activities and total phenolic acid contents compared to the other XOS mixtures.