| Summary: | 碩士 === 國立中興大學 === 食品科學系 === 91 === Hemicelluloses, which comprise mainly xylans, are abundant biomass resources in the nature. However, xylans remain to be a less utilized resource. Xylanase production from a fungal isolate, Aspergillus niger NCH-3 was used in this study. The objectives of this work were to determine the optimum pH and agitation rate for cultivation of cells using a 5 L bench-top bioreactor. In addition, some catalytic properties of Asp. niger NCH-3 xylanase using coba husk hemicellulose as substrate, and separation of the xylooligosaccharides by activated charcoal were also studied.
Asp. niger NCH-3 was cultivated in a medium containing 1% coba husk hemicellulose, 1% corn steep liquor, and 0.38% KNO3 at 35℃ for 5 days. The maximum xylanase activity with 28.56 U/ml was obtained at pH 6.0 with 170~200 rpm agitation rate, and aerated at 1.0 vvm.
Crude or ammonium sulfate precipitation-purified xylanase were chemically modified by different chemical reagents. The tryptophan, histidine and arginine residues in xylanase molecule was inactivated by some specific reagents. This indicated that tryptophan, histidine and arginine residues were involved in the active site or substrate binding site of the enzyme.
Degree of hydrolysis of coba husk hemicellulose by the xylanase from varied slightly with different pH values, the pH values ranged from 4.0 to 5.0 for optimum hydrolysis condition. Presence of 2.5 g/L of nonionic surfactant Tween 20 increased hydrolysis ability of xylanase.
Combination of activated charcoal-celite (2：1, w/w) was chosen for adsorption and separation of xylooligosaccharides from hydrolysates of coba husk hemicellulose, and the continuous mode was superior to batch mode in the elution of sugars adsorbed. Up to 90.36% of xylobiose could be recovered from the absorbed sugars by using 5% alcohol as an eluant.
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