| There are many investigations concerning feed compound enzymes. Most of earlier studies, however, focus on multi-strains producing feed compound enzymes. Few studies deal with single strain. Aiming at improving the present unsatisfactory produc ing of enzymes with single strain, we screened a high yield compound enzymes producing strain from original strain and optimized the fermentation process as well. Moreover, the leaching, purification and characteristic of acid protease from Aspergillus. niger variation strain SL2-111 were also discussed in this dissertation.1. A highly productive compound enzymes strain variation strain SL2-111 was screened from its original strain Asp. niger FJ-008 by treating with UV as well as complex mutagen of UV and NTG. There were of some differences between Asp. niger variation strain SL2-111 and Asp. niger FJ-008. Colonies appeared after SL2-111 had been cultured on standard medium for 30 h and Asp. niger FJ-008 for 20 h. The spores of variation strain SL2-111 appeared early and around the clone there were few radiate veins. The color of pigment on the back of clone was light and few wrinkles were visible there.The activities of enzyme produced from SL2-lllwere 4525 U/g for acid protease, 7015 U/g for pectinase and 4497 U/g for cellulase, which were enhanced 97.9%, 70.1% and 13.4% compared to the original strain's, respectively. Its properties for high yield producing compound enzymes remained stable after five times of subculture. In addition, correlation analysis by SPSS 10.0 showed that there were positive correlation between the activity of acid protease and pectinase, acid protease and cellulase. According to the result, the activity of acid protease could be regarded as the response in selecting the strains.2. The solid fermentation condition of SL2-111 was studied by using single-factor research and orthogonal test based on the response value of acid protease. The result showed that the medium with high content of carbon and low content of nitrogen was fit for the growing of SL2-111. The optimal medium contained 8.25 g fresh bran, 4.5 g rice bran, 1.5 g cake bean,0.3 g (NH^SCu, 0.06 g K2HPO4, 0.075 g CaCl2, 8.6 ml water. The initial pH was set at 5.5, and culture temperature was controlled at 28"C in first 30 h and 23 癈 in later 30 h. The fermentation process could be divided into two phases, growing phrase and spore and enzyme producing phrase. In the latter phase there appeared quantity of mycelia and almost no enzymes produced. The enzyme activities of acid protease, pectinase and cellulase were 6428 U/g, 8245 U/g and 4911 U/g respectively when the strain was grown on the optimal medium under the above culture conditions in 250 ml Erlenmeyer flask.3. The present study investigated the leaching of acid protease from fermented solid medium with different solutions: 0.1M citrate buffer (pH 3.5), distilled water, 0.1M HCI and 2% NaCl. From this experiment, 0.1M lactic buffer (pH 3.5) was chosen for leaching because of its efficient recovery. Compared with that of 2% NaCl, the recovery ratio was enhanced by 50%. Following this, to determine the optimum leaching factors, the proteases were leached with various solution pH, leaching time, leaching solution and leaching ratio. The result indicated that 0.1M Na2HPC>4-Citric acid buffer of pH 5.0 gave optimal recovery with the temperature setting to 40*C, the ratio of leaching solution to enzyme being 10:1 and leaching time lasting for 60 min.4. The acid protease was purified from the crude enzyme product of Asp. niger variation strain SL2-11 with ammonium sulfate, ion exchange chromatography and gel filtration in Sephadex G-75 in sequence. After purification, the component S-l was gained and the enzyme preparation demonstrated a single band in SDS-PAGE, suggesting that the intended aim of purification had been reached.5. The purified acid protease produced by SL2-11 was active between pH 4.0-5.5 with optimal activity at pH 3. It had good thermostability and exhibited maximum activity at 60 "C, which m...
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