Screening Of Elite Aspergillus Niger Irradiated By Co～(60) Radiation For β-glucosidase Production And Its Fermentation Characteristics

β-glucosidase, which belongs to hydrolyase, is widely used in biodegradation of cellulose, improvement of food flavor and production of gardenia blue pigment. Aspergillus niger has been used to production ofβ-glucosidase because the strain needs simple nutrition and the production is an extracellular enzyme. But the output and activity ofβ-glucosidase from A. niger are so low that they can not meet the needs of marketplace. So screening of superior A. niger strain is of an practical significance.In this paper, a superior strain of A. niger was was selected and bred by Co⁶⁰ radiation. The medimum composition and fermentation technology forβ-glucosidase by A. niger on wheat bran are optimized by single and orthogonal tests. And the kinetic models describing cell growth andβ-glucosidase production were also established. The results would provide a basic work for the production ofβ-glucosidase by A. niger from wheat bran plenitudinous sources forβ-glucosidase applications in industrial scale.The results showed that the mortality was increased with the dosage of Co⁶⁰ radiation. The superior strain of A. niger was obtained when the dosage of Co⁶⁰ radiation was 400 Gy.The single-factor test showed that the optimum components of mediums forβ-glucosidase production by parent and mutant strain of A. niger were as following: wheat bran 20 g/L, (NH₄)₂SO₄ 1g/L, KH₂PO₄ 2g/L, MgSO₄·7H₂O 0.2g/L, FeSO₄·7H₂O 0.01g/L.The single-factor test showed that the optimum conditions for the fermentation of parent and mutant strain of A. niger in shake flasks were volume on fermentation of 70 ml/250 ml, rotary rate of 200±5 r/min and 2504±5 r/rain, and temperature of 304±0.5℃with inoculum size of 15% and 10%, respectively.The conditions of theβ-glucosidase production from by parent and mutant strain of A. niger were also researched through orthogonal test. As the result, the optimum conditions for the fermentation of parent and mutant strain in shake flasks were rotary rate of 200±5 r/rain and 250±5 r/rain, and temperature of 304±0.5℃with inoculum size of 15% and 10%, respectively.β-glucosidase production reached 1103.73 U/ml and 6968.54 U/ml by parent and mutuant strain whileβ-glucosidase activity was increased 5 fold by mutant strain after 3 days of fermentation under the optimum conditions. Based on Monod equation and Luedeking-Piret equation, the kinetic models describing cell growth andβ-glucosidase production were established. Time course analysis of fermentation showed that the cell growth and the synthesis ofβ-glucosidase in mutant strain advanced 16 h than in original strain, and also showed the part-coupled relationship between the synthesise ofβ-glucosidase and cell growth.