| Summary: | 碩士 === 大葉大學 === 生物產業科技學系碩士在職專班 === 95 === There were 42 strains of Bacillus subtilis var. natto for γ-glutamic acid (γ-PGA) production isolated from commercial natto foods or dried powder of natto strains to investigate the degrading fibrin activity of nattokinase (NK) in this study. Only19 strains selected from 42 B. natto were able to degrade fibrin. The DYU-28 isolated strain with the high NK activity (about 12.56 FU/mL) was further studied for improving the activity. It was found that the optimum composition of the culture medium for DYU-28 was investigated to be 6.0% glucose, 4.5% wheat bran, 1.5% yeast extract, 0.4% K2HPO4 and 0.2% CaCO3. With this culture medium (initial pH = 6.5), the NK activity of DYU-28 was up to 220 FU/mL after 48 h of flask cultivation at 37℃ and 150 rpm for 48 hr. Furthermore, 5-L fermentor was used to study the optimum scale-up conditions for DYU-28. The highest NK activity was up to 505 FU/mL for DYU-28 with 5% inoculum size under the optimum conditions of temperature at 37℃, pH controlled at 6.5, aeration rate at 3 vvm, and agitation at 300 rpm, after 58 h of fermentation.
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