Enhancing xanthine oxidase fermentation with pH-shift strategy based on kinetic analysis by Arthrobacter M3

The effect of initial culture pH and inducer concentration on xanthine oxidase (XOD) fermentation in shake flasks was first carried out. The results showed that the optimum initial culture pH and inducer concentration were 8.6 and 3.6 g/l, respectively. Batch fermentation of XOD by Arthrobacter M3 in a 7.5-l fermentor was then tested under various pH conditions ranging from 7.6 to 8.6. Based on the analysis of the obtained kinetic parameters, a pH-shift strategy in batch fermentation was implemented to enhance the XOD fermentation. In this strategy, the initial culture pH was set at 8.6 without control and was maintained at 7.6 after the biomass reached 2.0 g/l DCW. XOD production (P) and final average yield coefficient for production on biomass (FAY_p/x) in this strategy reached 7,415.3 U/l and 1,229.7 U/g, respectively, which were significantly higher than the results from the other four protocols. In pH-shift batch fermentation, the Luedeking–Piret equation for product accumulation and the Luedeking–Piret-like equation for substrate consumption fit well with the experimental values. The correlation coefficients (R ²) of these two fitting curves were 0.977 and 0.992, respectively.