Influence of initial glucose concentration on seed culture of sodium gluconate production by Aspergillus niger

Background: In general, high-quality seed is the prerequisite of an efficient bioprocess. However, in terms of sodium gluconate production by Aspergillus niger, reports have seldom focused on seed culture with rational optimization by process analysis technology, especially for carbon source effects. In this study, based on the online physiological parameter of oxygen uptake rate (OUR), and intracellular metabolite profiling, as well as cell morphology analysis, the effects of different initial glucose concentrations on seed culture by A. niger were investigated. Results: The optimum initial glucose concentration was 300 g/L, corresponding to 1900 mOsm/kg, with OUR level about 70% higher than other conditions. Besides, the cells from optimized seed culture accumulated more osmoprotectants of alanine and glutamate. Interestingly, high glucose concentration could induce glucose oxidase (GOD) activity possibly by affecting the synthesis of histidine, one key component of active site of GOD. Prominently, the fermentation yield using the optimized seed culture was up to 1.198 g/g, 99% of the theoretical value, which was the best in literature. Conclusion: The initial glucose concentration appropriately 300 g/L in seed cultivation was determined to be the most optimal. Further, this study would be helpful for guiding sodium gluconate production on industrial scale.