Enhancement of Glutathione Production by Combining Cysteine Addition with Dissolved Oxygen Control and Low pH Stress in High Cell Density Cultivation of Candida utilis

The effects of cysteine addition coupled with dissolved oxygen(DO) control and pH stress on glutathione(GSH) production in high cell density(HCD) cultivation of Candida utilis were investigated.By applying HCD cultivation,cell concentration reached 102 g/L and GSH yield was 981 mg/L after 45 h fermentation.At 45 h,single-shot addition of cysteine was utilized to increase GSH production,the results indicated that the 50 mmol/L cysteine addition achieved a maximal GSH yield of 1534 mg/L after 60 h cultivation.In addition,the method of two-step DO control after cysteine addition,by which DO was controlled at 5% in the first 3 h and at 20% in the following 12 h,was developed.As a result,cysteine addition was decreased from 50 to 30 mmol/L,while GSH yield reached 1734 mg/L at 60 h.Moreover,by adopting the strategy of combining two-shot cysteine addition(15 mmol/L for each time) with two-step DO control and low pH stress,a maximal GSH yield of 1936 mg/L was achieved at 60 h.