Optimization of amino acids addition for efficient production of glutathione in Candida utilis

Strategy of precursor amino acids addition for glutathione (GSH) synthesis was optimized in this study. The addition of cysteine and glycine showed a significant effect on GSH accumulation. Cysteine increased intracellular GSH content greatly but inhibited cell growth at the same time. A two-step amino acids addition strategy was developed. First, 6 mmol/L glycine was added at 4 h, and a mixture of glutamic acid, glycine and cysteine was added at 12 h at stationary phase of cell growth. The optimum concentrations of three amino acids (glutamic acid, 6 mmol/L; glycine, 5.5 mmol/L; cysteine, 6.5 mmol/L) were obtained by response surface methodology.With the two-step addition strategy, biomass and GSH yield reached 11.65 g/L and 241.4 mg/L in flask experiments, increased by 10.5% and 69.5%, respectively, as compared with the control without amino acids addition.By applying this amino acid addition strategy further to batch fermentation in 7 L fermentor, GSH yield reaches 383.3 mg/L, which is 78.1% higher than the control.