Abstract: In order to improve glutathione production by Candida utilis SZU 07-01, the effects of addition of L-methionine and L-cysteine on glutathione biosynthesis during batch and fed-batch fermentation, respectively, were investigated. The results indicated that addition of L-methionine improved the glutathione biosynthesis ability of yeast during cell growth phase while addition of L-cysteine significantly enhanced the production of glutathione after cell growth. Based on this finding, a two-stage strategy for amino acid addition was proposed for high glutathione production, that is, 60 mmol/L of L-methionine was added into the medium at the beginning of fermentation (0 h), and 30 mmol/L of L-cysteine was then added when the biomass achieved the maximum level (27 h) during fed-batch culture. The two-stage strategy ultimately resulted in further improvements in glutathione production and intracellular glutathione content, which were 1 247.1 mg/L and 24.1 mg/g at 48 h, respectively. The successful application of the two-stage amino acid addition strategy for improved glutathione production also provides a feasible approach for the efficient production of other similar compounds.

Key words: Candida utilis, glutathione, L-methionine, L-cysteine, fed-batch fermentation