Comparing submerged culture and solid state fermentation for the production of gluthatione

Glutathione conventionally is produced by submerged culture fermentation with the yeast S. cerevisiae using L-cysteine, L-glutamate and glycine as precursors. To obtain high glutathione concentrations in the yeast - as well as high reaction rates - optimum temperature and high precursor concentrations have to be maintained during fermentation. In submerged culture, due to dilution, large quantities of precursor are needed to obtain high precursor concentrations. In solid state fermentation increased precursor concentration is reached merely by the reduction of the water-holdup in the fermenter. Thus experiments were performed to compare submerged culture fermentation performed in a stirred tank reactor to solid state fermentation in a gas/solid fluidized bed reactor. A stirred tank reactor of 1.5 l volume was used to evaluate the influence of temperature, substrate composition, and precursor concentration on reaction rate and maximum glutathione accumulation in the yeast cells. A laboratory scale fluid bed fermenter of 0.15 m diameter and a technical scale fermenter of 1.0 m diameter with 42 kg of yeast were used to evaluate optimum feed strategy to optimize i) glutathione yield with respect to precursor feed and ii) the glutathione accumulation in the yeast cells. While in submerged culture maximum glutathione yield with respect to cysteine at maximum glutathione concentration ranged from 4 to 8 mole%, in solid state fermentation yields up to 40 mole% for glutathione produced during fermentation and up to 70 mole% for the total glutathione content were obtained.