Study On Production Of Glutathione With Spent Brewer's Yeast And Separation

The fermentation and separation processes for the production of glutathione with spent yeast were studied.Firstly, the process of glutathione production with spent yeast was investigated to decide the fermentation period in shaking-flasks, and then the effects of medium compositions on the production of glutathione by spent yeast were discussed in shaking-flask culture. The investigation included the screening of nitrogen sources and carbon sources and the optimizing of their concentrations, the effects of salt ions, phosphates, MgSC>4, the three constituent amino acids of glutathione. The optimal medium consists of glucose 10g/l, MgS04 5g/l, K2HP04-3H20 lg/1, and KH2P04 lg/1.Based on the above studies, batch fermentation of glutathione was carried out in an aerated stirred-tank. The optimal fermentation parameters were determined. Because large amount of the spent yeast was added to the fermenter, the initial cell concentration in the broth was quite high. As a result, the air flux and the stirring speed must be maintained high in the process. The glutathione production was inhibited by high concentration of glucose, so the initial glucose conceritration should be limited. In order to enhance the glutathione production, fed-batch fermentation was appreciated.As the second part of the work, the separation of glutathione from spent yeast was also investigated. The oxidation of the glutathione(GSH) at deferent pH was discussed. Then the screening of ion-exchange resins, the dynamic exchange, as well as the adsorption abilities of ion-exchange resins for GSH were investigated. The two extraction agents including boiling water and ethanol were compared, and both of them have advantages and disadvantages.With the resins selected, the separation of glutathione by ion-exchange resin column was studied. At optimized conditions, the yield of glutathione was 65% by using macro-porous cation exchange resin (S-9), and the yield of glutathione was 33.7% by using macro-porous anion exchange resin (A-D3-4). The best macro-porous anion exchange resin selected, A-D3-4, showed low yield. So it was replaced by gel anion exchange resin (717). The yield of glutathione reached 49.6%. If the experiment conditions were optimized, the yield would be improved further.