Optimal production of glutathione by controlling the specific growth rate of yeast in fed‐batch culture

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Abstract
The optimal of the specific growth rate was obtained with simple mathematical model in a yeast fed‐batch cultures. The model was based on the mass balance around the fed‐batch system and the relationship between the specific growth rate, μ, and the specific production rate of glutathione, ρG. The optimal profile of μ was calculated as a bang–bang type, That is μ, should start from the maximum value, μmax and should be kept at μmax; then μ should be switched to μc, which gives a maximum value of ρG. It was proven from the maximum principle that switching was needed only once, with the switching time from μmax to μc depending on the final required glutathione content. Finally, this ideal profile of μ for the maximum production of glutathione was realized by manipulating the substrates feed rate in the fed‐batch culture. Using the extended Kalman filter and a programmed‐controller/feedback‐compensator (PF) system, μ could be controlled at the optimal profile obtained. As a result, the maximum production of glutathione was accomplished fairly successfully. However, further improvement in the controller performance for μ is desired. The control strategy employed here can be applied to other batch reaction processes.