Control of cell growth rate by sugar feeding based on CO2 production rate

Sugar feeding based on the CO₂ production rate was investigated for the control of the cell growth rate during cephalosporin C fermentation in which sugar concentration was the growth limiting factor. The rates of cell growth and sugar consumption were apparently influenced by the sugar feed rate, as the sugar concentration in the broth was kept at approximately 1 g/l during the cultivation. The ratio of the CO₂ production rate to the sugar consumption rate was maintained almost constant after 40 h cultivation. Stepwise alteration in sugar feed rate after the culture time of 50 h caused a change in the CO₂ production rate within 15 min. These results indicated that the CO₂ production rate could be used as an effective parameter of sugar consumption and cell growth rates. Consequently, a control strategy was developed that involved the control of sugar feed rate so that a CO₂ production rate profile corresponded to a preset standard profile. For the half the usual amount of inoculum, the sugar feeding control system enabled the cell concentration to increase faster to that in the usual inoculum. The cell concentration deviation during exponential growth phase among several batches, decreased to half using this sugar feeding control system compared to the culture without such control. These results indicated that the sugar feeding control system developed in this report was found to be efficient for control of cell growth.