High cell density culture of baker's yeast FX‐2 based on pH‐stat coupling with respiratory quotient

The high cell density culture of baker's yeast FX‐2 was investigated in a 50 L(A) automatic bioreactor. Herein, it was found firstly that the Crabtree effect clearly existed in batch fermentation with higher glucose content, then the critical initial glucose content range (≤2.00 g L−1) was reasonably ascertained to effectively avoid Crabtree effect. In the next fed‐batch fermentations with different strategies, the second strategy (maintain ethanol concentration lower than 0.10% and pH around 4.80) was confirmed to be more beneficial to yeast growth than the first strategy (keep reducing sugar not more than 2.00 g L−1 and control steady Carbon/Nitrogen ratio 3.05:1.00). After that, one optimal control strategy (maintain pH around 4.80 and keep respiratory quotient in the range of 0.90–1.00) was constructed to further enhance cell yield. Under an optimal control strategy, four schemes with the aim of achieving pH‐stat were compared, and yeast extract instead of other alkaline materials was selected as a better regulator. As a result, 148.37 g L−1 dry cell weight, 38.25 × 108 mL−1 living cells, and 8.24 g L−1 h−1 productivity were harvested, which respectively elevated 23.74%, 135.38%, and 24.47% compared to that obtained under the traditional scheme (regulate pH with ammonia); meanwhile, the maximum oxygen uptake rate and carbon dioxide excretion rate were both more than 250.00 mmol L−1 min−1.