Improvement of L‐lactic acid production with a two‐step OUR control strategy

BACKGROUND Oxygen metabolism plays an important role in cell growth, metabolism and survival of microorganism. This report describes the effects of different oxygen metabolism levels on L‐lactic acid production by Lactobacillus paracasei, and then a new oxygen uptake rate (OUR) strategy is proposed based on integrated process physiological and metabolic analyses. RESULTS Physiological parameter, OUR, was introduced to quantitatively characterize oxygen metabolism in a microaerobic bioprocess for the first time, and 0.14 mmol L−1 h−1 was adopted as control to simulate industrial lactic acid production. During the growth phase, moderate to high OUR (0.43 mmol L−1 h−1) could promote cell growth, glucose consumption and L‐lactic acid production with little decrease in yield. However, when cells entered the stationary phase, significant glycolysis inhibition and pyruvate metabolism shift from lactic acid to acetoin occurred with 0.43 and 0.85 mmol L−1 h−1, both of which led to further L‐lactic acid production limitation. Through a new two‐step OUR control strategy with 0.43 mmol L−1 h−1 during the growth phase and 0.14 mmol L−1 h−1 during the stationary phase, productivity was enhanced 12.7% and the same yield was achieved as in the control. CONCLUSIONS OUR was identified to be a feasible process control parameter for microaerobic lactic acid production, and the OUR control strategy efficiently improved L‐lactic acid production.