Production of l-lactic acid by a thermophilic Bacillus mutant using sodium hydroxide as neutralizing agent
2010
Qin, Jiayang | Wang, Xiuwen | Zheng, Zhaojuan | Ma, Cuiqing | Tang, Hongzhi | Xu, Ping
A sodium lactate tolerant mutant strain named Bacillus sp. Na-2 was obtained and applied to sodium hydroxide-based l-lactic acid (LA) production process. The influences of aeration and pH were investigated to further improve the resistance of strain Na-2 against sodium lactate stress and to obtain the most efficient l-LA production process. Although mild aeration was favorable for cell growth and l-LA production, vigorous aeration resulted in a metabolic shift from homolactic to mixed-acid/acetoin fermentation. Therefore, a two-stage aeration control strategy was employed. Optimum pH was found to be 6.0. A total of 106.0g/l l-LA was produced in 30h by Bacillus sp. Na-2 using sodium hydroxide as neutralizing agent. Productivity, conversion rate and optical purity were 3.53g/l/h, 94% and 99.5%, respectively. The remarkable fermentation traits of Bacillus sp. Na-2 and the environment-friendly characteristics of NaOH-based process represent new insight for industrial scale production of l-LA.
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