Productivity and properties of a Weizmannia coagulans strain capable of synthesizing L-lactic acid

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Abstract
Studies on the producers of L-lactic acid are highly relevant at the moment due to the broad scope of its applications. This study was aimed at selecting culture parameters for a milk-derived thermophilic strain of Weizmannia coagulans that is capable of producing L-lactic acid. It was found that the strain productivity depends on the culture temperature, stirring rate, medium pH, used neutralizing agent, and glucose concentration. The culture in flasks and a fermenter revealed that in 56 hours, the strain is capable of producing up to 80.4 g/L of lactic acid at a corresponding average productivity of 1.44 g/(L×h) with a conversion of about 99%. The most optimal parameters to achieve the highest indicators were a temperature of 50 °С, medium pH of 6.5, and a stirring rate of 150 rpm. This strain was shown to be uninhibited by high glucose concentrations; conversely, it exhibited higher productivity at glucose concentrations of 100–120 g/L in the medium. Among the neutralizing agents used for pH adjustment, the Ca(OH)2 agent was selected, which has the least effect on the size of producer cells during fermentation and whose by-products are the least toxic. The obtained results indicate that further studies on the metabolic properties and genetic modification of this strain are required in order to increase productivity, reduce the inhibitory effect of the target product on the metabolism of the producer, and obtain elevated lactic acid titers in a short fermentation time.

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