Production of lactate and acetate by Lactobacillus coryniformis subsp. torquens DSM 20004T in comparison with Lactobacillus amylovorus DSM 20531T

Lactobacillus coryniformis subsp. torquens DSM20004T is a d-lactate producer, with a portion of the d-lactate higher than 99.9% of total lactic acid produced. Acetate was identified as the second end-product that appeared at the end of the exponential growth phase in MRS medium when glucose concentration dropped to 38.41 mM (6.92 g/L). The acetate production was prolonged to the stationary phase, while the concentration of d-lactate remained constant. Other end-products were not identified by HPLC method. The known metabolic pathways of glucose fermentation in lactic acid bacteria do not produce the particular combination of these two end-products, but besides lactate and acetate also formate, ethanol and CO2 are produced. For comparison, the production of lactate and acetate by a d-/l-lactate producer Lactobacillus amylovorus DSM 20531T was also investigated. This strain produced equimolar quantities of d- and l-lactate in the MRS medium. Acetate was produced only when initial concentration of glucose was 55.51 mM (10 g/L) and production started in the exponential phase when concentration of glucose dropped to 35.52 mM (6.40 g/L). Similar behavior was observed with the initial concentration of maltose of 29.21 mM (10 g/L). An unstructured mathematical model was established for the bioprocess simulation.