Comprehensive evaluation of the biosynthetic potential of Lactobacillus delbrueckii strains in lactic acid synthesis

Aim. To perform a comprehensive evaluation of the biosynthetic potential of Lactobacillus delbrueckii strains in lactic acid synthesis for potential industrial use. Methods. The study examined four strains of Lactobacillus delbrueckii capable of synthesizing lactic acid (LA). The concentration of lactic acid in the fermentation broth at the end of fermentation was determined using high-performance liquid chromatography. The concentration of free reducing sugars in the nutrient medium was analyzed by a modified Bertrand method at the beginning of the process and by either the Bertrand or Somogyi-Nelson method at the end. Results. The biosynthesis of lactic acid by four L. delbrueckii strains (PB-07, UY-2/13, BMP-92, Q-50) was studied under varying concentrations of carbon sources and nitrogen sources, as well as under optimal (40 C, without stirring) and suboptimal (30 C and 50 C, with stirring) fermentation conditions. One strain, L. delbrueckii UY-2/13, demonstrated characteristics suitable for commercial production, achieving a biosynthesis yield of approximately 70 g/dm3 using an inexpensive nitrogen source in batch cultivation with high initial glucose concentrations. The study revealed that physical parameters have a significant influence on the process. A fermentation temperature of 50 C strongly inhibited lactic acid biosynthesis, while the inhibitory effect at 30 C was less pronounced. Additionally, pH adjustment and temperature control during fermentation require precise regulation to avoid adverse effects. Conclusions. The L. delbrueckii UY-2/13 strain is a promising candidate for lactic acid production. Its cultivation on cost-effective raw materials, such as low-cost corn extract, could enhance the economic viability of the process.