Selection of optimal conditions for the lactic acid biosynthesis

Lactic acid is used in various industries: chemical, food, cosmetic, pharmaceutical, agriculture and polymer production. 40% of the domestic market demand for lactic acid is met through imports, while the main methods for producing lactic acid are microbiological or synthetic. The most rational is microbiological synthesis, however, when it is implemented, valuable sugar-containing substrates (crystalline sucrose, molasses, sugar syrup) are used, which significantly affects the cost of the final product. There was an obvious need to search for new technologies for the production of lactic acid. Prospective and cost-effective is the processing of whey into lactic acid using bacterial fermentation of the lactose contained in the whey. The aim of the study is to screen cultures of microorganisms capable of fermenting lactose contained in milk whey and to select the composition of the medium that provides the maximum yield of lactic acid. Strains of lactic acid bacteria were used in the experiment: Leuconostocmesenteroides subsp. mesenteroides 122 (B1699), Lactobacillus brevis B78 (B5728), Lactobacillus plantarum K9 (B5466), Lactobacillus casei C1 (B5726), Lactobacillus acidophilus (B9012), Lactobacillus paracasei BT 24/88 (B6253), Lactobacillus paracasei 139 (B2430), obtained from the Russian National Collection of Industrial Microorganisms (Scientific Center "Kurchatov Institute" -Research Institute for Genetics and Selection of Industrial Microorganisms). The authors determined the optimal composition of the medium for the biosynthesis of lactic acid by selecting the concentrations of yeast autolysate and salt solution that provide the maximum yield of lactic acid. The authors also selected the optimal duration of lactic acid biosynthesis. The study of the acid-forming ability of strains of lactic acid bacteria showed that of the strains studied, Lactobacillus casei C1 (B5726) showed the greatest ability to ferment lactose by synthesizing lactic acid, which correlates with the data on assimilation of lactose by the culture. The optimal cultivation time (132 h) and the concentration of yeast lysate (5%) in a nutrient medium based on curd whey were selected. With optimal parameters, the maximum concentration of lactic acid in the culture liquid of Lactobacillus casei C1 (B5726) was 54.77 g / L, which is comparable with the currently used producers in the industrial production of lactic acid.