Enhanced Lactic Acid Production by Adaptive Evolution of Lactobacillus paracasei on Agro-industrial Substrate

The aim of this study was to perform the adaptation of Lactobacillus paracasei NRRL B-4564 to substrate through adaptive evolution in order to ensure intensive substrate utilization and enhanced L (+)-lactic acid (LA) production on molasses-enriched potato stillage. To evaluate the strain response to environmental conditions exposed during the adaptation process and to select the best adapted cells, the antioxidant activity and LA-producing capability were assessed in batch fermentation. The most promising adapted strain was further used in a pulsed fed-batch mode. Among three selected adapted strains, L. paracasei A-22 showed considerably improved antioxidant capacity, demonstrating more than onefold higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging rates compared to parent strain. This strain also exhibited superior LA production in batch fermentation and reached 89.4 g L^-1 of LA, with a yield of 0.89 g g^-1, a productivity of 1.49 g L^-1 h^-1, and an optical purity greater than 99%. Furthermore, in fed-batch mode L. paracasei A-22 resulted in 59% higher LA concentration (169.9 g L^-1) compared to parent strain (107.1 g L^-1). The strain adaptation to molasses environment, performed in this study, is a rather simple and promising method for enhancement of LA production on the complex agro-industrial substrate.