BACKGROUNDUtilization of wastes and industrial by-products for production of valuable bio-based chemicals has economic and environmental advantages. The aim of this study was to investigate utilization of two industrial by-products, distillery stillage and sugar beet molasses combined as a substrate for lactic acid and biomass production. A selection of the most appropriate lactic acid bacteria that could effectively utilize this waste substrate was performed. In addition, the effect of initial sugar concentration on lactic acid production and growth of lactic acid bacteria on the combined waste substrate was evaluated. RESULTSLactobacillus paracaseiNRRL B-4564 was selected as the most promising for lactic acid production on distillery stillage and sugar beet molasses. The highest lactic acid productivity of 1.42 g L-1 h(-1) and yield of 0.91 g g(-1) were achieved on stillage/molasses media at initial sugar concentration of 56.74 g L-1. The highest number of L. paracasei cells at 5.3 x 10(9) CFU mL(-1) was achieved at initial sugar concentration of 78.22 g L-1. CONCLUSIONCombined distillery stillage and sugar beet molasses could provide valuable nutrients for growth of fastidious lactic acid bacteria and enable efficient lactic acid production, while processing industrial waste in this way has great environmental relevance. (c) 2015 Society of Chemical Industry