Continuous production of L-lactic acid from whey permeate by immobilized Lactobacillus casei subsp. casei

The production of L-lactic acid from whey permeate, a waste product of the dairy industry, by fermentation with the lactic acid bacterium Lactobacillus casei subsp. casei was investigated. A fermentation medium consisting of permeate and supplements, which enables exponential growth of the organisms, was developed. A fast method for determination of free and immobilized biomass in solid-rich media, based on measurement of cellular ATP, was evolved. Continuous fermentation in a stirred tank reactor (STR) and in a fluidized bed reactor (FBR) with immobilized biomass were compared. In the STR a volumetric productivity of 5.5 g/l per hour at 100% substrate conversion (dilution rate (D)=0.22 h high -1) was determined. In the FBR porous sintered glass beads were used for immobilization and a maximum biomass concentration of 105 g/kg support was measured. A productivity of 10 g/l per hour was obtained at D=0.4 h high -1 (substrate conversion 93%) and of 13.5 g/l per hour at D=1.0 h high -1 (s ubstrate conversion 50%).