Enhanced production of L-(+)-lactic acid in chemostat by Lactobacillus casei DSM 20011 using ion-exchange resins and cross-flow filtration in a fullyautomated pilot plant controlled via NIR

Due to the lack of suitable in-process sensors, on-line monitoring of ferme ntation processes is restricted almost exclusively to the measurement of ph ysical parameters only indirectly related to key process variables, i.e., s ubstrate, product, and biomass concentration. This obstacle can be overcome by near infrared (NIR) spectroscopy, which allows not only real-time proce ss monitoring, but also automated process control, provided that NIR-genera ted information is fed to a suitable computerized bioreactor control system . Once the relevant calibrations have been obtained, substrate, biomass and product concentration can be evaluated online:and used by the bioreactor c ontrol system to manage the fermentation. In this work, an NIR-based contro l system allowed the full automation of a small-scale pilot plant for lacti c acid production and provided an excellent tool for:process optimization. The growth-inhibiting effect of lactic acid present in the culture broth is enhanced when the growth-limiting substrate, glucose, is also present at r elatively high concentrations. Both combined factors-can result in a severe reduction of the performance: of: the lactate production process. A dedica ted software enabling on-line NIR data acquisition and reduction, and autom ated process management through feed addition, culture removal and/or produ ct recovery by microfiltration was developed in order to allow the implemen tation of continuous fermentation processes with recycling of culture mediu m and cell recycling. Both operation; modes were tested at different diluti on rates and the respective cultivation parameters observed were compared w ith those obtained in a conventional continuous::fermentation. Steady state s were obtained in both modes with high performance on lactate production. The highest lactate volumetric productivity, 138 g L-1 h(-1), was obtained in continuous fermentation with cell recycling. (C) 2000 John Wiley & Sons, Inc.