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
A. Gonzalez-vara et al., 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, BIOTECH BIO, 67(2), 2000, pp. 147-156
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.