Abstract
The effects of the substrate conditions on the volumetric productivity of Lactobacillus helveticus at different cell densities up to 60 g l−1 in a continuous stirred-tank reactor with microfiltration to retain the biomass were investigated. At low dilution rates, D, the steady-state volumetric productivity, rp, gradually increased to a maximum at D = 1.2–1.5 h−1, because of reduced product inhibition. At higher D values, rp unexpectedly decreased, although the substrate conditions further improved. The maxima of rp at different cell densities coincided with a critical specific substrate utilization rate beyond which the cell metabolism seems to be controlled through a catabolic modulator factor, and rp decreases.
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