Unstructured model for seed cultures without pH control ofLactobacillus helveticus growing on supplemented whey permeate

Abstract

In cultures of Lactobacillus helveticus with pH controlled at 5.9, growth and lactic acid production were under the control of nutritional limitations (carbon and nitrogen). In the absence of pH control, as was the case for seed cultures, an inhibitory effect on growth of both pH and the undissociated lactic acid concentration were evident before nutritional limitations. The variations of the specific growth rate with the undissociated lactic acid concentration followed exponential decay. Then, the inhibitory effect of pH was also taken into account through the Henderson–Hasselbach equation. The specific growth rate history has been previously found to follow sigmoidal variation. Integration of these relationships gave the theoretical biomass and lactic acid production kinetics. The model fitted experimental kinetic data well and allowed fine analysis of the various growth phases, since the growth-associated, the deceleration and the stationary states can be characterized by means of the model parameters. © 2002 Society of Chemical Industry