Batch culture growth model for lactate fermentation

Abstract

l-Lactate fermentation using Streptococcus sp. IO-1 had a typical end product inhibition. By numerical analysis of fermentation results of the batch culture of this microorganism, it was found that the specific rates for cell growth, substrate consumption, and product formation were clearly expressed by the end product inhibition formulae. All constants for those formulae were calculated from the fermentation results. A mathematical growth model for batch culture of this microorganism was constructed. Computer simulation was done using this mathematical model. By the simulation work, the batch culture growth which expressed by the mathematical model with a ratio of sterile cells formed to total cell population measured by O.D. (α) gave satisfactory approximation to the observed results. Comparisons between computer simulation and fermentation results showed that cell growth at the beginning after lag phase was expressed by the exponential function without α to last for almost the same number of hours in any operation and sterile cell formation started with a constant α. Thus the microorganism growth should be classified into three phases; the lag phase, exponential growth phase without sterile cell formation, and exponential phase with sterile cell formation instead of the conventional classification; lag, exponential growth, linear growth, stationary, and death phases. In all of these phases except lag phase, cell growth is regulated by the end product concentration.