COMPUTER-SIMULATION FOR L-LACTATE BATCH PROCESS EMPLOYING LACTOCOCCUS-LACTIS IO-1

L-lactate production employing Lactococcus lactis IO-1 demonstrated a typical end product inhibition. By numerical analysis results of the batch culture of this microorganism, 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 determined by process results. A mathematical model for batch culture growth of this microorganism in which the newly defined term alpha, a ratio of sterile cell formed to total cell population measured by optical absorbance was used, was constructed. By using this model, computer simulation was carried out and the batch culture growth gave satisfactory approximation to the observed results on the viable cell basis. However, the model gave a deviation from the observed results at the end phase of the growth. Further experiments showed that LDH activity in the solution, the key enzyme, decreased with a constant decreasing rate which is smaller than alpha. Simulation program using enzyme decreasing rate gave perfect results that agreed with the observed results for the whole batch.