Kinetics and Modeling of Lactic Acid Production by Lactobacillus plantarum

An unstructured model was developed to describe bacterial growth, substrate utilization, and lactic acid production by Lactobacillus plantarum in cucumber juice. Significant lactic acid production occurred during growth, as well as stationary phases. The percentage of acid produced after growth ceased was a function of the medium composition. Up to 51% of the lactic acid was produced after growth ceased when NaCl was not present in the medium, whereas not more than 18% of the total lactic acid was produced after the growth ceased in presence of NaCl, probably because of an increase in the cell death rate. An equation relating the specific death rate and NaCl concentration was developed. With the kinetic model proposed by R. Luedeking and E. L. Piret (J. Biochem. Microbiol. Technol. Eng. 1:393-412, 1958) for lactic acid production rate, the growth-associated and non-growth-associated coefficients were determined as 51.9 (+/-4.2) mmol/g of cells and 7.2 (+/-0.9) mmol/g of cells h respectively. The model was demonstrated for batch growth of L. plantarum in cucumber juice. Mathematical simulations were used to predict the influence of variations in death rate, proton concentration when growth ceased, and buffer capacity of the juice on the overall fermentation process.