KINETICS AND MODELING OF LACTIC-ACID PRODUCTION BY LACTOBACILLUS-PLANTARUM

An unstructured model was developed to describe bacterial growth, subs trate utilization, and lactic acid production by Lactobacillus plantar um in cucumber juice. Significant lactic acid production occurred duri ng growth, as well as stationary phases. The percentage of acid produc ed after growth ceased was a function of the medium composition. Up to 51% of the tactic acid was produced after growth ceased when NaCI was not present in the medium, whereas not more than 18% of the total lac tic acid was produced after the growth ceased in presence of NaCI, pro bably because of an increase in the cell death rate. An equation relat ing the specific death rate and NaCI concentration was developed. With the kinetic model proposed by R. Luedeking and E. L. Piret (J. Bioche m. Microbiol. Technol. Eng. 1:393-412, 1958) for lactic acid productio n rate, the growth-associated and non-growth-associated coefficients w ere determined as 51.9 (+/-4.2) mmol/g of cells and 7.2 (+/-0.9) mmol/ g of cells h(-1) respectively. The model was demonstrated for batch gr owth of L. plantarum in cucumber juice. Mathematical simulations were used to predict the influence of variations in death rate, proton conc entration when growth ceased, and buffer capacity of the juice on the overall fermentation process.